Pfizer (PFE) and BioNTech's (BNTX) COVID-19 vaccine is proving effective six months after the second dose, according to an ongoing analysis of the Phase 3 trial participants.

The vaccine showed 91.3% efficacy against COVID-19, slightly lower than the original 95% seen in Phase 3 trials.

The data, from 12,000 of the more than 44,000 adults in the trial, is a result of observations from seven days through six months after the second dose was received.

The two companies announced the results in a statement Thursday, with plans to provide the detailed data to global regulatory bodies, including the U.S. Food and Drug Administration (FDA).

Of note was the vaccine's efficacy in South Africa, where the B.1.351 variant originated. Among the more dominant strains globally, the B.1.351 has shown the most reduction in vaccine efficacies both in Phase 3 trials and in labs.

The Pfizer/BioNTech was 100% effective in preventing COVID-19 cases in South Africa, according to the companies.

Pfizer CEO Albert Bourla said in a statement, "The high vaccine efficacy observed through up to six months following a second dose and against the variant prevalent in South Africa provides further confidence in our vaccine’s overall effectiveness.”

Health experts have in recent months pointed to a vaccine's ability to prevent severe disease and hospitalization as a more important metric.

Phase 3 results initially showed the vaccine protected mostly against severe disease, with one case observed in the vaccinated group. In the statement Thursday, the companies said the vaccine was 100% effective against severe disease as defined by the Centers for Disease Control and Prevention (CDC), and 95% based on the FDA's definition.

BioNTech CEO Ugur Sahin said the results provide further confidence for global vaccination efforts.

“These data also provide the first clinical results that a vaccine can effectively protect against currently circulating variants, a critical factor to reach herd immunity and end this pandemic for the global population," he said in a statement.

The statement of the new data comes a day after the companies revealed strong results from a trial of adolescents aged 12 to 15 years old. Once submitted to the FDA, the companies anticipate authorization to vaccinate individuals in the age group before the start of the new school term in fall.

Moderna's new trial

Meanwhile, Moderna (MRNA) has begun a new trial to test a vaccine specifically targeting the worrisome B.1.351 variant.

The new Phase 1 trial, in collaboration with the National Institute of Allergy and Infectious Diseases, will enroll 210 adults in Atlanta, Cincinnati, Nashville and Seattle. It will include adults 18 and older that have received a COVID-19 vaccine, as well as adults 18-55 who have not.

“The B.1.351 SARS-CoV-2 variant, first identified in the Republic of South Africa, has been detected in at least nine states in the United States,” said NIAID director Dr. Anthony Fauci, in a statement.

“Preliminary data show that the COVID-19 vaccines currently available in the United States should provide an adequate degree of protection against SARS-CoV-2 variants. However, out of an abundance of caution, NIAID has continued its partnership with Moderna to evaluate this variant vaccine candidate should there be a need for an updated vaccine," he said.

More from Anjalee:

• Novavax CEO: If FDA waits for US data, 'the lag will be a couple of months' for its vaccine

• China, Russia playing 'greater-than-expected' roles in global pandemic response

• Biden COVID-19 adviser: Vaccine news is great, but we still have a ways to go

Read the latest financial and business news from Yahoo Finance.

Follow Yahoo Finance on Twitter, Facebook, Instagram, Flipboard, SmartNews, LinkedIn, YouTube.

Follow Anjalee on Twitter @AnjKhem.