COVID-19 hospitalizations continue to rise in Mass.

BOSTON — By now, the cycle is familiar. As COVID-19 case numbers drop, so does the perceived need for caution. That gives the virus an opening it has, so far, never failed to exploit.

Sure enough, as masks came off and March drew to a close — case numbers in Massachusetts rose. The seven-day average positivity rate is up 40 percent in the last two weeks, according to the state Department of Public Health — rising from 1.9 percent on March 21 to 2.66 percent Wednesday.

But until this week, the number of those hospitalized with COVID continued to decline from a peak of more than 3,200 in mid-January. Over the past couple of days, DPH reports average hospitalizations rose from about 216 patients to 220.

“I think it is something we need to be watching carefully,” said Daniel Kuiritzkes, MD, chief of the Division of Infectious Diseases at Boston’s Brigham and Women’s Hospital. “There was all this excitement that cases were tumbling from the peak of Omicron. But they never got as low as we were in June a year ago when we were down at around 60 cases a day.”

In fact, Massachusetts cases over the last two weeks barely dipped below 600 before beginning a sustained climb.

“Whether that means we can expect another spike or whether this is just going to be a blip, we really can’t say until we see what happens over the next several weeks,” Kuritzkes said.

What’s unusual about the Omicron wave is that it is getting a second wind — in the form of a subvariant — BA.2 — thought to be more transmissible, even, than the highly contagious initial Omicron — BA.1.

“We are seeing the prevalence of BA.2 increasing as the overall Omicron wave has crashed,” said Jeremy Kamil, PhD, associate professor of Microbiology and Immunology at Louisiana State University in Shreveport. “It is spreading. It can infect people who were previously vaccinated, particularly if they didn’t have a case of BA1.”

But Kamil said there is good news, when it comes to the future extent of BA.2 spread.

“Most people who recovered from a BA.1 breakthrough infection, especially if they were vaccinated, are going to have really potent immunity against BA.2.”

Not certain immunity, Kamil said — and not permanent immunity — but certainly, when combined with vaccination, the kind of immunity that will likely prevent development of subsequent serious COVID illness.

But, Kamil cautions, vaccination remains key.

“People who are vaccinated recover faster, they get less ill and they spread less virus to others if they spread it at all,” he said.

It’s estimated about half the U.S. population became infected with Omicron this winter — but the true extent of the surge in Massachusetts is unknown.

“Because we have so much home testing going on, we don’t have as reliable information about the actual number of cases that are present in the state,” Kuritzkes said.

And it’s likely some infections are never spotted at all — particularly during winter and spring, when it might be easy to dismiss a mild case of COVID with the common cold or seasonal allergies.

Hospitalization data helps track not only the severity of circulating variants — but also the extent of infections. But, with so much home testing going on, wastewater data provides a clearer picture of the state of the pandemic in a given area. For the last two weeks, COVID RNA fragments have been rising in MWRA samples. They are now at a level comparable to early February.

What does this all mean?

“The pandemic might continue smoldering on,” said Kamil. “As it trends towards something that looks more like an endemic.”

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