Dr. Anthony Fauci says he's hopeful a COVID-19 vaccine could be available for children under 5 next year, but studies can't be rushed, making an exact timeline uncertain.

"Hopefully within a reasonably short period of time, likely the beginning of next year in 2022, in the first quarter of 2022, it will be available to them," Fauci told Insider, adding, "Can't guarantee it, you've got to do the clinical trial."

Pfizer's pediatric vaccine trials are already underway. The company estimates it could have early results for young children ages 2-4 by the end of the year, meaning authorization is possible sometime next year. Moderna is further behind, but also has ongoing trials in children as young as six months.

Clinical trials don't always unfold on a predictable timeline, and experts emphasize studies in young children won't be rushed.

-ABC News' Cheyenne Haslett, Sony Salzman

The FDA on Friday said it has authorized Pfizer and Moderna boosters for all adults, six months after the second shot.

“With boosters, more adults will now have the opportunity to help preserve a high-level of protection against this disease," Pfizer CEO Albert Bourla said in a statement.

“This emergency use authorization comes at a critical time as we enter the winter months and face increasing COVID-19 case counts and hospitalizations across the country,” Moderna CEO Stéphane Bancel said in a statement.

As for next steps, the CDC's independent advisory committee is meeting Friday afternoon to discuss boosters for all.

CDC director Rochelle Walensky will issue CDC recommendations, which is the last step in the regulatory process.-ABC News' Cheyenne Haslett

Austrian Chancellor Alexander Schallenberg announced Friday that the country will go into a full nationwide lockdown to curb a fourth wave of COVID-19 infections.

"We do not want a fifth wave," Schallenberg warned.

The lockdown will begin Monday and last for at least 10 days before the situation is reassessed. If the number of new COVID-19 cases has not dropped significantly, the lockdown can be extended to a maximum of 20 days.

Under the restrictions, people will be told to work from home, non-essential shops will close and public gatherings will be canceled. Schools will remain open for students who require in-person learning, but parents have been asked to keep their children at home if possible.

COVID-19 vaccination will also become mandatory by law in Austria, starting on Feb. 1.

It's the first country in Europe to make COVID-19 vaccines compulsory and the first to reimpose a full lockdown this winter, as the continent grapples with rising infections.

The Austrian government had initially imposed a nationwide lockdown only for the unvaccinated that began last Monday.

Mask-wearing cuts COVID-19 incidence by 53%, according to a new analysis that pooled results from multiple studies.

The analysis, published Thursday in the medical journal The BMJ, found that mask-wearing, social distancing and hand-washing were all effective in reducing the spread of COVID-19.

The bulk of the studies included in the analysis were conducted before mass vaccinations. The researchers, who were from several universities in Australia, Scotland and China, said that more studies are needed to understand the effectiveness of these public health measures in the context of widespread vaccination coverage.

-ABC News' Guy Davies, Esra Demirel and Sony Salzman