You Likely Don’t Need a Fourth Covid Shot

Unless you’re at high risk, the initial two vaccine doses are enough

By Philip Krause and Luciana Borio.

"How many Covid shots are enough? Pfizer and Moderna have asked the Food and Drug administration to authorize a second booster (a fourth shot) for patients over 65 and all adults, respectively. The FDA reportedly will authorize (but not recommend) the fourth shot for patients over 50. But if your immune system is healthy, three or even two doses of these mRNA vaccines should be sufficient.

Vaccine-induced protection against infection is short-lived and doesn’t get much of a boost from extra shots. Yet the initial two-dose regimen is enough to provide most patients excellent protection against severe disease—mediated by durable cellular responses, not the neutralizing antibodies that rise and wane quickly after vaccination.

The New York State Health Department’s large database shows the effectiveness of full vaccination (that is, at least two mRNA doses) remained above 90% against hospitalization, including during the recent Omicron surge. A study from Sweden found the same. Studies from Qatar and California showed no decline in protection against severe disease with Omicron.

Booster advocates point to other studies that show declining vaccine effectiveness over time, especially against Omicron. But these appear unreliable, reporting a range of results for vaccine efficacy against symptomatic disease from as high as 40% to 50% to as low as negative 40%.

When assessing vaccine efficacy, scientists compare the rate of disease between vaccinated and unvaccinated groups; a larger difference indicates higher vaccine efficacy. But as more unvaccinated people become immune through infection—especially with a highly transmissible variant—the gap between the groups narrows even if the vaccines are still effective.

What about studies that report reduced rates of Omicron hospitalization in the boosted vs. the unboosted? The variant’s reduced virulence means that a much smaller percentage of vaccinated people end up in the hospital. Those who do are likelier to have serious underlying health conditions. Boosting this population helps. But for immunocompetent people with one or no risk factor, two doses remain 95% effective in preventing severe Covid.

Evidence for a fourth dose is even less compelling. The largest Israeli study reported that fewer than 1 in 200 people over 60 who got Omicron ended up with severe disease after three doses. A fourth dose further reduced that likelihood, but the effect was driven by those with major risk factors. There’s no evidence that introducing boosters last fall had a significant impact on the course of the Omicron surge in the U.S.

If you’ve had two doses of vaccine, you have a lot of protection against severe Covid. Likewise if you’ve been infected with the virus, including with Omicron. If you’re over 65 or otherwise at high risk of severe disease, it’s reasonable to get a third dose. A fourth dose is already authorized for the immunocompromised. For everyone else, the data haven’t shown meaningful benefit of three doses, never mind four.

Dr. Krause is a consultant to the World Health Organization and was deputy director of FDA’s Office of Vaccines Research and Review, 2011-21. Dr. Borio is a senior fellow for global health at the Council on Foreign Relations and was director for medical and biodefense preparedness policy at the National Security Council, 2017-19."