Guiding Principles for Development of ACIP Recommendations for 

Vaccination during Pregnancy and Breastfeeding 

April 2008 

Advisory Committee on Immunization Practices 

Workgroup on the Use of Vaccines during Pregnancy and Breastfeeding 
Guiding principles for development of ACIP recommendations for vaccination during breastfeeding and pregnancy 

Guiding principles for developing ACIP recommendations for vaccination during 

pregnancy and breastfeeding 

April 10, 2008 

Formulating policy to guide vaccination of women during pregnancy and breastfeeding is 

challenging because the evidence-base to guide decisions is extremely limited. In the past, ACIP 

has not provided guidance to workgroups on either the process to formulate policy for this 

population or the format and language for recommendations. As a result, workgroups have taken 

a variety of approaches to considering and presenting the issues, resulting in a diversity of 

recommendations that vary in clarity and underlying rationale. . The principles presented here 

provide guidance to help standardize both the process of policy formulation and the format and 

language of recommendations for pregnant and breastfeeding women. All ACIP statements 

about vaccines and other biologics for use in adolescents or adults should include a background 

section on vaccination during pregnancy and breastfeeding and provide explicit pregnancy and 

breastfeeding recommendations using standardized language as outlined below. To arrive at 

pregnancy and breastfeeding recommendations, ACIP workgroups or subject matter experts 

charged with developing vaccine statements should review the process suggestions outlined 

below. These suggestions, while similar to the process generally followed by workgroups, focus 

specifically on issues related to pregnancy, breastfeeding and decision making in the absence of 

a strong evidence-base. 

1. This document and appendix provide a brief overview of specific issues related to 

vaccination during pregnancy and breastfeeding 

2. Guidance for the pregnancy and breastfeeding background section 

a. Title: “Vaccination of women during pregnancy and breastfeeding” 

b. Scope: This section should address the following core topics with a narrow focus 

on the vaccine product/s in question 

i. Disease burden: pregnant women, fetus, newborns and young infants 

ii. Vaccination during pregnancy 

1. Objective and rationale: (clear statement of the primary 

objective(s): to protect mother and/or fetus and/or neonate and/or 

young infant ) 

2. Immunogenicity data (mother; neonate and young infant if 

available) 

3. Efficacy data (mother; neonate and young infant if available) 

4. Safety data (mother; fetus, neonate and young infant if available) 

5. Pregnancy trimester-specific issues (safety, efficacy, other) 

iii. Vaccination during breastfeeding 

1. Objective and rationale: (clear statement of the primary 

objective(s): to protect mother and/or neonate and/or young infant 

and/or future offspring) 

2. Efficacy 

3. Safety 

4. Timing (eg, immediately post-partum or later in infancy; with 

respect to the infant/childhood vaccine series) 

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Guiding principles for development of ACIP recommendations for vaccination during breastfeeding and pregnancy 

iv. Cost-effectiveness (only if there are unique issues related to vaccine use 

during pregnancy/breastfeeding) 

v. Alternatives or adjuncts to vaccination during pregnancy 

vi. Logistics (eg, vaccination record) and coadministration with other 

vaccines 

vii. Areas for future research (could highlight important, feasible studies that 

would assist vaccine policy decisions) 

c. Length: the section should be short for most vaccine products 

d. Data sources: indicate types of studies including well controlled clinical trials, 

observational studies, reviews of published literature, and unpublished data 

3. Guidance for the pregnancy/breastfeeding recommendations 

a. These recommendations should be integrated into the recommendations section of 

the document rather than presented separately (as suggested for the 

pregnancy/breastfeeding background). Explicit recommendations should be 

provided both for vaccination during pregnancy and during breastfeeding 

b. Recommendations should reference the pregnancy/breastfeeding background 

section for rationale and other details 

c. Pregnancy and breastfeeding recommendations should appear in the “special 

populations” section of the recommendations. If pregnancy or breastfeeding are 

deemed precautions or contraindications, recommendations should instead appear 

in the “precautions/contraindications” section, and the special populations section 

should refer readers to the precautions/ contraindications section. 

d. Recommendations should specify 

i. Precautions/contraindications for the pregnant and breastfeeding 

populations 

ii. Timing of vaccination 

1. During pregnancy: pregnancy trimester 

2. During breastfeeding: any specific time periods to aim for or avoid 

iii. Minimum time period between vaccination and becoming pregnant, if 

vaccination is a precaution or contraindication 

4. Guidance on language to reduce unnecessary variation across statements 

a. Pregnancy/breastfeeding background section 

i. For each topic heading listed in 2b, lack of data should be stated explicitly 

where it applies. 

ii. For safety, absence of adequate study/surveillance/follow up should be 

distinguished clearly from absence of adverse events 

b. Recommendations section: 

i. General 

 Distinguish clearly between contraindications and precautions. ACIP 

definitions are as follows: 

Contraindication: A condition in a recipient that increases the risk for a 

serious adverse reaction. A vaccine will not be administered when a 

contraindication is present 

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Guiding principles for development of ACIP recommendations for vaccination during breastfeeding and pregnancy 

Precaution: A condition in a recipient that might increase the risk for a 

serious adverse reaction or that might compromise the ability of the vaccine 

to produce immunity. Under usual circumstances, vaccination should be 

deferred. However, vaccination might be indicated because benefits 

outweigh risks 

In the context of pregnancy and breastfeeding, serious adverse reaction 

includes maternal, fetal or neonatal serious adverse events linked to the 

vaccine. Contraindication means that there is direct evidence or strong 

biologic plausibility and suggestive evidence that the risk of severe adverse 

event is elevated for at least one of these groups. Precaution means there is 

no supporting evidence but there is some biologic plausibility; precaution 

may also mean that there is a lack of data to support safety. 

ii. Standard language: Choose which best applies and modify language only 

if necessary 

1. Pregnancy recommendations 

1. “Vaccination of pregnant women is recommended; all 

pregnant women should be vaccinated” 

Illustrative examples: Inactivated influenza vaccine

2. “Pregnancy is not a contraindication or precaution to 

vaccination; routine vaccination recommendations should 

be applied to pregnant women” 

Illustrative examples: Tetanus-diphtheria (Td), Hepatitis B, 

Meningococcal polysaccharide 

3. “Pregnancy is a precaution and under normal circumstances 

vaccination should be deferred; vaccine should only be 

given when benefits outweigh risks” 

Illustrative examples: Hepatitis A , IPV, or yellow fever (in 

case of travel to an area where exposure is likely); rabies (eg, 

after a possible exposure) 

4. “Pregnancy is a contraindication to vaccination; vaccine 

should not be administered to pregnant women. 

Vaccination with contraindicated vaccines during 

pregnancy is not ordinarily a reason for pregnancy 

termination” 

Illustrative examples: MMR, varicella, live-attenuated 

influenza vaccine 

2. Timing of vaccination during pregnancy 

1. “Vaccination can be given at any time during pregnancy” 

2. “Vaccination should be deferred until X trimester of 

pregnancy unless there is a specific indication for 

vaccination early in pregnancy that outweighs risks” 

3. “Vaccine should not be administered during X trimester of 

pregnancy” 

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Guiding principles for development of ACIP recommendations for vaccination during breastfeeding and pregnancy 

4. For vaccines where pregnancy is a contraindication: 

“Women should avoid becoming pregnant until 28 days 

after vaccination” 

i. Note: 28 days is the time period that applies to most 

currently contraindicated vaccines; however if for a 

particular vaccine product there is evidence for a 

shorter or longer time period, the 28 days may be 

modified as needed. 

3. Breastfeeding recommendations 

1. “Breastfeeding is not a contraindication or precaution to 

vaccination; routine vaccination recommendations should 

be applied” 

Illustrative examples: Current recommendations appear to 

place all vaccines except smallpox in this category (although 

the language is not clear) 

2. “Breastfeeding is a precaution and under usual 

circumstances vaccination should be deferred; vaccine 

should only be given when benefits outweigh risks” 

3. “Breastfeeding is a contraindication to vaccination; vaccine 

should not be administered to breastfeeding women.” 

Illustrative example: smallpox vaccine 

4. Timing of vaccination during breastfeeding 

1. “Vaccination is recommended before postpartum hospital 

discharge for all women whether or not they intend to 

breastfeed” 

2. “Vaccine may be administered at any time postpartum, for 

all women whether or not they intend to breastfeed” 

3. “Where possible, vaccination of breastfeeding women 

should be deferred until X period postpartum, unless 

benefits outweigh risks” 

4. “For breastfeeding women, vaccine should not be 

administered during X period postpartum” 

5. Suggestions to aid policy decision-making in the absence of adequate data 

a. Review any unpublished or pre-licensure data available (eg, from accidental 

vaccinations of pregnant women) 

b. Assess whether there will be adequate data in the future and on what timeline 

c. Review the decisions of other professional organizations/ other countries and the 

underlying rationale 

d. Review “ACIP precedents” with regards to vaccination during pregnancy and 

breastfeeding 

i. Vaccination during breastfeeding is contraindicated only for smallpox 

vaccine 

ii. Live vaccines pose theoretical concern more often than inactivated 

vaccines 

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Guiding principles for development of ACIP recommendations for vaccination during breastfeeding and pregnancy 

iii. When risk of maternal infection is high and risk of a poor outcome is high, 

vaccination is recommended (eg, rabies, yellow fever) 

iv. In the absence of adequate safety and efficacy data, direct protection of 

mother provides a stronger basis than indirect protection of neonate/ 

young infant for a recommendation of vaccination during pregnancy 

v. There is more comfort with second and third trimester vaccination than 

first trimester (not based on safety data, but based on public perception) 

e. Evaluate safety checks in place in case the pregnancy/breastfeeding 

recommendations for the product in question result in unintended adverse 

consequences 

i. Is post-licensure data on safety (passive, or active, or special studies) 

likely to detect important adverse events? 

ii. Are there registries or other sources that would allow for detection of 

safety or efficacy concerns? 

iii. If there are concerns about maternal antibody inhibition of infant response 

to a similar vaccine or fetal antigen tolerance with subsequent diminished 

postnatal responsiveness, is any system in place to monitor those 

outcomes? 

iv. Are there any sentinel events of concern that warrant particular attention? 

6. Suggestions on how to standardize the gathering of expert opinion 

i. Areas of expertise that should be represented in workgroup deliberations: 

1. Disease burden (all relevant populations (eg, pregnant women, 

neonates, young infants) 

2. Vaccine product: efficacy, safety for pregnant women, fetus, 

newborn/infant as relevant 

3. Maternal/neonatal immunology if concerns about maternal antibody 

inhibition of infant immune response to same or related vaccine are 

relevant 

4. Consider: target population representation (eg, pregnant woman; a 

representative of infants who have been affected by the disease in 

question) 

5. Scientific leader from obstetric clinical community 

6. Scientific leader from pediatric clinical community 

7. Consider: inclusion of someone with expertise in health law 

ii. Strategies for obtaining input 

1. If some members are particularly vocal or stifling of free 

conversation, consider solicitation of written input through a 

standard set of key questions from all members 

2. Consider pulling in additional targeted experts if a particular issue 

stands out as complex or controversial 

iii. Suggestion of procedures to follow when expert opinion cannot reach 

consensus 

1. Present pros and cons as options to the full ACIP, with a summary of 

supporting evidence, and let them vote 

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Guiding principles for development of ACIP recommendations for vaccination during breastfeeding and pregnancy 

2. Allow the workgroup to draft a dissenting opinion and present both 

positions to ACIP before they vote 

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Guiding principles for development of ACIP recommendations for vaccination during breastfeeding and pregnancy 

Appendix: Brief overview of issues related to vaccination during pregnancy and 

breastfeeding 

1. Vaccination during pregnancy 

a. Vulnerable populations 

i. Pregnant women 

1. Altered immune response 

2. Increased risk of some infections 

3. Increased risk of severe outcomes (maternal, fetal or both) of some

infections 

ii. Fetus, newborn, young infant 

1. Immature immune response 

2. Increased risk of some infections 

3. Increased risk of severe outcomes of some infections 

4. Infection sequelae can result in lifelong disability 

b. The promise of vaccination during pregnancy (any or all of the below) 

i. Protection of mother 

ii. Protection of fetus 

iii. Protection of neonate 

iv. Protection of young infant 

v. In the US there are approximately 4 million live births each year 

vi. In the US >98% of women have at least 1 prenatal visit, providing a health 

care opportunity for vaccination 

c. Concerns about vaccination of pregnant women 

i. Lack of data to make evidence-based decisions 

1. No or limited well-controlled trials to establish efficacy of vaccines 

in pregnant women or their offspring 

2. No or limited post-licensure studies of efficacy or safety (eg, from 

registries, VAERS, Vaccine Safety Datalink) 

3. No or limited animal data 

4. No or limited data on burden of illness 

o Key aspects of interest: incidence, severity, sequelae, time 

period of most vulnerability to infection 

o Key target populations: pregnant woman, fetus, newborn, 

young infant 

ii. Theoretical concerns about efficacy (woman, fetus, newborn) 

1. Will altered immune status of pregnant woman reduce response to 

vaccine? 

2. Will sufficient maternal antibody be transferred to fetus to confer 

protection (to fetus, newborn)?

3. Will half life of maternal antibody be sufficient to protect 

fetus/newborn during relevant period of vulnerability? 

iii. Theoretical concerns about safety (woman, fetus, newborn) 

1. Vaccine type 

o Live vaccines (eg, viral antigen) historically have been 

viewed as more risky than inactivated and toxoid vaccines 

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Guiding principles for development of ACIP recommendations for vaccination during breastfeeding and pregnancy 

i. There is evidence of fetal vaccinia infection 

following smallpox vaccination during pregnancy 

ii. There is no direct evidence of any live vaccine 

resulting in a fetal or neonatal serious adverse event 

o Even more limited data on newer vaccine types 

i. Unclear that generalizations about live vs. 

inactivated vaccines can be applied to new or future 

vaccine antigen types and technologies 

ii. Unclear that generalizations about live parenteral 

vaccines can be applied to live mucosal vaccines 

2. Additives/adjuvants/preservatives (eg, thimerosal) 

o Limited or no safety data on exposure of pregnant women, 

fetus and newborn to these 

3. Timing of vaccination 

o Safety risks may vary with time period of vaccination 

during pregnancy (eg, early pregnancy vs. late pregnancy; 

immediately post-partum vs. later) 

iv. Concerns about impaired newborn/infant immune response to childhood 

series 

1. Primary concern is inhibition of newborn or infant response to active 

vaccination due to high concentratons of passively acquired maternal 

antibodies 

2. Evidence that transplacental transfer of maternal antibody can 

interfere with infant response to childhood vaccine series 

o naturally-acquired or vaccine-induced maternal measles 

antibody interferes with infant response to measles vaccine 

3. Theoretic concern that vaccination during pregnancy could similarly 

impair response to routine childhood series 

o Extent of inhibition depends on multiple factors (eg, type of 

maternal and infant vaccine antigen, concentration and 

avidity of maternal antibody, timing and doses in infant 

series) 

o Priming of the infant immune system can occur despite 

presence of maternal antibody 

4. In addition to concerns about maternal antibody inhibition of infant 

postnatal responses to infant immunization series, there are also 

theoretical concerns that the fetus could develop antigen tolerance in 

utero which may result in diminished postnatal responsiveness to the 

infant immunization series. 

v. Lack of harmonization with FDA labeled indications (see Table for a 

description of FDA pregnancy categories) 

1. Label subject to federal regulations

o 21 CFR 201.56 (General) and 201.57 (Specific) 

2. One currently licensed vaccine (HPV) is pregnancy category B 

3. One currently licensed vaccine (anthrax) is pregnancy category D 

4. All other licensed vaccines are currently labeled as category C 

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Guiding principles for development of ACIP recommendations for vaccination during breastfeeding and pregnancy 

vi. Public perception/risk communication 

1. Temporal association between vaccine and adverse pregnancy events 

2. Principle of avoiding any unnecessary exposures during pregnancy 

vii. Legal liability 

1. National Childhood Vaccine Injury Act 

o If covered vaccine properly prepared and accompanied by 

proper directions and warnings, manufacturer cannot be 

held liable for injuries. 

o Law clearly covers vaccine directly administered to child 

o Statute is silent on in utero transmission (eg, adverse effect 

in fetus whose mother is vaccinated); case law is unclear 

viii. Logistical concerns 

1. Most obstetric offices do not have the infrastructure (eg, proper 

storage refrigerator, tracking of administration documentation 

required by law) to administer vaccines and obstetric providers often 

do not view vaccination as their primary responsibility 

2. There is no good vaccine record keeping system for adult 

vaccination (eg, to avoid problem of repeat vaccination) 

3. Providers who care for pregnant women are often most concerned 

about the woman and fetus and may be less educated/aware about 

infectious risks to the neonate and young infant 

4. Vaccine recommendations for pregnant women have a history of 

lack of clarity 

d. Alternatives or supplements to vaccination during pregnancy: Depending on the 

infection, some or all of the below may be effective as adjuncts or as alternatives 

i. Routine infection control (eg, hand hygiene, respiratory etiquette) 

ii. Vaccination of household contacts of newborns/pregnant women (“cocoon 

strategy” for pertussis and influenza) but limited data on efficacy 

iii. Postpartum vaccination (See section 2 below) 

1. Eg, rubella and Tdap vaccination recommendation 

2. Avoids safety concerns of vaccination during pregnancy 

3. Only confers fetal protection in subsequent pregnancies (assuming 

maternal antibody levels persist at adequate concentrations) 

4. Only confers maternal protection after the time of vaccination (eg, 

misses vulnerable time window of that pregnancy and early 

postpartum period) 

2. Vaccination during breastfeeding 

i. Objectives 

1. Protect mother from vaccine-preventable diseases 

2. Indirect protection of neonate/ infant by preventing infection in 

mother (“cocoon strategy”; see 1d) 

3. Confer protection in subsequent pregnancies (eg, rubella) 

4. Transfer of protective antibody to neonate/ infant 

o Antibody in human milk is >90% secretory IgA 

o Offers surface protection in the mouth 

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Guiding principles for development of ACIP recommendations for vaccination during breastfeeding and pregnancy 

o Unclear whether offers additional protection (eg, against 

respiratory infection) 

o Transfer of circulatory IgG to infant has not been 

documented 

ii. Concerns 

1. Interruption of breastfeeding (which has known, important benefits) 

2. Interference of antibody transferred via human milk with 

neonate/infant direct response to childhood series 

o A particular issue for orally administered vaccines 

o Evidence from rotavirus and poliovirus vaccines suggest 

this may be overcome by administering >1 dose 

3. Transmission of vaccine virus in the case of live vaccines 

o Evidence from smallpox, MMRV, MMR 

4. Consistency with FDA labels 

o Majority of labels state “Because many drugs are excreted 

in human milk, caution should be exercised when 

administering vaccine to a nursing woman” 

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Guiding principles for development of ACIP recommendations for vaccination during breastfeeding and pregnancy 

Table. Food and Drug Administration pregnancy categories*. Regulation requires that each 

product be classified under one of five pregnancy categories (A, B, C, D, or X), on the basis of 

risk of reproductive and developmental adverse effects or, for certain categories, on the basis of 

such risk weighed against potential benefit. 

Pregnancy category A Adequate and well controlled studies in 

women fail to demonstrate a risk to the fetus in 

the first trimester (and there is no evidence of a 

risk in later trimester), and the possibility of 

fetal harm appears remote. 

Pregnancy category B Animal reproduction studies have failed to 

demonstrate a risk to the fetus and there are no 

adequate and well-controlled studies in 

pregnant women OR Animal studies have 

shown an adverse effect, but adequate and 

well-controlled studies in pregnant women 

have failed to demonstrate a risk to the fetus 

during the first trimester (and there is no 

evidence of risk in later trimesters) 

Pregnancy category C Animal reproduction studies have shown an 

adverse effect on the fetus and there are no 

adequate and well-controlled studies in 

humans, but potential benefits may warrant use 

of the drug in pregnant women despite 

potential risks OR Animal reproduction studies 

have not been conducted and there are no 

adequate and well-controlled studies in humans

Pregnancy category D There is positive evidence of human fetal risk 

based on adverse reaction data from 

investigational or marketing experience or 

studies in humans, but potential benefits may 

warrant use of the drug in pregnant women 

despite potential risks. 

Pregnancy category X Studies in animals or humans have 

demonstrated fetal abnormalities and/or there 

is positive evidence of human fetal risk based 

on adverse reaction data from investigational 

or marketing experience, and the risks involved 

in use of the drug in pregnant women clearly 

outweigh potential benefits. 

*Note: As of January, 2008, FDA is in the process of developing a new pregnancy labeling 

system. This new system is under consideration and has not yet been instituted. 

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ACIP Workgroup on Use of Vaccines during Pregnancy and Breastfeeding 

Members 

ACIP Members 

Carol J. Baker, MD Kathleen Neuzil, MD, MPH 

Professor of Pediatrics Partnership for Appropriate Techonology in 

Molecular Virology and Microbiology Health (PATH) 

Baylor College of Medicine University of Washington, Seattle, WA 

Houston, TX 

ACIP Ex Officio Members 

Marion Gruber, PhD Indira Jevaji, MD, MSL, FAAP 

Associate Director for Regulatory Policy Medical Officer 

Office of Vaccines Research and Review Division of Vaccine Injury Compensation 

Center for Biologics Evaluation and Research Health Resources and Service Administration 

Food and Drug Administration, DHHS DHHS 

ACIP Liaison Organization Representatives 

American Academy of Family Physicians American College of Obstetricians and 

Douglas Campos-Outcalt, MD, MPA Gynecologists

Associate Head Stanley Gall, MD 

Department of Family & Community Professor of Obstetrics, Gynecology and 

Medicine Women`s Health Professor of Public Health 

University of Arizona College of Medicine, and Information Science 

Phoenix, AZ University of Louisville 

Louisville, KY 

American Academy of Pediatrics, Committee 

on Infectious Diseases

David Kimberlin, MD 

Committee on Infectious Diseases 

University of Alabama at Birmingham 

Division of Pediatric Infectious Diseases 

Birmingham, AL 

Other Representatives and Subject Matter Experts 

Stephanie Schrag, DPhil Kevin Ault, MD 

Epidemiology Team Lead Associate Professor 

Respiratory Diseases Branch Department of Gynecology and Obstetrics 

NCIRD, CDC Emory University School of Medicine 

69 Jesse Hill Jr. Drive, S.E. 

Atlanta, Georgia
Guiding principles for development of ACIP recommendations for vaccination during breastfeeding and pregnancy 

George M. Carlone, PhD 

Chief, Immunology Laboratories 

Meningitis and Vaccine-Preventable Diseases 

Branch 

Division of Bacterial Diseases 

Janet Cragan, MD, MPH 

National Center on Birth Defects and 

Developmental Disabilities 

CDC 

Anthony Fiore, MD, MPH 

Medical Epidemiologist 

Influenza Division 

NCIRD, CDC 

Julianne Gee, MPH 

Epidemiologist, Immunization Safety Office 

CDC 

Diane Hoffman, MS, JD 

Associate Dean for Academic Programs 

Director, Law and Health Care Program and 

Professor of Law 

University of Maryland, Baltimore, MD 

Megan C. Lindley, MPH 

Immunization Services Division 

NCIRD, CDC 

Gina T. Mootrey, DO, MPH 

Associate Director for Adult Immunization 

Immunization Services Division 

NCIRD, CDC 

Lauri Markowitz, MD 

Medical Epidemiologist 

Division of STD Prevention 

NCHHSTP, CDC 

Nancy E. Messonnier, MD 

Chief, Meningitis and Vaccine Preventable 

Diseases Branch 

Division of Bacterial Diseases 

NCIRD, CDC 

Susan Reef, MD 

Medical Epidemiologist 

Global Immunization Division 

NCIRD,CDC 

Fran A. Rubin, Ph.D. 

Program Officer for Group A streptococci, 

Group B streptococci, Maternal 

Immunization 

Respiratory Diseases Branch 

Division of Microbiology and Infectious 

Diseases 

National Institute of Allergy and Infectious 

Diseases 

Judy V. Schmidt, RN, MSN, MA, Ed.D. 

Liaison for ISD to ACOG 

Public Health Educator 

Education, Information, and Partnership 

Branch, Immunization Services Division 

NCIRD, CDC 

Tami Skoff, MS 

Epidemiologist 

Division of Bacterial Diseases 

NCIRD, CDC 

Barbara Slade, MD, MS 

CISA Team Lead 

Immunization Safety Office 

CDC 

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Guiding principles for development of ACIP recommendations for vaccination during breastfeeding and pregnancy 

Sandra Steiner, Ph.D. 

Immunology and Methods Development 

Laboratory 

Immunology Section 

Meningitis and Vaccine-Preventable Diseases

Branch 

Division of Bacterial Diseases 

CDC 

Susan A. Wang, MD, MPH 

Division of Viral Hepatitis 

National Center for HIV/AIDS, Viral 

Hepatitis, STD, and TB Prevention 

CDC 

 

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This document can be found on the CDC website at: 

http://www.cdc.gov/vaccines/recs/acip/downloads/preg-principles05-01-08.pdf