Five Things to Know about COVID-19 Vaccine Booster Shots


Dr. Todd Ellerin

Todd Ellerin, MD, Director of Infectious Disease

A photo of several vials of COVID-19 vaccine

COVID-19 booster shots are here, but not everyone will be eligible for a third dose initially.

The Food and Drug Administration (FDA) this week authorized Pfizer-BioNTech’s COVID-19 booster shots for people over the age of 65 and other vulnerable Americans six months after they complete their second dose of the vaccine.

The Centers for Disease Control and Prevention’s (CDC) Advisory Committee on Immunization Practices (ACIP) followed the FDA’s decision with new recommendations of its own on September 24, issuing updated guidance to allow millions of Americans at highest risk for COVID-19 to receive a booster shot of the Pfizer-BioNTech vaccine.

Debate continues among the scientific community and within the FDA about whether COVID-19 vaccine boosters are yet needed for the general public, ages 16 and up.

Here are five more things to know about COVID-19 booster shots.

Who can roll their sleeves up first for a booster shot? 

The newest CDC guidance features the following recommendations:

  • People 65 years and older and residents in long-term care settings should receive a booster shot of Pfizer-BioNTech’s COVID-19 vaccine at least 6 months after their Pfizer-BioNTech primary series.
  • People aged 50–64 years with underlying medical conditions should receive a booster shot of Pfizer-BioNTech’s COVID-19 vaccine at least 6 months after their Pfizer-BioNTech primary series,
  • People aged 18–49 years with underlying medical conditions may receive a booster shot of Pfizer-BioNTech’s COVID-19 vaccine at least 6 months after their Pfizer-BioNTech primary series, based on their individual benefits and risks, and
  • People aged 18-64 years who are at increased risk for COVID-19 exposure and transmission because of occupational or institutional setting may receive a booster shot of Pfizer-BioNTech’s COVID-19 vaccine at least 6 months after their Pfizer-BioNTech primary series, based on their individual benefits and risks.

Pfizer’s shot the only vaccine booster approved so far

The FDA’s authorization for boosters only applies to the Pfizer-BioNTech COVID-19 vaccine; Moderna submitted the required data on its booster to the agency earlier this month, and data on the Johnson & Johnson/Janssen vaccine booster is expected within a few weeks.

While all three COVID vaccines currently available in the U.S. remain effective in preventing severe disease, the virus is continually evolving.

Medical and public health experts continue to assess available data to understand how well the vaccines are working, including the way in which variants, like Delta, affect their effectiveness.

The difference between ‘third’ doses and vaccine booster shots

While COVID-19 booster shots have not been approved yet for the general public ages 16 and up, last month the FDA and CDC recommended that immunocompromised individuals who have not built sufficient protection against the virus following their initial vaccination get an additional dose of an mRNA COVID-19 vaccine – Pfizer-BioNTech or Moderna – at least 28 days after their second shot.

This third dose can help build more protection against the disease for those who are immunocompromised.

Booster doses are for those who have built enough protection following vaccination, but that protection has decreased over time.

More studies needed to authorize boosters for all

In order to determine whether or not booster shots will be made available to the general public, more data is needed.

The only real data available on the booster so far is in a large Israeli observational study of about a million people 60 years and older, which involved a short-term follow up of 12 days. 

The booster appeared very effective in reducing symptomatic infection over the short term (10-20 fold), compared with the unboosted group.

Boosters for the Johnson & Johnson/Janssen vaccine

According to the CDC, people who received the Johnson & Johnson/Janssen vaccine will also likely need a booster dose.

Studies are ongoing, but a report this week from the pharmaceutical company’s most recent trial showed encouraging results for the J & J/Janssen COVID-19 vaccine booster.  

Because the one-shot vaccine was not administered in the U.S. until March – more than two months after the first mRNA doses of the Pfizer and Moderna vaccines were given – the CDC does not yet have the data necessary to consider authorizing a J&J/Janssen booster. 

Only about 14 million people in the U.S. have received the J&J/Janssen vaccine.

In comparison, 205 million have received the Pfizer vaccine and close to 144 million got the Moderna shot.

CDC data does not support getting a Pfizer or Moderna mRNA vaccine booster if you previously received the J&J/Janssen vaccine.

Increasing overall vaccination rates remains a priority

As the FDA and CDC move closer to authorizing COVID-19 boosters for the general public, we must continue to encourage the millions still unvaccinated to get their shots.

The vast majority of COVID-19 cases resulting in severe illness, hospitalization, or death are now occurring among the unvaccinated.

The best way to stay ahead of the virus and to limit future mutations and variants is the have as many people vaccinated as possible.

While it is understandable that those currently vaccinated would like additional protection, we must work on raising the overall vaccination rate to better protect everyone.

Todd Ellerin, MD is Director of Infectious Disease at South Shore Health.