COVID-19 is surging again in Europe thanks to the BA.2 subvariant and is likely to spread to the US soon

• Coronavirus cases in Europe are rising again as the BA.2 subvariant of Omicron spreads.
• COVID-19 waves in Europe typically precede the US by a couple of weeks.

COVID-19 cases are on the rise again in Europe after a slump over the Christmas holiday period, and experts are raising the alarm about another wave coming to the US.

COVID-19 waves in Europe have tended to precede a rise in cases in the US, and experts have suggested this could be the case here as well.

The rise in cases, shown below, is thought to be the result of a combination of the spread of a more contagious subvariant of Omicron called BA.2 and the lifting of COVID-19 restrictions in many European countries in recent weeks, Eric Topol, a cardiologist and the director of the Scripps Institute, wrote in The Guardian.

As of March 21, BA.2 made up 82% of sequenced cases of COVID-19 in the UK, 54% in Germany, 48% in France, and 48% in Italy, the variant-tracking website CoVariants.org said.

COVID-19 hospitalization rates are also on the rise in France and the UK, though both governments said that more people were being admitted for other reasons and testing positive for COVID-19 while in the hospital.

These "incidental" COVID-19 cases in hospitals made up more than half of UK hospitalizations, The Sunday Times reported.

BA.2 cases rising in the US

The proportion of BA.2 cases has also been rising in the US.

The subvariant made up an estimated 23% of cases in the week of March 12, up from 13.7% the week before, the Centers for Disease Control and Prevention said.

States in the northeast have the heaviest burden, with the BA.2 subvariant making up almost 40% of cases there.

New reported COVID-19 cases in the US dropped to about a 28,000 seven-day average on March 18 — the lowest level since July 13 last year.

But it is possible that the actual number of COVID-19 cases is higher than the figures show, Myoung Cha, an executive from Carbon Health, said in a Twitter thread.

That's because more people are testing at home and not seeking care, he said. Some US states are also starting to close testing sites.

Wastewater surveillance suggests there may be more COVID-19 cases than are being reported. Some sites in the US reported over a 1,000% increase in the levels of genetic material from the coronavirus detected in sewage compared with 15 days earlier, as shown below.

The US could get a worse wave

Some experts warn that the US could get a worse BA.2 wave than Europe, with unboosted vulnerable and older people at more risk than those in Europe.

The uptake of booster vaccines has been poorer in the US: As of March 13, only one in three in the US population had received a third shot, compared to about 60% in the UK, Germany, and Denmark.

"This is a critical issue, because there is a substantial dropdown of protection, from 90-95% with a third shot to 75-80% without a booster, versus Omicron hospitalization and death," Topol, the cardiologist, said in The Guardian.

On Sunday, he tweeted a graphic of a new variant, writing: "Don't be surprised. Plan for it. Prepare against it."