Pfizer Inc. and BioNTech SE’s COVID-19 vaccine may protect against the new fast-spreading variants of the coronavirus that have emerged in the U.K. and South Africa, according to a study.

The study, by researchers at the University of Texas Medical Branch and supported by the companies, homed in on the crucial N501Y mutation in the virus’s spike protein that is common to both fast-spreading variants. Antibodies in the blood of people who had been vaccinated were able to neutralize a lab-created version of the mutant virus.

Though it’s early data, the results are a promising sign that the vaccine will probably have an effect against the new variants, a major worry for health authorities that are struggling to stem a tide of new infections even as they seek to vaccinate hundreds of thousands of vulnerable people. Both the U.K. and South African strains appear to be more infectious than previous mutations.

The research examined the response to the mutant viruses in blood samples taken from 20 people who had gotten the companies’ mRNA vaccine as part of a previous clinical trial. The research didn’t study other mutations in the spike protein. Still, the antibodies in the vaccinated people’s blood did just as good a job at disarming the mutant virus as they did with the non-mutant version.

EU Secures an Additional 300 Million Pfizer Vaccine Doses

“This is clearly a positive, but there are important caveats to add,” Adam Barker, a London-based analyst with Shore Capital Group Ltd., wrote in a note. The study only addresses one mutation and doesn’t show whether the vaccine can actually prevent people from being infected with the new variant, he wrote. “That being said, the working assumption remains that vaccines will be at least partly effective against the novel variants.”

The findings were also consistent with the results of tests on 15 other mutations that have been found in SARS-CoV-2 strains, the researchers said.

“We are encouraged” by the early findings, Pfizer Chief Executive Officer Albert Bourla said in a tweet.

We are encouraged by early in vitro study findings that show the sera from people who have received the Pfizer-BioNTech #COVID19 vaccine effectively neutralized a SARS-CoV-2 virus having one of the mutations also found in two highly transmissible strains. 

Executives at BioNTech -- as well as from Moderna Inc., the developer of a rival mRNA shot -- had previously said they believed their vaccines would protect against the new strains. The University of Texas study is one of the first to back up those claims. The results were released on the bioRxiv preprint server early Friday, ahead of peer review.

The research comes as COVID-19 spreads globally at record daily levels, likely accelerated by the new strains, and as countries begin to roll out vaccines. The U.K. variant, which has been identified across the U.S. as well as in countries from South Korea to Canada, is thought to be 57 per cent to 70 per cent more transmissible than other strains of the virus.

Viruses have the opportunity to change through mutations that arise naturally as they replicate and circulate in their hosts. Some, like influenza, evolve quickly with thousands of mutations and distinct lineages, while others are more stable.