NEW YORK — Pfizer says its vaccine continues to be effective against COVID-19 up to six months later.

Pfizer and its German partner, BioNTech, announced updated results Thursday from their ongoing late-stage study of more than 44,000 volunteers.

The companies said the vaccine was 91% effective against symptomatic disease and was even more protective in preventing severe disease. Of 927 confirmed COVID-19 cases detected through March 13, 77 were among people who received the vaccine, and 850 were among people who got dummy shots.

“To have it at that high of a rate against what we’re really concerned about with hospitalizations and ICU visits — the things that have really crippled us as a society — to be able to have something that maintains that level over a long period of time is thrilling,” said Tamara Sheffield, MD, who is community health and prevention director with Intermountain Healthcare.

There were no serious safety concerns and the vaccine also appeared to work against a variant first detected in South Africa, the companies said.

“The South African variant, which other vaccines have had some trouble with, it’s performing very well,” said Sheffield.

It’s also performing well based on previous data against the U.K. variant, she added.

As time passes, we’ll all know more about just how long protection lasts — but Sheffield says there is real optimism about protection for a long time.

“We are expecting that, with it staying this high, that we will be even beyond six months,” said Sheffield.

The U.K. and the U.S. gave the emergency green light to roll out Pfizer’s vaccine late last year followed by many other countries. The vaccine is authorized for ages 16 and up.

This week, the companies said the vaccine is safe and strongly protective in kids as young as 12, based on a study of 2,260 U.S. volunteers.