The ongoing Phase 3 clinical trial of Pfizer/BioNTech's coronavirus vaccine confirms its protection remains high for at least six months after the second dose, the companies said Thursday.

Protection likely lasts even longer than that, vaccine experts say, but they say having data showing good protection six months after people were vaccinated is good news. The vaccine remains more than 91% effective against disease with any symptoms for six months, the companies said in a statement. And it appeared to be fully effective against the worrying B.1.351 variant of the virus, which is the dominant strain circulating in South Africa and which researchers feared had evolved to evade the protection of vaccines, the companies said.

"The vaccine was 100% effective against severe disease as defined by the U.S. Centers for Disease Control and Prevention (CDC), and 95.3% effective against severe COVID-19 as defined by the U.S. Food and Drug Administration (FDA)," Pfizer and BioNTech said in a joint statement.

The findings indicate protection will last even longer than six months, vaccine experts said.
"The information coming from Pfizer-BioNTech is good news with evidence that those enrolled in the clinical trials last year are still protected. So we know that immunity will not be short-lived," Dr Peter Hotez, a vaccine expert and dean of the school of tropical medicine at Baylor College of Medicine, told CNN.

"Hopefully the protection might last years, but we won't know until we know."

On Wednesday, the companies said a small trial of volunteers aged 12 to 15 showed 100% efficacy in that age group.
"These data confirm the favourable efficacy and safety profile of our vaccine and position us to submit a Biologics License Application to the U.S. FDA," Albert Bourla, Pfizer's chairman and chief executive officer, said in a statement. A BLA is an application for full approval. The vaccine currently has emergency use authorization, EUA, which falls short of full approval.