Guidance for Industry 
 
Clinical Data Needed to Support the 
Licensure of Seasonal Inactivated 
Influenza Vaccines 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Additional copies of this guidance are available from the Office of Communication, Training and 
Manufacturers Assistance (HFM-40), 1401 Rockville Pike, Suite 200N, Rockville, MD 20852-
1448, or by calling 1-800-835-4709 or 301-827-1800, or from the Internet at 
http://www.fda.gov/cber/guidelines.htm. 
 
For questions on the content of this guidance, contact the Division of Vaccines and Related 
Product Applications at 301-827-3070. 
 
 
 
U.S. Department of Health and Human Services 
Food and Drug Administration 
Center for Biologics Evaluation and Research 
MAY 2007  Contains Nonbinding Recommendations 
 
 
Table of Contents 
 
 
I.  INTRODUCTION.............................................................................................................2 
II.  BACKGROUND...............................................................................................................3 
III.  CLINICAL DATA TO SUPPORT THE LICENSURE OF SEASONAL 
INACTIVATED INFLUENZA VACCINES..................................................................4 
A.  Traditional Approval of a BLA for a New Seasonal Inactivated Influenza 
Vaccine...................................................................................................................4 
1.  Effectiveness.....................................................................................................4 
2.  Additional Studies to Support the Effectiveness of the Vaccine in Populations 
Not Included in the Clinical Efficacy Study.....................................................5 
3.  Safety................................................................................................................6 
4.  Pediatrics...........................................................................................................7 
B.  Accelerated Approval of a BLA for a New Seasonal Inactivated Influenza 
Vaccine...................................................................................................................7 
1.  Effectiveness.....................................................................................................9 
2.  Safety..............................................................................................................10 
3.  Postmarketing Confirmatory Studies..............................................................11 
C.  Additional Considerations..................................................................................11 
1.  Types of Influenza Vaccines...........................................................................11 
2.  Clinical Lot Consistency.................................................................................11 
3.  Adjuvanted Seasonal Inactivated Influenza Vaccines....................................12 
4.  Pediatric Research Equity Act........................................................................13 
5.  Postmarketing Evaluations..............................................................................14 
IV.  REFERENCES................................................................................................................15 
i  Contains Nonbinding Recommendations 
 
Guidance for Industry 
 
Clinical Data Needed to Support the Licensure of Seasonal 
Inactivated Influenza Vaccines 
 
 
This guidance represents the Food and Drug Administrations (FDAs) current thinking on this 
topic.  It does not create or confer any rights for or on any person and does not operate to bind 
FDA or the public.  You can use an alternative approach if the approach satisfies the 
requirements of the applicable statutes and regulations.  If you want to discuss an alternative 
approach, contact the appropriate FDA staff.  If you cannot identify the appropriate FDA staff, 
call the appropriate number listed on the title page of this guidance. 
 
 
 
I.  INTRODUCTION 
 
This document is intended to provide to you, sponsors of seasonal inactivated influenza vaccines, 
guidance on clinical development approaches to support a Biologics License Application (BLA).  
The approaches in this guidance apply to both nonadjuvanted and adjuvanted hemagglutinin-
based seasonal vaccines, including split virus, subunit, and whole virus inactivated vaccines 
propagated in embryonated chicken eggs or cell-culture, and to recombinant hemagglutinin-
based protein vaccines, and DNA vaccines that express hemagglutinin.  This document does not 
address live attenuated influenza vaccines or influenza vaccines that do not rely on immunity to a 
hemagglutinin component.   
 
We, FDA, recognize that in the past there have been monovalent and bivalent inactivated 
influenza vaccines for seasonal influenza.  To provide flexibility for evolving public health 
needs, including the development of vaccines with either more than three or fewer than three 
antigens, this guidance uses the term seasonal inactivated influenza vaccine.   
 
This document does not address the nonclinical or early clinical development of investigational 
vaccines.  Successful evaluations of nonclinical and early clinical development are important 
steps before proceeding with additional clinical development (Ref 1).  This document also does 
not address the chemistry, manufacturing, control, or inspection of the manufacturing facility 
needed for licensure.  These aspects of the license application are addressed in the guidance 
document entitled, Guidance for Industry:  Content and Format of Chemistry, Manufacturing, 
and Controls Information and Establishment Description Information for a Vaccine or Related 
Product. 1  Applicants may contact the Center for Biologics Evaluation and Research (CBER) 
for additional information about these aspects of vaccine development.  
 
                                                 
1 See http://www.fda.gov/cber/vaccine/vacpubs.htm. 
2  Contains Nonbinding Recommendations 
 
FDAs guidance documents, including this guidance, do not establish legally enforceable 
responsibilities.  Instead, guidances describe the FDAs current thinking on a topic and should be 
viewed only as recommendations, unless specific regulatory or statutory requirements are cited.  
The use of the word should in FDAs guidances means that something is suggested or 
recommended, but not required. 
 
 
II.  BACKGROUND 
 
Influenza viruses are enveloped ribonucleic acid viruses belonging to the family of 
Orthomyxoviridae and are divided into three distinct types on the basis of antigenic differences 
of internal structural proteins (Ref. 2).  Two influenza types, Type A and B, are responsible for 
yearly epidemic outbreaks of respiratory illness in humans and are further classified based on the 
structure of two major external glycoproteins, hemagglutinin (HA) and neuraminidase (NA).  
Type B viruses, which are largely restricted to the human host, have a single HA and NA 
subtype.  In contrast, numerous HA and NA Type A influenza subtypes have been identified to 
date.  Type A strains infect a wide variety of avian and mammalian species. 
  
Type A and B influenza variant strains emerge as a result of frequent antigenic change, 
principally from mutations in the HA and NA glycoproteins.  These variant strains may arise 
through one of two mechanisms:  selective point mutations in the viral genome (Refs. 3 and 4) or 
from reassortment between two co-circulating strains (Refs. 5 and 6).   
 
Since 1977, influenza A virus subtypes H1N1 and H3N2, and influenza B viruses have been in 
global circulation in humans.  The current U.S. licensed inactivated trivalent vaccines are 
formulated to prevent influenza illness caused by these influenza viruses.  Because of the 
frequent emergence of new influenza variant strains, the antigenic composition of influenza 
vaccines needs to be evaluated yearly, and the trivalent iinnaaccttiivvaatteedd influenza vaccines are 
reformulated almost every year.  The immune response elicited by previous vaccination may not 
be protective against new variants.  
 
The Centers for Disease Control and Preventions (CDCs) Advisory Committee on 
Immunization Practices (ACIP) has expanded the recommendations for receipt of influenza 
vaccination to include an increasing scope of at risk populations, currently including pregnant 
women, persons 50 years of age and older, and children 6 to 59 months of age (Refs. 7, 8, and 9).  
Increased demand for influenza vaccines, including that resulting from the broader 
recommendations, the withdrawal from the U.S. market by several influenza vaccine 
manufacturers, and intermittent decreases in vaccine production due to manufacturing problems 
have led to shortages or delays in the availability of influenza vaccine over the past several 
seasons.  These shortages highlight both the complexity of the production process and the need 
to increase the availability of influenza vaccines from multiple manufacturers.  Currently, even 
with full production, manufacturing capacity would not produce enough seasonal influenza 
vaccine to vaccinate all those for whom the vaccine is now recommended.  Finally, the 
availability of adequate supplies of licensed seasonal inactivated influenza vaccines from 
multiple manufacturers will be of value in responding to the emergence of a new pandemic 
influenza strain.   
3  Contains Nonbinding Recommendations 
 
III.  CLINICAL DATA TO SUPPORT THE LICENSURE OF SEASONAL 
INACTIVATED INFLUENZA VACCINES 
 
Licensure of seasonal inactivated influenza vaccines may be sought through the submission of an 
application by means of either a traditional or accelerated pathway.  This Section provides 
recommendations for clinical data to support traditional and accelerated license approvals for 
new seasonal inactivated influenza vaccines.  CBER has prepared similar guidance for pandemic 
influenza vaccines, Guidance for Industry:  Clinical Data Needed to Support the Licensure of 
Pandemic Influenza Vaccines. 2
 
A.  Traditional Approval of a BLA for a New Seasonal Inactivated Influenza 
Vaccine 
 
Biological products are licensed under the authority of section 351 of the Public Health 
Service Act (PHS Act) (42 U.S.C. 262).  Under section 351, BLAs are approved only 
upon a showing that the product is safe, pure and potent, and that the manufacturing 
facility meets standards designed to assure that the biological product continues to be 
safe, pure, and potent.  In previously issued guidance entitled, Guidance for Industry:  
Providing Clinical Evidence of Effectiveness for Human Drug and Biological Products 
dated May 1998 (section II.A.), FDA stated, Potency has long been interpreted to 
include effectiveness (21 CFR 600.3(s)).  In 1972, FDA initiated a review of the safety 
and effectiveness of all previously licensed biologics.  The Agency stated then that proof 
of effectiveness would consist of controlled clinical investigations as defined in the 
provision for adequate and well-controlled studies for new drugs (21 CFR 314.126), 
unless waived as not applicable to the biological product or essential to the validity of the 
study when an alternative method is adequate to substantiate effectiveness (21 CFR 
601.25(d)(2)). 3  
 
1.  Effectiveness 
 
As discussed above, demonstration of effectiveness against influenza illness in an 
adequate and well-controlled clinical study would support licensure of a new 
seasonal inactivated influenza vaccine.  In this document, a clinical endpoint 
efficacy study refers to a clinical trial in which influenza illness is assessed as the 
primary endpoint.  The study design should take into account the following 
parameters: 
 
a.  The study population should be carefully considered.  A placebo-controlled 
clinical efficacy study conducted in a population that is not at increased risk 
for complications from influenza would allow for a precise estimation of 
clinical effectiveness against influenza illness (absolute efficacy).  The ACIP 
usually lists, at least annually, those persons who are considered to be at 
increased risk for influenza complications; we will rely on that list (Ref. 10).   
                                                 
2 See http://www.fda.gov/cber/vaccine/vacpubs.htm.  
3 See http://www.fda.gov/cber/guidelines.htm. 
4  Contains Nonbinding Recommendations 
 
Alternatively, a population at increased risk for influenza illness 
complications may be studied, but an adequate sample size should be used to 
demonstrate non-inferiority of the new vaccine to a U.S. licensed product with 
regard to clinical effectiveness. 
 
b.  The case definition for influenza illness should be prospectively defined.  
Inclusion of culture confirmation, viral typing and antigenic characterization 
in the case definition increases the specificity.  The increased specificity 
allows for a more precise estimate of vaccine effectiveness and would likely 
reduce the sample size needed to assess effectiveness.  Additionally, culture 
confirmation would facilitate interpretation of study results in the event that 
circulating influenza strains do not match antigen components contained 
within the vaccine.  An analysis of whether the immune response elicited by 
the vaccine correlates with protection against influenza illness will depend 
upon the use of a specific case definition (e.g., culture confirmation of 
influenza).  
 
c.  Study sample size calculations should be based on estimates of vaccine 
effectiveness and influenza attack rates.  The study should be powered to 
assess the lower bound of the two-sided 95% confidence interval (CI) of 
vaccine effectiveness, anticipated to be substantially above zero (e.g., in the 
range of 40 to 45%).  
 
d.  Immunogenicity evaluations in a substantial number of study participants are 
important elements of the study design.  Characterization of the immune 
response elicited post-vaccination in the clinical endpoint efficacy study may 
allow for extrapolating the effectiveness to other populations if they have an 
immune response to vaccination comparable to that observed in the clinical 
endpoint efficacy study.  Furthermore, immune response data collected in the 
course of a prospectively designed clinical endpoint efficacy study may lead 
to the establishment of an immune correlate of protection.  Such a correlate 
could greatly facilitate future influenza vaccine development.  
 
2.  Additional Studies to Support the Effectiveness of the Vaccine in Populations Not 
Included in the Clinical Efficacy Study 
 
Some populations who are at increased risk for complications from influenza 
vaccination (e.g., individuals 6 to 59 months of age and those 65 years of age and 
older) may not have been included in the clinical endpoint efficacy study because 
of the challenges in conducting a comparative efficacy study.  Effectiveness 
studies in these populations can be based on appropriate immunogenicity 
endpoints.   
 
a.  Immunogenicity bridging studies can be conducted to compare the immune 
response observed in the clinical endpoint efficacy study to that elicited in 
other populations.  Appropriate endpoints may be the hemagglutination 
5  Contains Nonbinding Recommendations 
 
inhibition (HI) antibody responses to each viral strain included in the vaccine.  
Studies should be adequately powered to assess the following co-primary 
endpoints for each of these viral strains:  1) geometric mean titer (GMT), and 
2) rates of seroconversion, defined as the percentage of subjects with either a 
pre-vaccination HI titer < 1:10 and a post-vaccination HI titer > 1:40 or a pre-
vaccination HI titer > 1:10 and a minimum four-fold rise in post-vaccination 
HI antibody titer.  (See recommendations for these endpoints outlined in 
Section III.B.1.a.).  Point estimates and the two-sided 95% CI of these 
evaluations should be provided in the BLA.  While this approach may expand 
the use of the new vaccine in additional populations, an important 
consideration is that immune responses in the very young and the elderly 
might be lower than those observed in healthy adults enrolled in a placebo-
controlled clinical endpoint efficacy study.  Additionally, changes to the 
annual formulation of the vaccine might complicate the design of such studies.  
Identification of an immune correlate of protection during the course of a 
clinical endpoint efficacy study may facilitate the design and interpretation of 
such bridging studies.  
 
b.  Alternatively, non-inferiority immunogenicity studies comparing a new 
vaccine to a U.S. licensed seasonal vaccine may support the use of the new 
vaccine in populations not included in the clinical endpoint efficacy study.  
This is true when the comparator vaccine is indicated for use in the population 
under study and when the comparator vaccine has clinical effectiveness data 
(i.e., not a U.S. licensed seasonal inactivated vaccine granted accelerated 
approval with its clinical benefit awaiting confirmation).  Studies should be 
adequately powered to assess the co-primary endpoints for HI antibodies to 
each viral strain contained in the vaccine:  1) GMT, and 2) seroconversion 
rates (as outlined in Section III.B.1.a.).   
 
3.  Safety 
 
The safety of the new vaccine should be well characterized in pre-licensure 
clinical trials.  Local and systemic reactogenicity events should be well defined in 
all age groups for whom approval of the vaccine is sought.  Appropriate grading 
scales to describe the severity of the adverse events should be included in the 
study protocol.4  Serious adverse events must be monitored and collected for all 
subjects throughout the duration of the studies (21 CFR 312.23, 312.32, 312.56, 
312.60 and 312.62).  The protocol should include a clinic visit or telephone 
contact at least six months post-vaccination to ascertain additional serious adverse 
events and new onset of chronic illnesses that may have occurred in the interim.   
                                                 
4 For further information, see the FDA Draft Guidance for Industry:  Toxicity Grading Scales for Healthy Adult 
and Adolescent Volunteers Enrolled in Preventive Vaccine Clinical Trials available at 
http://www.fda.gov/cber/vaccine/vacpubs.htm.  This draft guidance, when finalized, will represent FDAs current 
thinking on this topic. 
6  Contains Nonbinding Recommendations 
 
For vaccines using novel manufacturing processes and/or adjuvants, laboratory 
safety tests including hematologic and clinical chemistry evaluations, may be 
needed pre-and post-vaccination in the first clinical studies.  Depending on those 
findings and pre-clinical data, additional clinical laboratory tests in later studies 
may be needed. 
 
The total size of the safety database should depend, in part, on the range of the 
age indication being sought, signals raised during pre-clinical studies and early 
clinical studies, and the amount of clinical experience associated with the 
particular manufacturing process and the adjuvant, if one is included in the 
influenza vaccine.  It is anticipated that data will be collected in adults and in the 
pediatric population in a step-wise fashion.  We assume that approval for use in 
the adult population, including the geriatric population, would be sought with the 
initial application.  We recommend that you assess the safety of your 
investigational vaccine in several thousand subjects who receive the product in 
the controlled clinical trials described above.  You are encouraged to initiate an 
early dialogue with CBER to agree on the size of the safety database needed to 
support product licensure. 
 
4.  Pediatrics 
 
The timing of the clinical development and the size of the safety database to 
support use in the pediatric age groups warrants discussion with CBER.  Please 
refer to Section III.C.  Additional Considerations, paragraph 4, for a discussion 
of the Pediatric Research Equity Act (PREA). 
 
B.  Accelerated Approval of a BLA for a New Seasonal Inactivated Influenza 
Vaccine 
 
Accelerated approval may be granted for certain biological products that have been 
studied for their safety and effectiveness in treating serious or life-threatening illnesses 
and that provide meaningful therapeutic benefit over existing treatments.  (See 
Accelerated Approval of Biological Products for Serious or Life-Threatening Illnesses 
(21 CFR Part 601, Subpart E)). 
 
Such an approval will be based on adequate and well-controlled clinical trials 
establishing that the biological product has an effect on a surrogate endpoint that is 
reasonably likely, based on epidemiologic, therapeutic, pathophysiologic, or other 
evidence, to predict clinical benefit (21 CFR 601.41).  Approval under this section will be 
subject to the requirement that the sponsor study the biological product further, to verify 
and describe its clinical benefit, where there is uncertainty as to the relation of the 
surrogate endpoint to clinical benefit (21 CFR 601.41).  Postmarketing studies must also 
be adequate and well-controlled and should be conducted with due diligence (21 CFR 
601.41).  The protocols for these studies should be submitted with the original BLA.   
 
7  Contains Nonbinding Recommendations 
 
Marketing approval for biological products approved under these regulations may be 
withdrawn, for example, if the postmarketing clinical study fails to verify clinical benefit 
or the sponsor fails to perform the required postmarketing study with due diligence (21 
CFR 601.43(a)(1) and (2)). 
 
The option to pursue an accelerated approval pathway for seasonal inactivated influenza 
vaccines is also available to sponsors if a shortage of influenza vaccine exists for the U.S. 
market at the time the new vaccine is approved.  We interpret the accelerated approval 
regulation, 21 CFR 601.40, as allowing accelerated approval of an influenza vaccine 
during a shortage because influenza is a serious and sometimes life-threatening illness. 
Providing prophylaxis to those who would not otherwise be immunized during a shortage 
does certainly provide a meaningful benefit over the then-existing treatments, which are 
in short supply at that time.  We understand a shortage to exist when the supply of 
influenza vaccine is inadequate to immunize all persons for whom the CDC recommends 
annual vaccination.  The CDC estimates that there are 185 million individuals in the 
United States for whom influenza vaccination is recommended annually (Ref. 11).   
 
For influenza vaccines, the immune response elicited following receipt of the vaccine 
may serve as a surrogate endpoint that is likely to predict clinical benefit, that is, 
prevention of influenza illness and its complications.  Influenza virus hemagglutinins, 
present on the viral surface, are important for cell-receptor binding.  The immune 
response to the hemagglutinin as measured by the presence of serum HI antibodies is an 
important protective component following vaccination and/or infection.  However, 
considerable variability can be introduced into the laboratory assay used to measure HI 
antibodies as a result of a number of factors including differences in viral strains and red 
blood cell types, and the presence of non-specific inhibitors in the assay medium.  Thus, 
suitable controls and assay validation are important for interpreting HI antibody results.   
 
To date, prospectively designed studies to evaluate the effectiveness of influenza 
vaccines have not identified a specific HI antibody titer associated with protection against 
culture confirmed influenza illness.  Some studies of influenza infection, including 
human challenge studies following vaccination, have suggested that HI antibody titers 
ranging from 1:15 to 1:65 may be associated with protection from illness in 50% of 
subjects and protection from illness is increased with higher titers (Refs. 12 and 13).  
Seroconversion and GMT have been used as measures of vaccine activity (Refs. 14 and 
15). 
 
For the purposes of accelerated approval of seasonal inactivated influenza vaccines, the 
HI antibody response may be an acceptable surrogate marker of activity that is 
reasonably likely to predict clinical benefit.   
 
To be considered for accelerated approval, a BLA for a new seasonal inactivated 
influenza vaccine should include results from one or more well-controlled studies 
designed to meet immunogenicity endpoints and a commitment to conduct confirmatory 
postmarketing studies of clinical effectiveness in preventing influenza during the next 
influenza season.  Since each vaccine candidate is unique (e.g., particular product 
8  Contains Nonbinding Recommendations 
 
characteristics, manufacturing process, etc.), we recommend that you discuss with CBER 
early in development the adequacy of the manufacturing methods and product testing and 
the extent of the clinical data needed to license your candidate vaccine. 
 
1.  Effectiveness 
 
This Section describes possible approaches for establishing effectiveness based on 
immune responses under an accelerated approval.  We are open to considering 
other study designs, and other surrogate endpoints reasonably likely to predict 
benefit, along with other proposed performance targets for the surrogate endpoints 
described below or for other surrogate endpoints. 
 
a.  A non-inferiority immunogenicity trial of HI antibody responses to the new 
vaccine as compared to a U.S. licensed seasonal inactivated influenza vaccine 
(except for those granted accelerated approval whose clinical benefit awaits 
confirmation) may support an accelerated approval.  The study should be 
adequately powered to assess the co-primary endpoints for HI antibodies to 
each viral strain contained in the vaccine (e.g., a total of six co-primary 
endpoints for a trivalent vaccine):  1) GMT, and 2) seroconversion rates.  
Recommendations for the co-primary endpoints include the following:  
 
  The upper bound of the two-sided 95% CI on the ratio of the GMTs 
(GMT   /GMT ) should not exceed 1.5.  A proposal 
U.S. licensedvaccine new vaccine
for use of a different GMT ratio should be based upon the characteristics 
of the assay that will be used to assess antibody responses. 
 
  The upper bound of the two-sided 95% CI on the difference between the 
seroconversion rates (Seroconversion   - Seroconversion
U.S. licensed vaccine  new 
) should not exceed 10 percentage points.   
vaccine
 
b.  Alternatively, a placebo-controlled immunogenicity trial in which HI antibody 
responses to the new vaccine are assessed may be supportive of accelerated 
approval if the study is adequately powered to assess the co-primary endpoints 
for HI antibodies to each viral strain contained in the vaccine:  1) 
seroconversion rates, and 2) percentage of subjects achieving an HI antibody 
titer  1:40.  A saline placebo may be an acceptable control if the population 
studied is not a group for whom seasonal influenza vaccination is routinely 
recommended by the ACIP due to increased risk of complications from 
influenza illness or if the study is conducted off-season.  If a study is 
conducted just prior to the influenza season in populations who are at 
increased risk from influenza illness, use of a U.S. licensed influenza vaccine 
as a control may be appropriate.  The purpose of the control arm in this type 
of study design, whether it is a saline-placebo or a U.S. licensed influenza 
vaccine, is primarily to provide a comparative assessment of safety and to 
provide a general assurance of immunogenicity response from the new 
vaccine.  
9  Contains Nonbinding Recommendations 
 
For example, the following recommendations, which have been modified 
from guidelines by the currently-titled, Committee for Medicinal Products 
for Human Use of the European Medicines Agency (Ref. 14), may support 
an accelerated approval.   
 
For adults < 65 years of age and for the pediatric population: 
 
  The lower bound of the two-sided 95% CI for the percent of subjects 
achieving seroconversion for HI antibody should meet or exceed 40%. 
 
  The lower bound of the two-sided 95% CI for the percent of subjects 
achieving an HI antibody titer  1:40 should meet or exceed 70%. 
 
For adults  65 years of age: 
 
  The lower bound of the two-sided 95% CI for the percent of subjects 
achieving seroconversion for HI antibody should meet or exceed 30%. 
 
  The lower bound of the two-sided 95% CI for the percent of subjects 
achieving an HI antibody titer  1:40 should meet or exceed 60%. 
 
c.  Alternative study designs that assess different endpoints and/or other immune 
responses will be reviewed by CBER and may be accepted in support of an 
accelerated approval.  CBER would need to determine that the study design is 
acceptable and the proposed surrogate endpoint(s) is reasonably likely to 
predict clinical benefit. 
 
2.  Safety 
 
Safety data must be collected from subjects enrolled in pre-licensure clinical trials 
intended to support the accelerated approval of a new seasonal inactivated 
influenza vaccine (21 CFR 312.23, 312.32, 312.56, 312.60 and 312.62).  The 
monitoring of these subjects should follow the outline for safety evaluations 
described in Section III.A.3. above.  A total safety database large enough to rule 
out a serious adverse event that occurs at a rate of 1 in 300 may be sufficient 
when a sponsor has adequate marketing and safety experience with the same 
manufacturing process for a seasonal vaccine licensed outside the United States 
and these data are presented in the BLA and assessed as such.  For example, the 
upper limit of the two-sided 95% CI of the true serious adverse event rate is 
0.0032 (<1 in 300) when no serious adverse event is observed among 1150 
subjects who received vaccine in clinical trials, using the Clopper-Pearson 
method.  However, the size of the pre-licensure safety database, especially for 
seasonal influenza vaccines manufactured using novel processes such as cell-
culture and for seasonal influenza vaccines that contain novel adjuvants, would be 
influenced by factors such as the nature of the new manufacturing process and 
available pre-clinical and clinical data, and should be discussed with CBER.   
10  Contains Nonbinding Recommendations 
 
Moreover, if a serious adverse event is present in a safety database of about 1,000 
subjects, and there is concern that it may be vaccine-related, additional safety data 
may be needed.  Safety data to support use in pediatric populations would also be 
needed and should be submitted either as part of the BLA, or as a clinical efficacy 
supplement at a later time, if pediatric studies are deferred under PREA (see 
Section III.C.4.  Pediatric Research Equity Act). 
 
3.  Postmarketing Confirmatory Studies 
 
For the design of postmarketing studies the sponsor should refer to studies 
described in Section III.A.1. on effectiveness data to support traditional approval 
of new seasonal inactivated influenza vaccines.  
 
C.  Additional Considerations 
 
1.  Types of Influenza Vaccines 
 
U.S. licensed seasonal inactivated influenza vaccines include those that are 
propagated in embryonated chicken eggs, and the virus is disrupted in the 
manufacturing process yielding split virus inactivated vaccines.  The current 
recommendations regarding clinical effectiveness and safety data to support 
licensure apply to both nonadjuvanted and adjuvanted hemagglutinin-based 
seasonal vaccines, including split virus, subunit, and whole virus inactivated 
vaccines propagated in embryonated chicken eggs  or cell-culture, and to 
recombinant hemagglutinin-based protein, and DNA vaccines that express 
hemagglutinin.  Of note, vaccines manufactured by processes different from those 
used for currently licensed vaccines in the United States will likely require 
different pre-clinical evaluations.  Detailed information on product characteristics 
and manufacturing processes are needed for all new vaccines, regardless of their 
derivation (see footnote 1). 
 
2.  Clinical Lot Consistency 
 
The objective of a clinical lot consistency study is to show consistency of 
manufacturing and performance of the final product by demonstrating that three 
consecutively manufactured final formulated bulk lots of vaccine elicit equivalent 
immune responses.  The HI antibody assay may be used to assess the immune 
responses.  We recommend a pair-wise comparison of the 95% CI on the ratio of 
GMTs for each viral strain contained in the three vaccine lots as an appropriate 
primary endpoint.  The two-sided 95% CI on the GMT ratio should be entirely 
within 0.67 and 1.5.  Seroconversion rates for the HI antibody response to each of 
the viral strains contained in the vaccine may be assessed as secondary endpoints.  
Assessment of lot consistency may be incorporated in studies designed to support 
the accelerated approval of a new influenza vaccine.   
 
 
11  Contains Nonbinding Recommendations 
 
 
We may decide, on a case by case basis, that lot consistency may be evaluated 
and incorporated in the postmarketing commitment studies.  This determination 
would be influenced by factors such as the manufacturing process used for the 
new influenza vaccine and available manufacturing and clinical experience.  
 
3.  Adjuvanted Seasonal Inactivated Influenza Vaccines 
 
An effective adjuvant might reduce the amount of antigen needed to elicit 
protective immune responses and may also have other desirable properties such as 
cross protection against evolving influenza viral strains.  However, vaccine 
formulations containing adjuvants may pose additional safety risks.   
 
Data supporting the safety of the adjuvanted formulation and added benefit over 
the unadjuvanted formulation must be submitted in the BLA (42 U.S.C. 
262(a)(2)(C)(i); 21 CFR 601.2).  At an early stage of development, clinical data 
supporting the value of adding the adjuvant should be provided, such as evidence 
of enhanced immune response, antigen-sparing effects, or other advantages, as 
should data supporting selection of the dose of the adjuvant itself.  Safety 
information in the BLA may include the safety experience obtained from 
domestic or foreign trials.  Safety experience with the same adjuvant formulated 
with other vaccine antigens may also contribute to the adjuvants safety 
evaluation.  It is expected that nonclinical and clinical information needed to 
support the safety of the adjuvant will be discussed with us early in development.  
Finally, to delineate additional information about the adjuvanted vaccines safety 
profile, we may seek agreement from sponsors to conduct certain postmarketing 
studies. 
 
  Dose and Formulation Selection 
 
Assuming that the vaccine is a hemagglutinin-based product, the HI 
antibody assay may be appropriate to evaluate the immune response.  
 
For initial dose and formulation selection, a comparative clinical study of 
adjuvanted vs. non-adjuvanted vaccines that both contain the same amount 
of antigen should demonstrate that the immune response elicited by the 
adjuvanted antigen is better than that elicited by the same antigen alone.  
For differences in HI antibody titer and seroconversion rates, the lower 
confidence limit on the appropriate point estimate excluding equality (i.e., 
the value 1 for the ratio parameter or 0 for a difference parameter) may be 
sufficient to demonstrate the added value of the adjuvant.  
 
In the setting of a shortage for seasonal influenza vaccines, defined in 
Section II, use of an adjuvant may be supported by data from a 
comparative study demonstrating non-inferiority immune responses  
12  Contains Nonbinding Recommendations 
 
elicited by the adjuvanted vaccine containing a lower amount of antigen  
than the dose-optimized non-adjuvanted vaccine formulation.  Other 
approaches may be possible, and we encourage you to discuss your 
proposal(s) with us. 
 
Selection of an appropriate dose and formulation should also be guided by 
the safety profile of the formulations and regimens being studied. 
   
  Adding an Adjuvant to a Licensed Seasonal Influenza Vaccine 
 
If an adjuvant is added to a licensed seasonal influenza vaccine for use 
without antigen sparing effects (i.e., the dose of the antigen is not 
changed), the immune response elicited by the adjuvanted vaccine 
formulation should be substantially better than that elicited by the 
unadjuvanted vaccine for the study population.  A comparative clinical 
trial may first be done under accelerated approval using immunogenicity 
endpoints, followed by a confirmatory postmarketing study of 
comparative effectiveness in that study population.  For accelerated 
approval, meaningful differences in HI antibody titer and seroconversion 
rates between adjuvanted and unadjuvanted formulations should be 
specified and justified.  Meaningful differences may also include a 
demonstration of cross-reactivity against drifted strains.  For confirmatory 
postmarketing studies, meaningful differences in clinical endpoints should 
be specified and justified. 
 
4.  Pediatric Research Equity Act 
 
The Pediatric Research Equity Act of 2003 (PREA) (Public Law 108-155) 
(section 505B of the Federal Food, Drug, and Cosmetic Act, 21 U.S.C.  355c) 
addresses drug and biological product development for pediatric uses.  All 
sponsors have obligations to study pediatric populations as outlined in PREA.  
Under PREA, all applications (or clinical efficacy supplements) submitted under 
section 505 of the Federal Food, Drug, and Cosmetic Act (the Act) (21 U.S.C. 
355) or section 351 of the Public Health Service Act (PHS Act) (42 U.S.C. 262) 
for a new active ingredient, new indication, new dosage form, new dosing 
regimen, or new route of administration are to contain a pediatric assessment 
(pediatric clinical data) unless the sponsor has obtained a waiver or deferral from 
FDA (21 U.S.C. 355c).  A draft guidance on the implementation of PREA was 
issued by FDA in September 2005 (Ref. 16).  As stated in that document, FDA 
encourages the submission of pediatric development plans to FDA as early as 
possible in the vaccine development process.  
 
13  Contains Nonbinding Recommendations 
 
5.  Postmarketing Evaluations 
 
As part of your BLA submission, you should include a pharmacovigilance plan, 
especially if the vaccine involves novel manufacturing processes and/or novel 
adjuvants.  The format of these submissions should be in accordance with the 
International Conference on Harmonisation of Technical Requirements for 
Registration of Pharmaceuticals for Human Use (ICH E2E guidance) (Ref. 17).   
 
In addition, routine pharmacovigilance should include submission of adverse 
event reports to the Vaccine Adverse Event Reporting System in accordance with 
21 CFR Part 600, Subpart D.  You may be requested to consider expedited 
reporting of some adverse event reports (e.g., serious labeled adverse events) and 
dose distribution data for the vaccine. 
 
 
14  Contains Nonbinding Recommendations 
 
IV.  REFERENCES 
 
1.  World Health Organization.  WHO guidelines on nonclinical evaluation of vaccines. 
Annex 1.  WHO Technical Report Series.  2005;927:31-63. 
www.who.int/biologicals/publications/trs/areas/vaccines/nonclinical_evaluation/en/. 
 
2.  Lamb RA, Krug RM.  Orthomyxoviridae:  The Viruses and Their Replication.  In:  Fields 
Virology, Editors-in-Chief:  Knipe DM and Howley PM.  4th Edition. Philadelphia, PA: 
Lippincott Williams and Wilkins, Publishers; 2001;1487-1531. 
 
3.  Palese P, Garcia-Sastre A.  Influenza vaccines:  present and future.  The Journal of 
Clinical Investigation.  2002;110:9-13. 
 
4.  Nakajima S, Nobusawa E, Nakajima K.  Variation in response among individuals to 
antigenic sites on the HA protein of human influenza virus may be responsible for the 
emergence of drift strains in the human population.  Virology.  2000;274:220-231. 
 
5.  Holmes EC, Ghedin E, Miller N, Taylor J, Bao Y, St. George K, Grenfell BT, Salzberg 
SL, Fraser CM, Lipman DJ, Taubenberger JK.  Whole-genome analysis of human 
influenza A virus reveals multiple persistent lineages and reassortment among recent 
H3N2 viruses.  PLoS Biology.  2005;3:1579-1589. 
 
6.  Barr IG, Komadina N, Hurt AC, Iannello P, Tomasov C, Shaw R, Durrant C, Sjogren H, 
Hampson AW.  An influenza A(H3) reassortant was epidemic in Australia and New 
Zealand in 2003.  Journal of Medical Virology.  2005;76:391-397. 
 
7.  Centers for Disease Control and Prevention.  Prevention and Control of Influenza: 
Recommendations of the Advisory Committee on Immunization Practices (ACIP).  
MMWR Morbidity and Mortality Weekly Report.  1997;46(RR-9):1-25. 
 
8.  Centers for Disease Control and Prevention.  Prevention and Control of Influenza. 
Recommendations of the Advisory Committee on Immunization Practices (ACIP).  
MMWR Morbidity and Mortality Weekly Report.  2000;49(RR-3):1-38. 
 
9.  Centers for Disease Control and Prevention.  Prevention and Control of Influenza. 
Recommendations of the Advisory Committee on Immunization Practices (ACIP).  
MMWR Morbidity and Mortality Weekly Report.  2006;55(RR-10):1-42.  Erratum: 
2006;55(29) 800. 
 
10. Centers for Disease Control and Prevention.  Update:  Influenza Vaccine Supply and 
Recommendations for Prioritization During the 2005--06 Influenza Season.  MMWR 
Morbidity and Mortality Weekly Report.  2005;54(34);850:1-3. 
 
15  Contains Nonbinding Recommendations 
 
11. Testimony of Julie L. Gerberding, M.D., M.P.H., Director, Centers for Disease Control 
and Prevention, on Protecting the Publics Health:  CDC Influenza Preparedness 
Efforts before The Committee on Government Reform, U.S. House of Representatives, 
2/12/2004. 
 
12. Hobson D, Curry RL, Beare AS, Ward-Gardner A.  The role of serum 
haemagglutination-inhibiting antibody in protection against challenge infection with 
influenza A2 and B viruses.  Journal of Hygiene, (Camb).  1972;70:767-777. 
 
13. de Jong JC, Palache AM, Beyer WEP, Rimmelzwaan GF, Boon ACM, Osterhaus 
ADME.  Haemagglutination-inhibiting antibody to influenza virus.  Developmental 
Biology (Basel).  2003;115:63-73. 
 
14. Committee for Proprietary Medicinal Products (CPMP).  Note for guidance on 
harmonisation of requirements for influenza vaccines.  CPMP/BWP/214/96.  The 
European Agency for the Evaluation of Medicinal Products (EMEA), March 1997. 
 
15. Treanor J, Keitel W, Belshe R, Campbell J, Schiff G, Zangwill K, Wolff M, Klimov A, 
Levandowski R, Lambert L.  Evaluation of a single dose of half strength inactivated 
influenza vaccine in healthy adults.  Vaccine.  2002;20:1099-1105. 
 
16. FDA Draft Guidance for Industry:  How to Comply with the Pediatric Research Equity 
Act, September 2005 (http://www.fda.gov/cber/gdlns/pedreseq.htm).  This draft 
guidance, when finalized, will represent FDAs current thinking on that topic. 
 
17. ICH Guidance for Industry:  E2E Pharmacovigilance Planning, April 2005 
(http://www.fda.gov/cber/gdlns/ichpvp.htm).  
 
 
 
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