Even a fourth shot of a COVID-19 vaccine is “not good enough” to prevent Omicron, according to a preliminary study in Israel.

Sheba Hospital last month tested a fourth shot given to more than 270 medical workers, with 154 getting the Pfizer jab and 120 receiving Moderna.

The researchers revealed Monday that both groups showed a “slightly higher” increase in antibodies than after the third shot — but still not enough to prevent Omicron, the latest variant responsible for the vast majority of infections around the world.

“Despite increased antibody levels, the fourth vaccine only offers a partial defense against the virus,” said Dr. Gili Regev-Yochay, director of the hospital’s infection disease unit leading the study.

The study saw “many infected with Omicron who received the fourth dose,” she said. “Granted, a bit less than in the control group, but still a lot of infections.”

“The vaccines, which were more effective against previous variants, offer less protection versus Omicron,” Regev-Yochay said, adding that the vaccines are “not good enough” to prevent the less-severe new variant.

The findings have not yet been published and do not reveal specific data.

But the study raised questions about Israel’s decision to be the first in the world 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. But the country has still seen record-high infections recently, even though 80 percent of Israel’s adult residents have received two shots and more than half have gotten boosted.

Hours after releasing the results, Sheba Hospital called for “continuing the vaccination drive … even though the vaccine doesn’t provide optimal protection against getting infected with the variant.”

Hebrew media reported that the hospital was pressured into issuing that statement after the Health Ministry didn’t like the study’s results, according to the Times of Israel.

Dr. Nahman Ash, director of Israel’s Health Ministry, also insisted that the findings did not mean the fourth-shot effort was a mistake.

“It returns the level of antibodies to what it was at the beginning of the third booster. That has great importance, especially among the older population,” he told Channel 13 TV.

On Tuesday, the Israeli government said it was shortening the mandatory quarantine period from seven days to five days in order to help keep the economy running.

“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,” said Prime Minister Naftali Bennett.

With Post wires