Company researchers observed a 25-fold reduction in neutralizing antibody levels versus the variant, compared with the original strain of the virus, in people who got just two shots. However, boosting with an additional shot of the vaccine raised antibodies 25-fold against Omicron, giving a similar level of the protective proteins as observed against those earlier versions after the standard two doses, the vaccine partners said in a statement. 

The lab findings indicate that two doses of the vaccine “may not be sufficient” to protect against infection with the Omicron strain, the companies said in a release. Along with stimulating the booster push, that may increase the likelihood that an Omicron-targeted shot may ultimately be required. Pfizer said this would be ready by March.

Uncertainty over vaccine efficacy against the new variant has fueled market volatility and prompted travel restrictions since Omicron was identified in southern Africa last month. News of the study outcome helped buoy the U.S. stock market, with S&P 500 futures gaining 0.2%. Pfizer shares gained 0.5% in pre-market trading in New York, while BioNTech American depositary receipts rose 3%. 

The Pfizer-BioNTech results add to data from around the world attempting to assess the impact of Omicron on vaccine protection. South African researchers found a 41-fold drop in levels of virus-blocking antibodies against Omicron, compared with the strain circulating at the start of the pandemic. A German team found a 37-fold drop in antibodies against Omicron versus the highly transmissible Delta variant. 

Watching closely

However, a study from Stockholm’s Karolinska Institute was more optimistic, finding the decline in antibodies against Omicron was only slightly worse than for Delta. T cells, another virus-fighting component of the immune system, should still be able to respond to Omicron. About 80% of viral features called epitopes that are recognized by T cells are unchanged in the variant, Pfizer and BioNTech said.

The companies said they’ll be watching closely to see how quickly immunity against Omicron wanes over time even after a third dose.  

“It’s clear from these preliminary data that protection is improved with a third dose,” Pfizer Chief Executive Officer Albert Bourla said in the statement. 

Boosters could help people everywhere “get through the winter season” as the companies work on adapting the vaccine, BioNTech CEO Ugur Sahin said. An adapted vaccine should provide “a prolonged protection compared to the current vaccine,” he said. 

—With assistance from Robert Langreth and Jason Gale.