An Israeli hospital on Monday said preliminary research indicates a fourth dose of the coronavirus vaccine provides only limited defense against the Omicron variant that is raging around the world.
Sheba Hospital last month began administering a fourth vaccine to more than 270 medical workers — 154 who received a Pfizer-BioNtech vaccine and 120 others who received Moderna's. All had previously been vaccinated three times with the Pfizer-BioNtech vaccine.
The clinical trial found that both groups showed increases in antibodies "slightly higher" than following the third vaccine last year. But it said the increased antibodies did not prevent the spread of Omicron.
The preliminary results raised questions about Israel's decision to offer a second booster shot — and fourth overall — to its over-60 population. The government says over 500,000 people have received the second booster in recent weeks.
Israel was one of the first countries last year to widely vaccinate its population and last summer became the first to offer a booster shot. The latest booster campaign for older Israelis also is believed to be the first of its kind in the world.
Israel's aggressive vaccination efforts have not been able to stop an Omicron outbreak in recent weeks. The variant has caused record-setting infection levels and sent a growing number of people to the hospital, though the numbers of seriously ill remain below previous waves.
Omicron is already dominant in many countries and can also infect those who have been vaccinated or had previously been infected by prior versions of the virus. Early studies, however, show it is less likely to cause severe illness than the previous Delta variant. Vaccination and a booster still offer strong protection from serious illness, hospitalization and death.
Additional reporting by The Associated Press.