In this Dec. 2, 2021, file photo, a passer-by enters a pharmacy with a vaccination advisory attached to a door, right, in Worcester, Massachusetts. Credit: Steven Senne / AP

PITTSBURGH — A subvariant of omicron is now driving a surge in COVID-19 cases in the United Kingdom, Europe and parts of Asia, but in Western Pennsylvania, health experts don’t foresee another dramatic wave of infections.

The subvariant, known as BA.2, isn’t new; it first emerged in November and has been circulating in Pennsylvania and the rest of the United States for more than two months. At a time when overall coronavirus cases are declining across the country, the prevalence of BA.2 has doubled over the past two weeks. The subvariant now makes up about 35 percent of cases nationwide, according to the Centers for Disease Control and Prevention.

Scientists have been keeping an eye on BA.2 because it’s even more contagious than the original omicron strain, known as BA.1, which was responsible for record-high case counts, hospitalizations and deaths in early January. The BA.2 subvariant does not seem to cause more severe disease than its parent strain.

“The bottom line is, we’ll likely see an uptick in cases, as we’ve seen in the European countries, particularly the U.K.,” White House chief medical adviser Dr. Anthony Fauci told ABC’s “This Week” earlier this month. “Hopefully we won’t see a surge — I don’t think we will.”

State health authorities in Pennsylvania are also hopeful that cases will remain low for a while, and they are not anticipating more hospitalizations or deaths due to BA.2.

“While the department cannot rule out the possibility of a surge in cases due to BA.2, we are not anticipating a surge in cases comparable to the omicron surge in late 2021 and early 2022, and there is no evidence to suggest that hospitalizations or deaths would dramatically increase,” said Mark O’Neill, spokesman for the Pennsylvania Department of Health.

In Allegheny County, the health department reported that about 10 percent of COVID-19 cases during the week of March 13-19 were due to the BA.2 variant. The week before, BA.2 made up about 6% of cases. The county began testing a portion of positive cases for variants in January.

“The rate of increase of BA.2 seems to be slower here than it is elsewhere,” said Vaughn Cooper, a microbiologist at the University of Pittsburgh. “I’m cautiously optimistic that we’re not going to see a true surge, largely because its timing is coinciding with better weather and more outside time.”

That’s not the case in Europe, where BA.2 has been rising at a time when people are still mostly indoors because of the cold weather.

Locally, the proportion of cases caused by BA.2 is rising but that has yet to translate to an uptick in cases. In Allegheny County, there were 457 infections reported the week of March 13-19. The last time case counts were this low was the end of July of last year. Part of that could be because fewer people are seeking laboratory tests when they’re sick. More individuals are also using at-home tests and not reporting the results to health authorities.

“We may not see that surge, and if we do, it might not be for a few more weeks,” said Dr. Matthew Moffa, medical director of infection prevention at Allegheny Health Network’s West Penn Hospital.

To know whether the region is in for another spike in cases, local health officials are keeping an eye on sewage — the amount of coronavirus in sewage, that is. The virus can show up in stool samples before outward symptoms of infection do and thus end up at wastewater treatment plants before individuals decide to get tested for COVID-19. That makes wastewater a good predictive tool of how widespread the virus is within a community.

The county health department started testing sewage at a handful of wastewater treatment plants at the end of October. Testing involves determining the viral count, or concentration of virus in a sample of wastewater.

From the end of January until the beginning of March, wastewater data showed that the viral count was decreasing. But that trend reversed in early March, with viral counts rising slightly. Wastewater samples from the week of March 13-19 showed stable viral counts.

“Increasing viral counts in our wastewater data tends to be a harbinger of increasing case numbers,” Cooper said. If virus concentrations start increasing week over week, that would signal a coming rise in cases.

The good news is that the high number of omicron cases in Western Pennsylvania may help shield the area from a BA.2 spike. People recently infected with the original omicron variant probably had a good degree of protection against BA.2, especially if they were vaccinated.

A study in Denmark, where BA.2 hit early, found that people who were infected with BA.1 rarely get reinfected with BA.2 shortly afterward. The reinfections mostly affected young, unvaccinated individuals and did not cause hospitalizations or deaths. The results were posted online last month but have not been peer-reviewed.

Given BA.2’s increased transmissibility and the relaxation of masking and social distancing, those who haven’t been infected with COVID-19 yet and are still unvaccinated remain at risk, Cooper said.

COVID-19 vaccines are still effective against the BA.2 subvariant, so individuals who are up to date with their vaccinations should have strong protection against severe illness, hospitalization and death.

“Now is a great time for those who are not up to date with their vaccine regimen to do so, as vaccines are available for booster shots, as well as first and second doses,” O’Neill said.

Story by Emily Mullin, Pittsburgh Post-Gazette.