On January 3, Israel—which had led the global movement to give out third shots—started offering a fourth dose of COVID-19 vaccines to medical workers and people older than 60. Days earlier, it approved an extra booster shot for people with weak immune systems. In the U.S., some people are already trying to get an unauthorized fourth, or even fifth, dose before it’s recommended.
Is the Israeli government right or being overly cautious? If you’re fully vaccinated and boosted, is an extra dose necessary? For most people, probably not. “The endless chasing of boosters in order to increase antibodies and increase marginal relative protection but modest absolute benefit is a waste of resources,” says Naor Bar-Zeev, deputy director of the International Vaccine Access Center at the Johns Hopkins Bloomberg School of Public Health.
A trial in Israel that started on December 27 gave a fourth dose of vaccine to medical workers who had gotten their first booster shot at least four months earlier. The trial participants had low antibody levels, and the fourth dose made antibody levels rise. But “just the antibody level alone isn’t predictive of protection,” Bar-Zeev says. Antibody levels are supposed to fall as the immune system builds up a longer-lasting response. (The trial is so new, of course, that there’s no evidence yet of how much the fourth dose may help in the long term.)
If it’s been months since you got a COVID-19 booster shot, you may be somewhat more likely to get infected with the virus, but you should still have protection against severe disease. That happened with the delta variant, Bar-Zeev says, and it’s likely to also be true with omicron, which, incidentally, appears to be milder, so if you do get sick you’re less likely to end up in the hospital.
For people at high risk, more shots may be necessary—if someone who’s immunocompromised has little response to the vaccine at first, a fourth shot might help. But for everyone else, there’s likely little benefit to getting another dose so soon. (That’s not to say that we won’t all be getting more shots at a later date: Omicron-specific boosters might be on their way, and new COVID-19 vaccines could become a regular event, like flu shots, as we learn to live with the disease.)
Extra vaccine doses may not be harmful. Plotkin’s Vaccines, a massive reference book, says that mRNA vaccines, the type developed by Moderna and Pfizer-BioNTech, “at least in principle can be infinitely boostable,” Bar-Zeev says. That’s in contrast to earlier types of vaccines, which could suppress the immune response if the body is exposed repeatedly to a weakened virus; mRNA vaccines work differently by using genetic code to make the cells produce a protein. The vaccines can repeatedly boost antibodies.
“But just because you can, doesn’t mean you should,” Bar-Zeev says. Like any medicine, there’s some risk involved in taking a vaccine, and the long-term safety of fourth doses hasn’t been tested yet; people are taking that risk for what’s likely only a marginal benefit over a third dose.
An even bigger issue is that vaccines still aren’t available everywhere: Many people around the world have yet to get a single shot that might help protect them from severe illness and death. Last August, World Health Organization leader Tedros Adhanom Ghebreyesus called third booster shots immoral. “We’re planning to hand out extra life jackets to people who already have life jackets,” he said, while we’re leaving other people to drown without a single life jacket.”