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Pfizer-BioNTech's COVID-19 vaccine appeared to be 100% effective at preventing cases of the South African variant, B.1.351, the .

Topline results from a phase III clinical trial of 800 people in South Africa, where the variant is predominant, showed nine cases in the placebo group versus none among vaccine recipients, for a vaccine efficacy of 100%, albeit with a wide 95% confidence interval (lower bound 53.1%).

Prior data, the companies acknowledged, were from laboratory immunogenicity studies, demonstrating that the vaccine induced broadly neutralizing antibody responses against the variant in vitro, although with lower responses than to the wild-type strain.

In addition, Pfizer and its German partner touted topline data from its 46,307-person phase III trial through March 13, 2021, showing 91.3% efficacy against symptomatic illness 7 days after the second dose (95% CI 89.0%-93.2%), 100% efficacy against CDC-defined severe illness (95% CI 88.0%-100%), and 95.3% efficacy against severe illness as defined by the FDA (95% CI 71.0%-99.9%).

These data came after 927 confirmed cases of symptomatic COVID-19 occurred in the ongoing trial, which began last summer, including 850 in the placebo group and 77 in the vaccine group. Of these, 697 cases were in the U.S. (647 in the placebo group vs 50 in the vaccine group), for a U.S. vaccine efficacy of 92.6% (95% CI 90.1%-94.5%).

There were 32 cases of severe disease as defined by the CDC in the placebo group versus none in the vaccine group, and 21 severe cases as defined by the FDA in the placebo group versus one in the vaccine group.

Importantly, Pfizer and BioNTech now have 6 months of safety data on the product, which for a COVID-19 vaccine to be considered for full licensure.

Pfizer CEO Albert Bourla made it clear in a statement that the company will be pursuing that goal: "These data confirm the favorable efficacy and safety profile of our vaccine and position us to submit a Biologics License Application to the U.S. FDA."

The release noted that there were no serious safety concerns 6 months after the second dose, with results generally consistent with previously reported data. The manufacturer said it has now evaluated vaccine safety in 44,000 participants ages 16 and older, and 12,000 vaccinated participants have at least 6 months of follow-up.

Pfizer and BioNTech said they would submit the new findings to a peer-reviewed journal for publication.

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