Omicron evades immunity induced by Pfizer Inc.’s shot better than other Covid-19 variants, according to laboratory experiments that indicate a booster shot could help stop the highly mutated strain.

In the first reported experiments gauging the effectiveness of Pfizer and BioNTech SE’s vaccine, researchers at the African Health Research Institute found omicron infection results in about a 40-fold reduction in virus-blocking antibodies compared with the strain detected in China almost two years ago. The loss of immune protection is “robust, but not complete, said Alex Sigal, head of research at the Durban-based laboratory, in an online presentation late Tuesday.

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Since South Africa announced the discovery of omicron on Nov. 25, about 450 researchers globally have been working to isolate the highly mutated variant from patient specimens, grow it in the lab, verify its genomic sequence, and establish methods to test it in blood-plasma samples, according to the World Health Organization.

Omicron’s rapid spread in South Africa has raised concern that the immune protection generated by vaccination or a previous bout of Covid-19 may be insufficient to stop reinfections or stem a fresh wave of cases and hospitalizations. The WHO has warned omicron could fuel surges with “severe consequences amid signs that it makes the coronavirus more transmissible.

The work in Sigal’s lab involved testing blood plasma from people who were vaccinated against Covid-19 with the Pfizer-BioNTech shot to gauge the concentration of antibodies needed to neutralize, or block, the virus. The results, along with those from other labs currently under way, will help determine whether or not existing Covid vaccines need to be altered to protect against omicron.

Sigal’s laboratory was the first to isolate the beta variant, a strain of the coronavirus that was identified in South Africa in late 2020.

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