An Israeli hospital said on Monday that preliminary research indicates that the fourth dose of the coronavirus vaccine provides only limited defense against the worldwide Omicron variant.
Shiba Hospital last month began giving the fourth vaccine to more than 270 medical workers — 154 who received the Pfizer-BioNtech vaccine and 120 others who received Moderna. All had previously been vaccinated three times with the Pfizer-BioNTech vaccine.
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The clinical trial found that both groups showed a “slightly greater” increase in antibodies than those following the third vaccine last year. But it said the increased antibodies did not stop the spread of Omicron.
“Despite increased antibody levels, the fourth vaccine only provided partial defense against the virus,” said Dr. Gili Regev-Yochay, director of the hospital’s Infectious Diseases Unit. “The vaccines, which were more effective than the previous variants, offer less protection versus Omron.”
Preliminary results raised questions about Israel’s decision to offer a second booster shot – and fourth overall – to a population over 60. The government says more than 500,000 people have received a second booster in recent weeks.

Dr Nahman Ashe, director of Israel’s health ministry, said the research did not mean the fourth vaccine attempt was a mistake. “It returns the level of antibodies at the beginning of the third booster. This is of great importance, especially among the older population,” he told Channel 13 TV.
But he said the research will be taken into account as officials debate whether to expand the additional booster campaign to a wider population.
Israel was one of the first countries to widely vaccinate its population last year and last summer became the first to offer a booster shot. The latest booster campaign for old Israelites is also believed to be the first of its kind in the world.
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Israel’s aggressive vaccination efforts have not been able to stop Omicron’s outbreak in recent weeks. The version has caused record-setting infection levels and sent increasing numbers of people to the hospital, although the number of seriously ill people is down from previous waves.
It has also forced large numbers of Israelis into quarantine, strained schools and businesses.
Omicron is already effective in many countries and can also infect people who have been vaccinated or were previously infected with earlier versions of the virus. However, early studies suggest it is less likely to cause severe disease than the previous delta variant. Vaccinations and boosters still provide strong protection against serious illness, hospitalization, and death.
On Tuesday, the Israeli government said it was reducing the mandatory quarantine period from seven days to five days to help keep the economy running.
Prime Minister Naftali Bennett said, “This decision will enable us to continue to protect public health on the one hand and the economy on the other, even if it is difficult, so that we can get out of this wave safely.” ,
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