Second COVID-19 booster: who can get one, and when?

Following much debate among public health experts about the benefits of another COVID-19 booster, the U.S. Food and Drug Administration could approve second boosters of the mRNA vaccines as an option for people 50 and older this week, according to multiple media reports. Currently, just one booster is recommended by the Centers for Disease Control and Prevention.

We asked Michael Lin, MD, MPH, an infectious disease specialist and associate professor at Rush University Medical Center, to offer his insights on the booster debate.

Why don’t all experts agree on whether we need another COVID-19 booster?

One issue driving the recent controversy over boosters is that not all public health officials have the same goals regarding vaccination, Lin says.

Most would agree that the primary goal of the vaccines is to keep people from developing severe COVID-19 that could lead to hospitalization or death, Lin says. Based on that metric, the vaccines seem to be maintaining their effectiveness for most people. Data shows the Pfizer-BioNTech and Moderna vaccines appear to be 78% effective at preventing hospitalization from COVID-19 four months after a third dose.

Yet some public health experts also believe that another goal of the vaccines is to prevent any infection with SARS-CoV-2 (the virus that causes COVID-19) in the hopes of slowing down—or even stopping—transmission in the community. On that front, the vaccines have been less effective. “We have seen waning immunity to any infection, including mild infection, especially this past winter when the delta wave ended and the omicron wave began,” Lin says. “That is why many people are recommending another booster.”

Lin says experts on both sides of the argument have valid points. “They just have different priorities,” he adds. He did not want to speculate on the FDA’s actions this week but expects the government will balance the risks and benefits before giving certain vulnerable population groups the option to get a second booster.

When would be the best time to get another booster?

Some public health officials want to get the option of a second booster for those 50 and older authorized ahead of another potential surge, especially as the BA.2 omicron subvariant continues to spread.

“With the omicron wave, it appeared that the effectiveness of the booster at preventing infection was most apparent in the one to two months after the booster was given. After that, the effectiveness started to wane, at least for the omicron variant,” Lin says. “So, it makes sense to push for boosters at the beginning of a wave, rather than at the end of a wave when there are low rates of transmission in the community.”

When will we know if we can get another COVID-19 booster?

Even though reports suggest that the FDA could authorize a second booster this week, the agency has also scheduled a meeting for April 6 to discuss the government’s overall COVID-19 vaccine and booster strategy.

Although the FDA controls approval of vaccines and boosters, it is the CDC’s Advisory Committee on Immunization Practices that usually recommends which populations should get boosted and when. “That’s another set of hoops that need to be jumped through before there might be a recommendation on another booster,” Lin says. So, it could be a few weeks before people 50 and older have the option to get another booster.

Who is eligible for a fourth dose of an mRNA vaccine now?

“As it stands, the most common reason to get a fourth dose is if you are immunocompromised,” Lin says.

Currently, the CDC recommends that people ages 12 and older with weakened immune systems receive three full doses of an mRNA vaccine as part of their primary series. The CDC also advises people in this group to get a booster, for a total of four shots. “That advice reflects the idea that immunocompromised people have a harder time making protective antibodies,” he says.

Will yearly COVID-19 boosters be needed?

Lin thinks it’s possible that yearly boosters could be recommended at some point to protect against COVID-19. As epidemiologists at RUSH and elsewhere collect more infection data in the coming months, public health officials will have more information on which to base their recommendations for the next cold and flu season.

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