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What Rising Covid-19 Infections In The UK And Europe Could Mean For The US

March 15, 2022 / 5:59 PM EDT / CBS Baltimore

(CNN) -- Two weeks after the United Kingdom dropped its last remaining Covid-19 mitigation measure -- a requirement that people who test positive for the virus isolate for five days -- the country is seeing cases and hospitalizations climb once again.

Covid-19 cases were up 48% in the UK last week compared with the week before. Hospitalizations were up 17% over the same period.

The country's daily case rate -- about 55,000 a day -- is still less than a third of the Omicron peak, but cases are rising as fast as they were falling just two weeks earlier, when the country removed pandemic-related restrictions.

Daily cases are also rising in more than half of the countries in the European Union. They've jumped 48% in the Netherlands and 20% in Germany over the past week, according to data from Johns Hopkins University. But daily cases in Germany had yet to drop below pre-Omicron levels, and the Netherlands hadn't seen cases fall as much as they did in the UK.

The situation in Europe has the attention of public health officials for two reasons: First, the UK offers a preview of what may play out in the United States, and second, something unusual seems to be happening. In previous waves, increases in Covid hospitalizations lagged behind jumps in cases by about 10 days to two weeks. Now, in the UK, cases and hospitalizations seem to be rising in tandem, something that has experts stumped.

"So we're obviously keenly interested in what's going on with that," Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, told CNN.

Fauci said he's spoken with his UK counterparts, and they have pegged the rise to a combination three factors. In order of contribution, Fauci said, these are:

The BA.2 variant, which is more transmissible than the original Omicron
The opening of society, with people mingling more indoors without masks
Waning immunity from vaccination or prior infection

In a technical briefing Friday, the UK Health Security Agency said BA.2 had an 80% higher relative growth rate than the original Omicron strain, though it does not seem more likely to lead to hospitalization.

Given that BA.2 doesn't seem to be causing more severe disease -- at least not in the highly vaccinated British population -- it's not clear why hospitalizations are ticking up.

"The issue with hospitalization is a little bit more puzzling, because although the hospitalizations are going up, it is very clear their use of ICU beds has not increased," Fauci said. "So are the numbers of hospitalizations a real reflection of Covid cases, or is there a difficulty deciphering between people coming into the hospital with Covid or because of Covid?"

The US, like the UK, has lifted most mitigation measures as Covid-19 infections have fallen. Two weeks ago, the US Centers for Disease Control and Prevention changed how it measures Covid-19 impact in communities. The new metric -- which relies on hospitalizations and hospital capacity in addition to cases -- did away with masking recommendations for most parts of the country. States and schools have followed suit, lifting indoor masking requirements.

READ: Your top Covid questions, answered

"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."

Michael Osterholm, who directs the Center for Infectious Disease Research and Policy at the University of Minnesota, told CNN, "it's like a weather alert. Right now, the skies are sunny and bright, and we hope they stay that way. But we could have some bad weather by evening, and we just don't know."

What will BA.2 do in the US?

BA.2 has been growing steadily in the US. Last week, the CDC estimated it was causing about 12% of new Covid-19 cases here.

Meanwhile, BA.2 now accounts for more than 50% of cases in the UK and several other European countries.

"The tipping point seems to be right around 50%," said Keri Althoff, an epidemiologist at Johns Hopkins Bloomberg School of Public Health. "That's when we really start to see that variant flex its power in the population" as far as showing its severity.

Althoff said although the UK may provide a glimpse of the future, there are key differences that will affect how BA.2 plays out in the United States.

In the UK, 86% of eligible people are fully vaccinated, and 67% are boosted, compared with 69% of those eligible vaccinated and 50% boosted in the US.

"What we see happening in the UK is going to be perhaps a better story than what we should be expecting here," Althoff said.

In the Netherlands, it took about a month for BA.2 to overpower BA.1, she noted. If the same timeline occurs in the US, that will mean the variant is taking off just as the immunity generated by winter's Omicron infections will be waning.

"I'm concerned about that," Althoff said. "But we were in a similar situation last spring, where we really got hopeful that things were going to settle down, and we got a little bit of a summer, and then we got walloped by Delta."

It will be important for people to understand they may be able to take their masks off for a few weeks, Althoff said, but they might also need to go back to wearing them regularly if cases spike.

"We could see another wave of illness at our hospitals," she said.

Althoff will also be closely watching wastewater data over the next few weeks.

"Wastewater surveillance is an incredible advancement in how we can monitor SARS-CoV-2 and what it's doing in the population without needing, really, any input from people," she said. "Keeping our eye on wastewater surveillance is an important tool to understand where the virus is going and if it's increasing in terms of infection."

Preparing for the next wave

Protection against the next variant has to start with vaccination.

"We absolutely have to continue to find people who are unvaccinated and get them vaccinated," Althoff said.

Fauci agreed that vaccination rates could be better in all age groups but said current numbers are especially bad for kids. Data collected by the CDC show about 28% of children ages 5 to 11 are fully vaccinated, while 58% of kids ages 12 to 17 have had two doses of a Covid-19 vaccine.

Even though the youngest children, those under 5, can't yet be vaccinated, recent studies have shown young kids are less likely to catch Covid-19 when they're surrounded by vaccinated older children and adults.

"So the way you protect them is to surround the children, to the extent possible, with people who are vaccinated and boosted so that you have somewhat a veil of protection around them," Fauci said.

It will also be important to continue to be flexible.

"The important thing in this massive experiment where we're dropping all masking and restrictions is we have to stay diligent in terms of monitoring of it and testing and be prepared to possibly reverse a lot of the relaxing of these restrictions," said Deborah Fuller, a microbiologist at the University of Washington.

"We can't let our guard down, because the message that people get when they say 'we're lifting restrictions' is the pandemic is over. And it's not," she said.

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