Jerusalem, Jan 18 (IANS): After becoming the first country to roll out a fourth dose of Covid vaccine, a study conducted in Israel now says that the second booster shot is not enough to fight the Omicron variant.

According to experts at the Sheba Medical Centre, which launched a trial in December 2021 to test the efficacy of a fourth Covid shot, although the booster raises antibody levels, there are "still a lot of infections" among those who received it, The Times of Israel reported.

The second booster was only partially effective in protecting against the Omicron strain, which has the potential to escape vaccine immunity.

"The vaccine, which was very effective against the previous strains, is less effective against the Omicron strain," Prof. Gili Regev-Yochay, a lead researcher in the experiment was quoted as saying.

"We see an increase in antibodies, higher than after the third dose."

"However, we see many infected with Omicron who received the fourth dose. Granted, a bit less than in the control group, but still a lot of infections.

"The bottom line is that the vaccine is excellent against the Alpha and Delta (variants), for Omicron it's not good enough," she said.

Lasr December, Israel began offering fourth vaccine shots to people aged 60 and older, the immunocompromised, and medical workers.

While Regev-Yochay noted that it is still probably a good idea to give a fourth shot to those at higher risk, but should only include even older groups than just over 60s. However, she did not elaborate, the report said.

Despite the lack of proper data, Israel pushed ahead with expanding the fourth dose programme.

As of Sunday night, over 500,000 Israelis have been inoculated with a fourth dose, the report said.

Many countries, including Chile and Denmark, have followed suit, while some like Germany and France are considering it.

Meanwhile, the World Health Organization has urged countries to delay booster programmes until the whole world has access to initial vaccine doses.