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A fourth shot of the COVID-19 vaccine boosts antibodies but doesn't provide enough protection to prevent infections from the Omicron variant, according to new research at an Israeli hospital.
The preliminary results, released on Monday, challenge the idea of giving a second booster dose to slow the spread of the coronavirus, according to USA Today.
"Despite increased antibody levels, the fourth vaccine only offers a partial defense against the virus," Gili Regev-Yochay, MD, director of the hospital's infection prevention and control units, told reporters.
"The vaccines, which were more effective against previous variants, offer less protection versus Omicron," she said.
In a clinical trial, 274 medical workers at Sheba Medical Center near Tel Aviv received a fourth vaccine dose in December — 154 got the Pfizer vaccine and 120 got the Moderna vaccine — after previously getting three Pfizer shots.
Both groups received a boost in antibodies that was "slightly higher" than after the third shot, Regev-Yochay said. But when compared with a control group that didn't receive the fourth dose, the extra boost didn't prevent the spread of Omicron.
"We see many infected with Omicron who received the fourth dose," Regev-Yochay said. "Granted, a bit less than in the control group, but still a lot of infections."
Some public health officials in Israel say the campaign for fourth doses is still worthwhile, according to The Times of Israel. The vaccine still works well against the Alpha and Delta variants, Regev-Yochay said, and a fourth shot should go to older adults and those who face higher risks for severe COVID-19.
Hours after releasing the preliminary results, Sheba Medical Center published a statement calling for "continuing the vaccination drive for risk groups at this time, even though the vaccine doesn't provide optimal protection against getting infected with the variant." News outlets reported that the hospital was pressured into issuing the statement after Israel's Health Ministry didn't like the release of the early study results, The Times of Israel reported.
The second booster "returns the level of antibodies to what it was at the beginning of the third booster," Nachman Ash, MD, director of Israel's Health Ministry, told Channel 13 TV in Israel, according to The Associated Press.
"That has great importance, especially among the older population," he said.
As of Sunday, more than 500,000 people in Israel had received fourth doses since the country began offering them last month to medical workers, immunocompromised patients, and people ages 60 years and older, the AP reported. At the same time, the country has faced a recent coronavirus surge that has led to record-breaking numbers of cases and rising hospitalizations.
On Tuesday, the Israeli government said it would shorten the mandatory quarantine period from 7 days to 5 days, the AP reported.
"This decision will enable us to continue safeguarding public health on the one hand and to keep the economy going at this time on the other, even though it is difficult, so that we can get through this wave safely," Prime Minister Naftali Bennett said.
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Cite this: Carolyn Crist. Fourth Vaccine Shot Less Effective Against Omicron, Israeli Study Says - Medscape - Jan 18, 2022.