Europe and Brazil are getting slammed by COVID-19 again. The U.S. is in better shape but not immune.

"Optimism is spreading in the U.S. as COVID-19 deaths plummet and states ease restrictions and open vaccinations to younger adults," The Associated Press reports. "But across Europe, dread is setting in with another wave of infections that is closing schools and cafes and bringing new lockdowns."

"Each of these countries has had nadirs like we are having now, and each took an upward trend after they disregarded known mitigation strategies," Dr. Rochelle Walensky, director of the U.S. Centers for Disease Control and Prevention, said Monday. "They simply took their eye off the ball." Health experts say America's much more successful vaccination campaign could blunt a Europe-like resurgence, but the U.S. should also view Europe as a cautionary tale.

Brazil is also being roiled by its worst COVID-19 outbreak yet, CNN reports.

And the U.S. isn't immune — yet. "After weeks of declining coronavirus deaths and hospitalizations, new hot spots of infection have emerged" in the Northeast, Upper Midwest, and Mid-Atlantic states, The Washington Post reports. A majority of Americans 65 and over have been vaccinated, which should keep the hospitalization and fatality numbers down, but the variants — especially the more contagious, deadlier B.1.1.7 strain first found in Britain — are a worrisome wild card.

Europe didn't get slammed until more than half of new cases were from the U.K. variant, University of Minnesota infectious disease expert Michael Osterholm tells the Post. "What Europe is telling us is that we haven't yet begun to see the impact of B.1.1.7 here." America's best option, health experts say, is combining mitigation measures — masks, social distancing, vigilance — with an urgent vaccination effort.

"I think it is a race against time," Dr. Stephen Thomas at Upstate Medical University tells The New York Times. "Every single person that we can get vaccinated or every single person that we can get a mask on is one less opportunity that a variant has." Dr. Amesh Adalja at the Johns Hopkins Center for Health Security agrees. "Vaccination with no speed limit, 24/7, that's what's going to protect us from what's happening in Europe," he told AP.

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