COVID Booster Shot: Moderna or Pfizer?

Should You Choose Pfizer or Moderna for a COVID-19 Booster Shot? As your doctor will likely advise you, the best booster shot is the one available to you now, so we encourage all our clients and readers who are eligible for a booster shot to get one and not delay. That's especially true given the high transmissibility of Omicron. While we aren't particularly worried about Omicron per se, now that we've been boosted, we are very concerned about the effect of the Omicron wave on hospital resources across the U.S. and in many other countries. Even though Omicron typically results in mild cold-like symptoms when it infects vaccinated people, the sheer numbers of people being infected during the current surge means that more people, including vulnerable and immune compromised patients, are requiring hospitalization. That impacts people needing non-covid care as well, and of course the morale of doctors, nurses, and healthcare workers.

Nevertheless, if you are fortunate enough to have a choice of booster shots, we recommend a Moderna shot, even if you previously were vaccinated with Pfizer or J&J. Not only does it have more micrograms of mRNA in it (the original Moderna dose has 100 micrograms vs. 30 micrograms in the Pfizer dose, so even the Moderna booster, which is half of a regular vaccine dose, has 50 micrograms vs. 30 micrograms in the Pfizer booster, which is the same size as the original), there is now more evidence of the stronger capabilities of Moderna to neutralize Omicron via a recent study mRNA-based COVID-19 Vaccine Boosters Induce Neutralizing Immunity Against SARS-CoV-2 Omicron Variant published in Cell.

In the study, blood samples were taken from participants who were in one of four groups: 1) Recently vaccinated (within the past 3 months) with Pfizer, Moderna or J&J; 2) Vaccinated 6-12 months ago; 3) Vaccinated 6-12 months ago and also had been infected by COVID-19; and 4) Received a full vaccine series plus booster shot.

As seen above, group 2, those vaccinated 6-12 months ago, fared worst of all (except for Pfizer, where interestingly those recently vaccinated with two Pfizer vaccine shots within the past 3 months were even less able to generate antibodies to neutralize Omicron than those vaccinated 6-12 months ago). Recently vaccinated people were the next worse off, although in this group it was far better to have been vaccinated with Moderna's two shots than with Pfizer's, and also better than with J&J's one shot vaccine. In group 3, those who were fully vaccinated 6-12 months ago but had also at one point been infected with COVID-19, the worst off were those vaccinated with J&J, next was Pfizer, and Moderna recipients remained the most protected.

With Omicron, Moderna and Pfizer showed similar antibody neutralizing capabilities, and three doses of either outperformed J&J plus a Moderna booster (none of the study's J&J vaccine recipients chose Pfizer as a booster). But when looking at the few participants who switched vaccines from their original series, it's interesting to note that two of the original Pfizer vaccine recipients who received a Moderna booster showed the second and third highest protection among Pfizer vaccine recipients who were boosted, while among original Moderna vaccine recipients, the only study participant who chose a Pfizer booster instead of a Moderna booster fared worse than at least 7 others who were entirely vaccinated, including the booster, with Moderna. While this was a relatively small sample size of 239 individuals, it would be interesting to see if these results are confirmed by other studies.

Keep in mind as well that this study focused on neutralizing antibodies, which doesn't encompass the body's other protective defenses, such as T cells.

The potential downsides of the Moderna booster: 1) it's not available to those under 18 years old, so kids 12-17 aren't eligible; and 2) the greater amount of mRNA can mean stronger side effects for some. Personally, I felt pretty rotten for 24 hours after both the second dose and booster dose, although that's a small price to pay for improved protection.

The upshot:

Don't procrastinate on getting a booster shot. If you think your antibody response against Omicron from two doses of Pfizer or Moderna or one shot of J&J is similar to what it will be if you get a booster, think again.
If you're recently vaccinated, your antibody response isn't as strong as someone vaccinated 6+ months ago who also got a booster.
If you only got one shot of J&J, get a Moderna or Pfizer booster (preferably Moderna). Even so, your antibody response post-booster isn't likely to be as strong as if you had received two doses plus a booster of Pfizer or Moderna
If you received two doses of Pfizer, either a Pfizer or Moderna booster is great, but Moderna appears to have the edge over Pfizer.

Separately, Singapore recently released some data of the 802 people who died of COVID-19 in 2021 in Singapore. Because of the timing, this speaks more to Delta and vaccines, not Omicron, which only appeared in Singapore on 12/9/21. 70% of those who died weren't fully vaccinated. Of those who were vaccinated, those vaccinated with Moderna fared best: 1 per 100K, vs. 6.2 per 100K for Pfizer, 7.8 for Sinopharm and 11 for Sinovac. That said, this was a small sample size and other factors such as age, health, and timing of the doses affect mortality.

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