sraeli healthcare workers who were boosted with a fourth shot of COVID-19 vaccine at the height of the Omicron wave were only marginally more protected against reinfection than their peers who had received three jabs of vaccine, researchers reported Wednesday.

Compared to getting two initial doses and one booster shot of Pfizer and BioNTech’s Comirnaty vaccine, adding a second booster shot reduced the rate of coronavirus infection by just 30%.

The fourth dose was somewhat more effective at preventing COVID-19 symptoms, according to a study published in the New England Journal of Medicine. The healthcare workers who got the second booster shot were 43% less likely to show signs of illness than were those who hadn’t.

Using Spikevax, Moderna’s COVID-19 vaccine, as a second booster shot was even less effective at preventing coronavirus infections in this group of younger, generally healthy Israelis. Recipients were only 11% less likely than those who had gotten three doses of vaccine to be reinfected during Israel’s Omicron wave, and they were 31% less likely to suffer symptoms of COVID-19.