The Pfizer Inc.-BioNTech SE vaccine remained highly effective against COVID-19 after six months, according to new long-term results that Pfizer said could be used to seek an expansion of the shot’s regulatory status.

Follow-up data from a final-stage trial of 46,307 people showed the vaccine was 91.3 per cent effective in preventing symptomatic cases starting one week after the second dose through as long as six months. In the U.S. alone, the efficacy rate was 92.6 per cent, according to a report Thursday by the two companies.

At the same time, the companies provided some of the first data on how their vaccine might handle the immune-evading B.1.351 variant that arose in South Africa. Nine of 800 trial participants in that country got sick with COVID, including six infected with B.1.351. However, all were in the placebo group, suggesting the shot retains efficacy against the variant.

Albert Bourla, Pfizer’s Chief Executive Officer, said in the statement that the results “position us to submit a Biologics License Application to the U.S. FDA.”

The vaccine has already secured an emergency use authorization from the Food and Drug Administration, which means it’s only in effect until the emergency ends and it can be revoked or changed at any time. Formal approval is for the long term.

Pfizer shares were little changed at 10:48 a.m. in New York trading while BioNTech gained 3.5 per cent. The companies will soon share the data with regulators around the world and submit it for publication in a scientific journal, Pfizer spokeswoman Amy Rose said in an email.

The six-month result is only slightly lower than the 95 per cent efficacy rate that was originally found for the vaccine, based on much shorter term results. The two-shot vaccine also prevented all or nearly all severe cases of the disease over six months, depending on the exact definition used.

The companies said that no new serious safety concerns were identified.

The data was released in a joint company statement and hasn’t been independently reviewed and published in a scientific journal. Nonetheless, it provides an early reassuring sign that the vaccine’s strong efficacy seen in the short-term results will hold up and not fade away quickly.

Meanwhile, in a study in the U.K., the Pfizer-BioNTech vaccine generated strong antibody responses in 98 per cent of elderly people. The patients ages 80 to 96 were also able to mount a defense against the Brazil variant after two injections, although it was less robust, according to the research conducted by the University of Birmingham.