COVID-19 cases in other countries are rising. How worried should the US be?

Commuters exited a Transport for London (TfL) London Overground train service from Walthamstow, after arriving at Liverpool Street station in London.TOLGA AKMEN/AFP via Getty Images

COVID-19 cases in the United Kingdom and a number of other European countries are on the rise again, and experts are eyeing the increases warily, wondering what’s in store in coming weeks for the United States.

“It’s certainly a bit worrisome. We definitely need to keep an eye on it, with the realization that the pandemic’s not over, unfortunately, as much as we all wish it were,” said Andrew Lover, an assistant professor of epidemiology in the School of Public Health and Health Sciences at UMass Amherst.

Lover said surges in Europe in the past have been followed by surges in the United States weeks or months later.

“We have to expect that we’ll see an uptick. It’s hard to tell whether it will be a minimal speed bump or something a bit more serious,” Lover said. “I think we should definitely prepare and be pleasantly surprised if it doesn’t happen.”

The United Kingdom has seen an increase in both cases and hospitalizations, while the US numbers have been declining from January peaks.

Other European countries have also seen COVID-19 rebounding, including Austria, the Netherlands, Switzerland, Germany, and Greece.

“I think people should be moderately worried and maybe it’s time to be cautious,” said Justin Lessler, a public health researcher at the University of North Carolina at Chapel Hill. “I certainly might think twice about putting down that mask. Keeping those precautions for a little bit longer may make sense.”

Matthew Fox, a professor of epidemiology and global health at the Boston University School of Public Health, said in an e-mail, “We should be vigilant.”

He said what he was “really focused on is not whether [cases] go up, because we will see more waves, but a) whether these are big waves or small ones and b) whether they are associated with increases in hospitalizations like in prior waves. If they are associated with less hospitalization, it may mean we’ve reached a stage where we just monitor things. If they are not, we might need more action.”

Experts are also pointing to wastewater surveillance data gathered from around the United States by the US Centers for Disease Control and Prevention. The data are considered an early warning signal for COVID-19 case increases. More than a third of collection sites nationwide saw an increase in levels of SARS-CoV-2 RNA over a recent 15-day period.

Dr. Eric Topol, a cardiologist and the founder and director of the Scripps Research Translational Institute, has been posting tweets about the increases in recent days, saying, “The next wave in Europe has begun” and warning, “What happens in the UK and Europe doesn’t stay there.”

“Based on European case increases, the US could see a new rise in COVID cases over the Spring,” Andy Slavitt, a former White House pandemic adviser, tweeted Monday, suggesting that the highly transmissible Omicron subvariant BA.2 is driving the growth.

Asked about Slavitt’s tweets at a White House media briefing Monday, press secretary Jen Psaki said authorities have been watching BA.2 closely. “We currently have about 35,000 cases [reported daily] in this country. We expect some fluctuation, especially at this relatively low level, and, certainly, that to increase.”

She emphasized that “the tools we have — including mRNA vaccines, therapeutics, and tests — are all effective tools against the virus,” but also warned that continued funding was needed to battle the pandemic. The Biden administration has been warning that funds will soon run out for future booster shots, new treatments, and testing efforts if spending legislation remains stuck in Congress, NBC News reported Tuesday.

Dr. Scott Gottlieb, former commissioner of the US Food and Drug Administration and a Pfizer board member, has been sanguine about the future. He tweeted Monday, “While we’re likely to see some flattening in the drop in daily cases, and possibly a short spike in new cases -- owing to rising BA.2, relaxed mitigation, and some immunity waning -- it’s unlikely to be the start of a new surge, and prevalence should resume declines into the summer.”

Dr. Anthony Fauci, the nation’s top infectious disease doctor, told CNN that US officials were “keenly interested” in what is going on in the United Kingdom.

He told the network that he had spoken with his UK counterparts, and they attributed the case spike to a combination of three factors, which, in order of contribution, were: the rise of BA.2, the reopening of society, and people’s waning immunity from vaccination or prior infection.

“Without a doubt, opening up society and having people mingle indoors is clearly something that is a contributor, as well as overall waning immunity, which means we’ve really got to stay heads-up and keep our eye on the pattern here,” Fauci said. “So that’s the reason why we’re watching this very carefully.”

BA.2 has been growing in prevalence in the United States, accounting for 23.1 percent of cases nationally as of March 12, according to CDC estimates, and 38.6 percent in New England. Across the United States, pandemic restrictions have also been lifted in the wake of the winter surge.

Concerns about waning immunity from shots have sparked discussions of the possible need for second booster shots. The Washington Post reported Tuesday that Pfizer planned to seek authorization for second boosters for those 65 and older.

William Hanage, an epidemiology professor at the Harvard T.H. Chan School of Public Health, said what happens in Europe offers a “glimpse of a possible future.”

He said it was “reasonable to suggest that ... we’re going to see an uptick in at least some places,” but it wasn’t clear if BA.2 would sweep across the nation as the original Omicron did.

“The only thing I’m very prepared to predict is that places with large quantities of unboosted, unvaccinated older folks are going to have a much more consequential experience with BA.2,” he said.

In Massachusetts, COVID-19 cases and hospitalizations have been dropping since the peak earlier this year but the pace of decline has slowed.

Levels of SARS-CoV-2 RNA detected in wastewater, after dropping precipitously, have been fluctuating at a relatively low level.

What should people do in anticipation of a BA.2 uptick?

Lessler said, “I’m hopeful that this is not going to be a big deal for the US, but certainly the signs from Europe are worrying. And if it does look like something is coming, the same things that have always kept us safe are things that will work now.” Wearing masks, avoiding mass gatherings, and getting vaccinated “are still the best things to do,” he said.