July 27, 2021 4:36 PM EDT

Two months ago, COVID-19 cases were down in 49 of 50 states. The number of Americans hospitalized by the virus was a quarter of the levels seen at the beginning of the year. Vaccinations were climbing steadily, and President Joe Biden announced on May 13 that vaccinated Americans didn’t need to wear masks. “Today is a great day for America in our long battle with coronavirus,” Biden said with a smile.

That battle is dragging out longer than Biden expected. Driven by a large segment of the country’s reluctance to get the vaccine shot and the virus’s delta variant spreading through the unvaccinated population, cases are now rising in every state. Hospitalizations from the virus—having fallen by half in June—are back up to the levels seen in May. That’s why on Tuesday, the Center for Disease Control and Prevention (CDC) had to walk back its earlier guidance and tell those who are vaccinated and living in states with high rates of infection to put their masks back on while indoors.

Dr. Rochelle P. Walensky, director of the CDC, said new science has shown that on “rare occasions” some vaccinated people may contract the delta variant and be contagious to others, even if their symptoms are mild. In “areas of substantial and high transmission,” people who have been vaccinated should wear their masks indoors at public events, Walensky said. The CDC recommends that K-12 schools in areas of high transmission rates should return to full-time, in-person learning in the fall and have teachers, staff and students wear masks indoors. Being vaccinated continues to be the best way to prevent dying or being hospitalized with severe disease when exposed to the virus, the CDC says.

The uptick in cases and the new medical guidance on mask wearing has put Biden into a tough spot. Biden and White House officials had wanted July to be a moment of reopening for the U.S. and a time for the economy to show signs it was moving past the pandemic. The virus hasn’t cooperated, and there are signs its resurgence comes with a political cost for Biden. Biden’s approval rating dropped to 50% in Gallup polling released on July 23, a dip from 56% in June. Biden is facing pressure from multiple sides. Americans of all political leanings are struggling to make sense of more than a year of morphing guidelines and rules. In the first weeks of the pandemic in the U.S., the CDC didn’t recommend face masks among the general public out of fear of a debilitating run on medical masks. Republican politicians have often chafed at wearing masks and sent mixed messages on how they should be used. (When Trump announced the CDC’s initial recommendation in April 2020 that all Americans should then wear masks in public, Trump himself said he wouldn’t be wearing one.) And just over two months ago, Biden said vaccinated individuals could stop wearing them.

Experts acknowledge the challenge of keeping up with what’s required to contain the virus. “It’s just a constant course correction,” says Andy Slavitt, who stepped down in June as Biden’s former senior advisor on the COVID response. “If you’re indoors with people whose vaccination status you don’t know, masking is going to continue to make sense as a good layer of protection.”

When asked Tuesday if the White House has a message to Americans feeling “whiplash” from the CDC’s updated guidance, White House Press Secretary Jen Psaki replied, “Our goal is to save their lives.”

Contributing to the spread of the new virus mutation, the vaccine rollout in the U.S. has started to plateau, with about 56% of Americans over the age of 12 fully vaccinated. The hesitation among the remainder has been fueled by months of skepticism amplified by right-wing media personalities and Republican politicians, some of whom have only recently begun to recommend others get vaccinated. Studies show the vaccines have dramatically reduced severe and deadly COVID-19 cases among those vaccinated, but federal scientists are concerned that the increasing practice of not wearing masks inside has allowed the virus to spread, contributing to its mutation into new strains, including the delta variant that now makes up over 80% of new cases in the U.S. The delta variant of the virus continues to show “its willingness to outsmart us and be an opportunist,” Walensky said.

To address the slowing pace of vaccinations, the Biden Administration has rolled out expansive community outreach programs. It’s also turning to new requirements for the federal workforce. The Biden Administration decided Monday to require all health care workers in Veterans Administration facilities be vaccinated, and officials are looking at other vaccine requirements for federal workers and facilities. Other agencies are looking closely at whether to require federal workers to be vaccinated, White House officials said. Slavitt suggests that every employer, school and city should be thinking about requiring people to show they are vaccinated or have recently tested negative for COVID before opening up events. “The idea that there’s going to be a little bit of friction in your life if you are not willing to get vaccinated I think is part of what will help people think it through,” Slavitt says.

Federal scientists are concerned that if the virus continues to spread among unvaccinated Americans, a new mutation could emerge that could be deadly even to those already vaccinated. Wearing masks could help prevent that, they argue. “The big concern is that the next variant that might emerge, just a few mutations potentially away, could potentially evade our vaccine,” Walensky said.

On Friday, White House officials convened a meeting that included national security officials, the Department of Transportation, the Department of Homeland Security, to discuss whether to reopen the U.S. to European travelers. Given the increase in infections, officials decided to keep COVID-19 travel barriers for Europe in place, a blow to American tourism and airline businesses. In addition, the U.S. Food and Drug Administration (FDA) is still in the process of giving full approval to the Pfizer, Moderna and Johnson & Johnson vaccines, a step that some hope would help allay concerns among those still hesitant to get the shots. Those vaccines are currently being administered under the FDA’s emergency use authorizations.

Without more Americans being vaccinated or continuing to wear masks, there could be more tough times ahead for Biden and for the country. “All the smug pronouncements have come smack dab into reality,” says Joe Grogan, who served as former President Donald Trump’s domestic policy advisor when the pandemic began spreading rapidly on U.S. shores last year. “The Biden Administration is finding out this is not easy.”

Correction, July 29

The original version of this story misstated the name of the U.S. Food and Drug Administration and incorrectly quoted Dr. Rochelle P. Walensky, director of the CDC. Walensky said the delta variant could potentially “evade” the vaccine, not “invade.”

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