For more information: www.cdc.gov/COVID19

Implementation considerations 

for COVID-19 Vaccines

ACIP COVID-19 Vaccines Work Group

Dr. Kathleen Dooling, MD, MPH

ACIP Emergency Meeting, March 1, 2021
Outline- Implementation Considerations

▪ Janssen COVID-19 vaccine

▪ COVID-19 vaccine prioritization

▪ Dosing intervals for mRNA vaccines
Janssen COVID-19 vaccine

▪ ACIP states no preference for any of the three authorized vaccines

▪ Results of Janssen Phase III trials not comparable with mRNA vaccines

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Different calendar time

Different geography

▪ Strong protection against severe COVID-19

93% VE against hospitalizations (2 cases in vaccinated vs. 29 in placebo)

No COVID-associated deaths in vaccinated vs. 7 in placebo

Different circulating variants

Higher background incidence
Janssen COVID-19 Vaccine

How does it best fit?

Characteristics of the vaccine

▪ 1 dose

▪ Transport, and storage (x3m) at 2-8

oC

▪ No diluent/reconstitution necessary
Janssen COVID-19 Vaccine:

Considerations for utilization 

Where?

▪ Mobile/pop-up clinics

▪ Newly established vaccine 

administration sites 

▪ Sites that do not have freezer 

capacity (e.g. adult HCP 

offices)

Who?

▪ People who want to be fully 

vaccinated quickly

▪ People who don’t want to 

return or can’t return for a 

second dose

▪ Mobile populations or 

homebound populations
COVID-19 Vaccine Work Group considerations

▪ During a pandemic, under EUA, offering Janssen COVID-19 vaccine to 

persons 18 years and older, according to established allocation and 

eligibility recommendations in a given jurisdiction, is an effective 

implementation strategy

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Allows for jurisdictional flexibility

Supports rapid vaccination and increases in population immunity

Does not single out any group

Allows individuals to be vaccinated with the earliest vaccine available
COVID-19 vaccine prioritization
▪ Ensure safety and effectiveness of COVID-19 vaccines

▪ Reduce transmission, morbidity, mortality of COVID-19 disease

▪ Help minimize disruption to society and the economy, including maintaining 

healthcare capacity

▪ Ensure equity in vaccine allocation and distribution

Work Group Considerations: 

Goals of the COVID-19 Vaccine Program
COVID-19 Vaccination Program: Ongoing Roll-Out

Current status

▪ >72M doses administered, as of February 27

▪ Continued constrained COVID-19 vaccine supply

▪ Continued reliance on large vaccination centers

▪ Most jurisdictions are in Phase 1b or expanding 

into Phase 1c

▪ Most states have made modifications to the ACIP 

prioritization framework1

• Sub-prioritization or delay of essential workers

• Adding age bands <65 years

• Sub-prioritization of high-risk medical 

conditions or requiring ≥2 conditions 

Estimated doses by the 

end of March 20212

▪ Pfizer: 120M doses 

(>37M administered)

▪ Moderna: 100M doses 

(>35M already administered)

▪ Janssen: 20M doses

1. https://energycommerce.house.gov/committee-activity/hearings/hearing-on-pathway-to-protection-expanding-availability-of-covid-19

2. https://www.kff.org/other/state-indicator/state-covid-19-vaccine-priority populations
Implementation Challenges and Considerations

▪ Challenge: difficulty adjudicating eligibility in large vaccination centers

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E.g. Essential worker & High-risk conditions

Verification of eligibility should not hamper throughput at large 

vaccination clinics

Medical care homes/Primary Care Providers may be better able to assess 

eligibility on the basis of underlying medical conditions

▪ Challenge: implementing the list of high-risk conditions

CDC list relies on published studies and is not exhaustive

Certain conditions on the list encompass a wide range of severity

Clinical judgement may determine if rare conditions not on the list confer 

increased risk of severe COVID-19.
Implementation Challenges and Considerations

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Challenge: size of eligible groups in Phase 1c may exceed vaccine supply

Consider addition of an eligibility age bands <65 yrs (e.g. 60-64 or 55-64 or 50-64)

Consider prioritizing persons with ≥2 high-risk conditions

Challenge: transmission in congregate settings (eg prisons, homeless shelter or LTCF)

Consider offering vaccine to all unvaccinated staff and residents at the same time
Implementation Challenges and Considerations

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Challenge: promoting heath equity while ensuring efficient vaccine distribution and 

administration

Use Social Vulnerability Index (SVI) or other needs-based index to place vaccine 

clinics

Partner with Federally Qualified Health Centers (FQHCs) to be vaccination hubs and 

help register eligible community members for vaccination

Offer Janssen COVID-19 vaccine as an option for populations for whom returning for 

a second dose would be difficult

Community engagement and education will be important as new COVID-19 vaccines 

are authorized and recommended for use
Dosing intervals for mRNA vaccines
Dosing intervals for mRNA vaccines

Two issues:

1. Delay the second dose?

2. Single dose of mRNA vaccine for individuals with confirmed prior 

SARS-coV-2 infection?
Issue # 1: 

Delay the second dose?

▪ Background: Extended inter-dose intervals have been adopted by other national 

vaccine advisory groups and proposed by individuals in the U.S. as a strategy to increase 1-

dose coverage during a time when demand exceeds supply

▪ Current guidance: "The second dose should be administered as close to the 

recommended interval as possible. However, if it is not feasible to adhere to the 

recommended interval, the second dose of Pfizer-BioNTech and Moderna COVID-19 

vaccines may be scheduled for administration up to 6 weeks (42 days) after the first 

dose."

https://www.cdc.gov/vaccines/covid-19/info-by-product/clinical-considerations.html
Issue # 1: 

Delay the second dose?

▪ Phase I/II clinical trials: Neutralizing antibodies did not show large increases until after receipt of 

the 2nd dose (both Pfizer and Moderna).

▪ Phase III trials: 97-98% of recipients received both doses. Only studied out to 3 weeks 

(Pfizer) or 4 weeks (Moderna). VE estimated at 50-90% (higher when starting 2 weeks after 1st 

dose).

▪ “Real world” effectiveness:

74%

78%

60%

72%

85%

68%

64%

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

14-20 21-27 14-20 21-17 28-34 35-41 ≥42

Effectiveness against COVID-19 

associated hospitalization

Days post-dose 1, Pfizer COVID-19 vaccine 

 

Recent studies evaluating effectiveness of Israel Scotland

1-dose of Pfizer vaccine to prevent COVID-19 

associated hospitalizations: 

Matched case control study, Israel1: 

VE increased to 78% 21-27 days post-dose 1

Prospective cohort study, Scotland2: 

VE increased to 85% 28-34 days post-dose 1, 

__but then declined

1Dagan N, et al. NEJM, 2021; 2Vasileiou E, et al. Lancet, preprint 2021
Issue #1: 

Delay the second dose?

Pros Cons

Could provide 1 dose protection to a larger 

number of people over the next several 

months. If 1 dose protection is high and 

persists, this could prevent more infections 

and deaths1.

Lower neutralization antibodies could be protective against 

‘wild-type’ COVID-19, but not novel variants2-4. 1-dose 

vaccination could leave individuals susceptible to variants, 

providing selective pressure and increase transmission of 

variants5.

Boosting still likely to be effective, even at 

longer interval

Estimates of effect for a single dose are imprecise and duration 

of protection after the 1st dose is unknown.

Would contradict FDA’s Emergency Use Authorization

(2-dose series, 3 or 4 weeks apart)

1Accelerate COVID-19 Vaccine Rollout by Delaying the Second Dose of mRNA Vaccines https://doi.org/10.1093/cid/ciab068

1The effectiveness of the first dose of BNT162b2 vaccine in reducing SARS-CoV-2 infection 13-24 days after immunization: real-world evidence | medRxiv

2

Increased resistance of SARS-CoV-2 variants B.1.351 and B.1.1.7 to antibody neutralization. 2021.01.25.428137v2.full.pdf (biorxiv.org)

3SARS-CoV-2 variant B.1.17 is susceptible to neutralizing antibodies elicited by ancestral Spike vaccines Microsoft Word - Shen_B117_ver10.docx (biorxiv.org)

4The E484K mutation in the SARS-CoV-2 spike protein reduces but does not abolish neutralizing activity of human convalescent and post-vaccination sera | medRxiv

5Epidemiological and evolutionary considerations of SARS-CoV-2 vaccine dosing regimes https://doi.org/10.1101/2021.02.01.21250944;
Issue # 1: 

Delay the second dose?

https://www.cdc.gov/vaccines/covid-19/info-by-product/clinical-considerations.html

▪ Summary of Work Group Discussions:

▪ Currently, there are insufficient data to increase recommended intervals

▪ Important uncertainty regarding protection from the variants following 1 dose 

of mRNA COVID-19 vaccines

▪ Next Steps:

▪ Continue to monitor post-authorization effectiveness studies

▪ Any updates to vaccine recommendations will be:

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Evidence based

Discussed publicly

Made in collaboration with FDA
Issue # 2: 

Single dose of mRNA vaccine for individuals with confirmed prior 

SARS-CoV-2 infection?

https://www.cdc.gov/vaccines/covid-19/info-by-product/clinical-considerations.html

▪ Background: There have been anecdotal reports of increased reactogenicity following

vaccination among people with prior COVID-19. Additionally, recently published reports 

suggest high antibody response after 1 dose for individuals with prior SARS-CoV-2 

infection

▪ Current guidance: "...while vaccine supply remains limited, persons with recent 

documented acute SARS-CoV-2 infection may choose to temporarily delay vaccination, if 

desired, recognizing that the risk of reinfection, and therefore the need for vaccination, 

might increase with time following initial infection."
1Robust spike antibody responses and increased reactogenicity in seropositive individuals after a single dose of SARS-CoV-2 mRNA vaccine | medRxiv

2Single Dose Vaccination in Healthcare Workers Previously Infected with SARS-CoV-2 | medRxiv

Immunogenicity evaluated in 2 pre-print studies1,2: 

Assessed antibody titers after 1 dose in seropositive compared to seronegative individuals

Both studies showed higher antibody titers in seropositive individuals after 1 dose

Issue # 2: 

Single dose of mRNA vaccine for individuals with confirmed prior 

SARS-CoV-2 infection?
1Robust spike antibody responses and increased reactogenicity in seropositive individuals after a single dose of SARS-CoV-2 mRNA vaccine | medRxiv

Reactogenicity evaluated in 1 preprint study1: 

▪ Localized injection site symptoms occurred 

with similar frequency.

▪ Systemic side effects occurred at higher 

frequency among individuals with preexisting immunity: 

– Similar to symptoms reported for the second 

dose in the Phase 3 trials

Issue # 2: 

Single dose of mRNA vaccine for individuals with confirmed prior 

SARS-CoV-2 infection?
Pros Cons

Could ‘free up’ 2nd doses for 

seropositive persons to be provided to 

seronegative persons

Current studies included individuals with confirmed antibodies 

to SARS-CoV-2. Performing large-scale antibody screening prior 

to vaccination is not feasible

Seropositive persons would not receive 

2 doses of reactogenic vaccine

Correlate of protection currently unknown; unable to 

extrapolate antibody studies to vaccine effectiveness

Limited data (small studies) currently

Would contradict FDA Emergency Use Authorization

(2-dose series, 3 or 4 weeks apart)

Issue # 2:

Single dose of mRNA vaccine for individuals with confirmed prior 

SARS-CoV-2 infection?
Issue # 2: 

Single dose of mRNA vaccine for individuals with confirmed prior 

SARS-CoV-2 infection?

▪ Summary of Work Group Discussions:

▪ Currently there are insufficient data to support changes to guidance or recommendations

▪ This is an area to pursue further data 

▪ Consider promotion of existing guidance: those with prior infection may choose to temporarily delay 

vaccination for several months

▪ Next Steps:

▪ Collect and review further data on safety and reactogenicity as well as immunogenicity and effectiveness of 

COVID-19 vaccines among individuals with prior infection

▪ Any updates to vaccine recommendations will be:

– Evidence based

– Discussed publicly

– Made in collaboration with FDA
Janssen COVID-19 vaccine

▪ Do you agree that offering Janssen COVID-19 vaccine to persons 18 years and older, according to 

established allocation and eligibility recommendations, is an effective implementation strategy?

Vaccination Prioritization

▪ What are the key challenges and opportunities of implementation guidance options for

1. Additional age eligibility brackets <65 years

2. Elegibility based on 2 or more high risk condition

mRNA vaccine dosing

▪ What additional data is needed to inform

1. Delay the second dose?

2. Single dose of mRNA vaccine for individuals with confirmed prior SARS-coV-2 infection?

Questions for ACIP
Janssen COVID-19 vaccine

▪ Do you agree that offering Janssen COVID-19 vaccine to persons 18 years and older, 

according to established allocation and eligibility recommendations, is an effective 

implementation strategy?

Questions for ACIP
Vaccination Prioritization

▪ What are the key challenges and opportinities of implementation guidance options for

1. Additional age eligibility brackets <65 yrs

2. Elegibility based on 2 or more high risk condition

Questions for ACIP
mRNA vaccine dosing

▪ What additional data is needed to inform

1. Delay the second dose?

2. Single dose of mRNA vaccine for individuals with confirmed prior 

SARS-coV-2 infection?

Questions for ACIP
For more information, contact CDC

1-800-CDC-INFO (232-4636)

TTY: 1-888-232-6348 www.cdc.gov

The findings and conclusions in this report are those of the authors and do not necessarily represent the 

official position of the Centers for Disease Control and Prevention.

Thank you