Pfizer's COVID-19 vaccine is 91% effective after six months and 100% effective against serious cases of the virus, news reports said Friday quoting data from third phase clinical trials.

The new long-term results could help Pfizer as the pharmaceutical company seeks an expansion of the vaccine's regulatory status. In a statement, Pfizer CEO Albert Bourla said the results "position us to submit a Biologics License Application to the U.S. Food and Drug Administration."

The results were taken from a new study of a 46,000-patient trial. Pfizer's COVID-19 vaccine has already been given to almost 80 million Americans.

The six-month result is only a little lower compared to the 95% efficacy rate that was first found for the vaccine, based on a much shorter term outcome.

Vaccine experts say protection from the disease can even last longer, but they say having data that shows good protection for up to six months after people were immunized is good news.

No safety issues were identified among the patients 16 years or older over at least six months' follow-up following the second shot, the Center for Infectious Disease Research and Policy said.

"So we know that immunity will not be short-lived," Dr. Peter Hotez, dean of the school of tropical medicine at Baylor College of Medicine, told CNN.

Dr. Anthony Fauci, chief of the National Institute of Allergy and Infectious Diseases, agreed that protection from these vaccines is likely to last longer than six months.

Pfizer is expected to apply to the U.S. Food and Drug Administration soon for full licensing of its COVID-19 vaccine.

All three available COVID-19 vaccines in the U.S., from Pfizer-BioNTech, Moderna and Johnson & Johnson, are being distributed under emergency use authorization (EUA) rather than full Food and Drug Administration licenses.