Understanding COVID-19 Booster Shots

By Amichai Perlman, PhD, PharmD
Medically reviewed checkmarkMedically reviewed
November 10, 2021

Recently, the FDA and CDC have approved and recommended booster doses of the COVID-19 vaccines. This may have come as a surprise to some of us, as we’ve learned to appreciate the protection offered by these vaccines. I’d like to provide a birds-eye view of the data and reasons for these decisions and who should or could consider getting a booster.

Why are boosters needed?

Extensive research has shown that the currently approved COVID-19 vaccines are very effective at reducing the risk of COVID-19 infection, illness, hospitalization, and death. A few months ago, data from Israel, suggested that the levels of antibodies against COVID-19 decline over time, and that this is accompanied by the waning of the vaccine’s efficacy in preventing infection and illness. Israel is a country where most of the population was vaccinated earlier than the US, and that has comprehensive health data enabling the tracking of vaccine efficacy. This data alerted decision-makers in the US that vaccine boosters may be needed. 

Following the publication of this data, analysis of Pfizer’s vaccine trial data suggested a reduction in protection over time, as did analyses done by the Veterans Health Administration and others. This reduction in efficacy has led to increases in “vaccine breakthrough” (occurrence of COVID-19 among vaccinated individuals) among those who have completed their vaccination more than six months ago. While vaccinated individuals still enjoy considerable protection from severe COVID-19, and often experience mild illness, “vaccine breakthrough” can result in severe COVID-19. 

Do boosters work?

Each of the currently approved vaccines has run clinical trials evaluating the safety and efficacy of booster doses. These trials have found that the boosters safely and effectively increase the levels of antibodies to that which will be effective in preventing COVID-19. This strategy has also been used on a national level in Israel, using Pfizer’s vaccine, and has resulted in a significant decrease in COVID-19 cases, hospitalization, and death. 

Who needs a booster?

Boosters are available for each of the approved COVID-19 vaccines, however, the recommendations regarding their use are somewhat different. 

The CDC recommends that all adults who have received the J&J/Janssen vaccine, which is given as a single dose, should get a booster if at least 2 months have passed since they were vaccinated.

Guidance for people who were fully vaccinated with mRNA vaccines – i.e. Pfizer or Moderna – is more complex. These vaccines are given initially in two doses, have shown very high levels of efficacy in preventing infection in the initial months, and continue to have significant efficacy against severe disease. Nevertheless, due to waning, a third dose is endorsed for many people if at least 6 months have already passed from initial vaccination and they have a higher risk of COVID-19. The considerations governing the recommendations for booster doses of these vaccines include: age, underlying medical conditions, and working or living in settings with high levels of exposure and interactions with people (such as education, grocery stores, etc.). For more specific guidance see the CDC recommendations or consult your healthcare provider.

Importantly, the guidance around boosters is expected to evolve as data regarding vaccine waning and the benefits of boosters accumulates—stay tuned for updates as boosters may soon be recommended even more widely.

K Health articles are all written and reviewed by MDs, PhDs, NPs, or PharmDs and are for informational purposes only. This information does not constitute and should not be relied on for professional medical advice. Always talk to your doctor about the risks and benefits of any treatment.

Amichai Perlman, PhD, PharmD

Dr. Perlman is a clinical pharmacist and pharmacoepidemiologist, with over 10 years of experience advising patients and clinicians on medication use, personalization, and safety. He has extensively published peer-reviewed research addressing medication safety.