by Robert H. Shmerling, MD: Vaccination against the virus that causes COVID-19 is the most important lifesaving tool we have in this pandemic…


Fortunately, the vaccines authorized in the US have proven remarkably safe and effective. And we’ve known from the start that the strong protection they provide would likely wane over time.

But has protection declined enough to warrant booster shots? Studies published in the last few months by researchers in the UK, Israel, and the US (reviewed here and here) raised this possibility, and Israel and the UK have already started ambitious booster programs.

First things first: Vaccinate everyone

As you probably know, the CDC and FDA have reviewed the necessity, safety, and effectiveness of boosters for the Pfizer/BioNTech vaccine. So far that’s the only booster shot being offered, although both agencies will review data for Moderna and Johnson & Johnson in the weeks and months to come. (I’ll discuss Pfizer recommendations in a moment.)

But first, it’s important not to overlook this fact: vaccinating the unvaccinated should be a much bigger priority than giving booster shots to those who’ve received vaccines. That goes for people in the US who have been unable or unwilling to get the vaccine, and people in places throughout the world with limited access to vaccines.

Broadening the pool of people with initial vaccinations would not only save more lives than promoting boosters, but would also reduce COVID-related healthcare disparities between richer and poorer countries. That’s why the World Health Organization (WHO) called for a moratorium on booster doses. Meanwhile, the Biden administration has announced a promise to donate another half billion vaccines to countries with low vaccination rates, bringing the total US commitment to donate 1.1 billion doses. The administration emphasizes that starting a booster program in the US and helping other countries get their citizens vaccinated are not mutually exclusive.

Is there a difference between a booster dose and a third shot?

It’s not trick wording: not all extra vaccine doses are boosters. In August 2021, the FDA approved a third dose of the Pfizer or Moderna vaccine for people who are immunocompromised. This includes people who have HIV and those receiving treatment for cancer that suppresses the immune system. For them, the extra dose is not a booster; it’s considered part of their initial immunization series.

Getting the timing right on vaccine boosters

Ideally, vaccine boosters are given no sooner than necessary, but well before widespread protective immunity declines. The risks of waiting too long are obvious: as immunity wanes, the rates of infection, serious illness, and death may begin to rise.

But there are downsides to providing boosters too early:

  • Side effects might be more common. While studies published to date suggest that boosters are safe, we don’t yet have long-term data.
  • The benefit may be small. It may be better to wait on boosters if most people are still well-protected by their initial vaccinations.
  • Current boosters may not cover future variants. If new variants of concern emerge in the coming months, boosters may be modified to cover them.
  • Waiting longer before a booster might lead to a stronger immune response. As noted by Dr. Anthony Fauci recently: “If you allow the immune response to mature over a period of a few months, you get much more of a bang out of the shot.”

Recommendations for Pfizer/BioNTech vaccine boosters

For some recipients of the Pfizer/BioNTech vaccine, the CDC and FDA have concluded that the time for boosters is now. A booster is recommended at least six months after the second dose for those who are

  • 65 or older
  • 18 to 64 and at high risk for severe illness from COVID, such as people with chronic lung disease, cancer, or diabetes
  • living or working in a high-exposure setting, such as residents of long-term care facilities, healthcare workers, teachers and day care staff, grocery workers, and prisoners.

No Pfizer/BioNTech boosters are recommended for the general population yet. That’s because the initial doses still appear to be providing good protection against severe illness and death.

Plenty of unknowns

The release of these new recommendations for Pfizer vaccine boosters raises a number of questions:

  • How convincing is the safety data? Reports to date suggest boosters are safe, but we need more research and real-world data.
  • How soon will decisions be made regarding the authorization of Moderna and Johnson & Johnson boosters?
  • Should all boosters be the same vaccine as the initial regimen, or does mixing vaccines offer broader protection? Unfortunately, some people are mixing vaccines on their own — sometimes by falsely claiming not to have had a COVID vaccine in order to get a different type. But there’s no solid evidence assessing the risks or benefits of this approach.
  • Will the dose of boosters be the same as the initial doses? So far, the answer is yes for the Pfizer/BioNTech vaccine. But the Moderna booster, once authorized, will likely be for a half-dose.
  • Will the boosters be modified to protect against emerging variants of concern?
  • Will additional boosters be needed in the future? If so, how often?

Look for answers to these questions in the coming weeks and months.

What’s next?

You can expect the FDA and CDC to revise and expand booster recommendations based on continued review and analysis of ongoing research. In the meantime, we should redouble our efforts to vaccinate people who haven’t yet received vaccines. Boosters can play an important role in protecting individuals. But, as CDC director Dr. Rochelle Wallensky notes, “we will not boost our way out of this pandemic.”

Source: Harvard