Pfizer COVID Vaccine Boosters: Who Needs Them? Who Can Get Them?

Sandra Adamson Fryhofer, MD


October 15, 2021

This transcript has been edited for clarity.

This is part 2 of a Medicine Matters series on "Battle for Boosters." This segment addresses Pfizer/BioNTech mRNA COVID vaccine boosters: Who needs them, and when? (Part 1 of this series, on third vaccine doses for the immunocompromised, can be found here.)

Delta Is Dominant

The Delta coronavirus variant now makes up more than 99% of new COVID cases. Delta is twice as contagious as previous variants. On August 12, 2021, the US Food and Drug Administration (FDA) authorized an additional vaccine dose for certain immunocompromised people when data showed that the regular primary series was not sufficiently protective. This is an additional ("third") dose, not a booster. A booster is given when protection begins to wane over time. Vaccine effectiveness (VE) has decreased over the past 1-2 months. VE pre-Delta was high (about 87%). As Delta became dominant, VE dropped to 39%-84%.

Pfizer Full Approval: Age 16 Years or Older

On August 16, 2021, Pfizer requested full approval of a third dose booster for everyone aged 16 years or older. Data supporting this request were submitted to the FDA. Meanwhile, the Pfizer vaccine two-dose series received full FDA approval for those aged 16 years or older on August 23, 2021. Authorization for a booster was still under FDA review.

Myocarditis Risk

There is risk for myocarditis after the mRNA COVID vaccines. Myocarditis can also occur with COVID infection. Studies now show that myocarditis with COVID infection occurs at higher rates than after mRNA vaccination.

In its review of Pfizer's biologics license application, FDA took a rigorous look at myocarditis risk. They concluded that myocarditis risk is increased after Pfizer mRNA vaccination, particularly within 7 days after the second dose. The risk is higher in males younger than 40 years and highest in young males aged 12-17 years. Some of these patients required hospitalization, and some required intensive care unit admission. Follow-up to date of these patients seems to show resolution of symptoms. The Advisory Committee on Immunization Practices (ACIP) determined that the benefits of a two-dose series clearly outweigh this risk.

Biden Administration Announcement

On August 18, 2021, the Biden administration announced booster shots for everyone to begin the week of September 20, 2021. The initial announcement gave the appearance of getting ahead of FDA and ACIP recommendations. Two top FDA officials announced early retirement and also helped co-author a paper about boosters in the Lancet. The authors concluded that current evidence shows that fully vaccinated individuals remain highly protected against severe COVID disease. Therefore, COVID boosters are not yet needed for the general public. Additional doses would be better used in people who remain unvaccinated.

What the Data Show

On the morning of September 17, 2021, the Centers for Disease Control and Prevention (CDC) released a new study published in MMWR. All three authorized and approved COVID vaccines show substantial protection from COVID-related hospitalization. Moderna had the highest VE at 93% compared with the Pfizer (VE = 88%) and Janssen vaccines (VE = 71%). However, Pfizer vaccine effectiveness declined significantly from 91% down to 77% at more than 4 months after the second vaccine dose.

The FDA's Vaccines and Related Biological Products Advisory Committee (VBRPAC), an independent advisory committee, met later that day to review Pfizer's booster request for those aged 16 years or older. At that meeting, Pfizer presented data showing waning vaccine immunity at 6-8 months after the second vaccine dose. They extrapolated data from 300 people aged 18-55 years to both younger (aged 16-17 years) and older individuals.

Israeli officials shared data on how they were dealing with Delta in the COVID pandemic. Their third-dose booster program showed more than a 10-fold improved protection against confirmed infection and severe COVID. Month-long data in patients aged 60 years or older had been published in the New England Journal of Medicine. Israel's data revealed only one case of myocarditis (so far) out of 2.8 million people who received a third dose. However, the youngest people who had received a third dose, those aged 16-29 years, only had about 2 weeks of follow-up.

The FDA advisory panel expressed the need for more long-term safety data, particularly if the booster will be given to young people.

The essence of the discussion was whether boosters should be given at a time when vaccines are still offering high protection against severe disease. The value of giving boosters at this time would be the hope of blocking milder breakthrough infections among those who are fully vaccinated.

The CDC concluded that the vaccines continue to maintain high protection against severe disease, hospitalization, and death.

Booster Decisions

Pfizer's request for a third-dose booster for everyone aged 16 years or older was soundly defeated by the VBRPAC. Boosters for those aged 65 years or older and for those at high risk for severe COVID received unanimous support. Boosters for healthcare workers and others at high risk for occupational exposure, including teachers, were also supported.

Because VBRPAC is an independent advisory committee, their recommendations are not binding, but FDA's final decision was in line with the advisory committee's recommendations. FDA authorized emergency use of a single Pfizer booster dose, at least 6 months after a primary series for those aged 65 years or older, for those aged 18-64 years who are at high risk for severe COVID, and for those aged 18-64 years whose "frequent institutional or occupational exposure to COVID" puts them at high risk for serious complications of COVID, including severe COVID and the risk for long-haul COVID.

In its news release, FDA explained this would allow booster doses for healthcare workers, teachers, day care staff, grocery workers, and those in homeless shelters and prisons.

ACIP met on September 22 and 23, 2021, reviewed these data, and weighed in. ACIP voted unanimously in favor of a Pfizer booster, at least 6 months after a primary Pfizer series, for adults aged 65 years or older, as well as for residents of long-term care facilities of any age. ACIP gave a thumbs-up for booster doses for persons 50-64 years of age with underlying health conditions. ACIP also voted in favor of boosters for 18- to 49-year-olds with underlying medical conditions, on the basis of individual benefit and risk. ACIP voted "no" for boosters for those aged 18-64 years in an occupational or institutional setting where the burden of COVID infection and risk for transmission are high. Understand that this meant no boosters for healthcare personnel. This was a reversal of FDA's emergency authorization.

ACIP recommendations have to be approved by the CDC director; that's standard procedure. Dr Rochelle Walensky, CDC Director, overruled ACIP's final vote, thus allowing boosters for those at occupational risk. This makes booster shots available to healthcare personnel, teachers, and others who risk contracting COVID on the job.

The definition of "fully vaccinated" has not changed. For public health purposes, it is still 2 weeks after two mRNA doses or a single Janssen dose. Even with all this talk about boosters, the top priority is still to vaccinate those not yet vaccinated.

In summary, Pfizer boosters only apply to adults who received a Pfizer series. In a nutshell, you must be aged 65 years or older, or have health issues, or a high exposure job or conditions, to qualify. This recommendation is only for Pfizer boosters. There are no boosters yet for Moderna vaccine; there is a recommendation for additional Moderna doses for immunocompromised persons. There is still no additional guidance for boosters or additional doses after a single Janssen vaccine dose. Moderna has submitted their booster data to FDA. On October 14 and 15, 2021, VBRBAC, FDA's independent advisory committee, will look at data submitted by Moderna and Janssen requesting authorization for booster doses.

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