US President-elect Joe Biden has hailed as a “breakthrough” Pfizer’s announcement that its vaccine data suggests the shots may be 90 percent effective at preventing COVID-19. Biden on Monday congratulated those involved in giving the country “such cause for hope.”

But at the same time, Biden noted that the end of the battle against COVID-19 is still months away.

He said even if a vaccine is approved by the end of this month and some Americans are vaccinated later this year, it’ll be many more months before there’s widespread vaccination across the country.

Biden cited a warning by the head of the US Centers for Disease Control and Prevention that for the foreseeable future, a mask remains a more potent weapon against the virus than the vaccine.

“Today’s news doesn’t change this urgent reality,” Biden said, adding that Americans will have to rely on masking, distancing, social tracing, hand washing and other measures to keep themselves safe well into next year.

He said the US is still losing over 1,000 people a day from COVID-19 and will continue to get worse unless progress is made on mask-wearing and other actions.

Pfizer says an early peek at its vaccine data suggests the shots may be 90% effective at preventing COVID-19, indicating the company is on track later this month to file an emergency use application with US regulators.

Monday’s announcement doesn’t mean a vaccine is imminent. This interim analysis, from an independent data monitoring board, looked at 94 infections recorded so far in a study that has enrolled nearly 44,000 people in the US and five other countries.

Pfizer Inc. cautioned the initial protection rate might change by the time the study ends. Even revealing such early data is highly unusual.

Authorities have stressed it’s unlikely any vaccine will arrive much before the end of the year and limited initial supplies will be rationed.

The shots made by Pfizer and its German partner BioNTech are among 10 possible vaccine candidates in late-stage testing around the world – four of them so far in huge studies in the US

Another US company, Moderna Inc., also has said it hopes to be able to file an application with the Food and Drug Administration later this month.