As the more transmissible Delta variant spreads throughout the US, President Joe Biden is scrambling to find ways to get more Americans vaccinated, including going door-to-door

In a press briefing on Tuesday, Biden said mass vaccination sites across the country are closing down, and now “we need to go to community by community, neighborhood by neighborhood, and oftentimes, door to door – literally knocking on doors – to get help to the remaining people protected from the virus.”

Experts have said communities with the least vaccination rates are more at risk of outbreaks caused by the more transmissible Delta variant, which originated in India. The variant may also be able to evade protection from existing vaccines, as Insider’s Aria Bendix reported.

The variant has already been found in all 50 states and is dominant in five, including California. It’s expected to be the most dominant strain in the country in the coming weeks.

Delta poses the most risks to the unvaccinated. A recent Associated Press analysis found almost all of the COVID-19 deaths in the US are among those who are unvaccinated

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“Our fight against this virus is not over,” Biden said. “Right now, as I speak to you, millions of Americans are still unvaccinated and unprotected. And because of that, their communities are at risk, their friends are at risk. The people that they care about are at risk.”