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What’s fueling Omicron to become more transmissible? How human behavior factors into the spread of variant BA.2.12.1

What’s fueling Omicron to become so much more transmissible? And what is the best approach to testing amid all this uncertainty?Barry Chin/Globe Staff/file

It didn’t seem that long ago that infectious disease experts spoke hopefully of a spring reprieve in COVID-19 cases. But that was before the latest, even more, transmissible Omicron variant, BA.2.12.1, exploded across Massachusetts in recent weeks and began to shove aside its predecessor, BA.2, in other regions, as well. Cases are climbing, edging the United States across the threshold of 1 million deaths. Hospitalizations are rising too, albeit more slowly.

The levels of coronavirus detected in Eastern Massachusetts waste water — a bellwether for future infections — also continues a march upward. The virus seems relentless, as fully vaccinated and boosted people who managed to escape it are reporting infections.

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So what’s fueling Omicron to become so much more transmissible? And what is the best approach to testing amid all this uncertainty?

Is the virus mutating faster now?

Probably not, said Dr. Jeremy Luban, a molecular and biochemistry professor at the UMass Chan Medical School who has spent years studying viruses. “I have not seen any evidence that it has a higher mutation rate due to some intrinsic property of the virus,” said Luban, codirector of the Massachusetts Consortium on Pathogen Readiness. As more people have gained some sort of immunity through vaccination, infection, or a combination of the two, the virus is under more pressure to keep changing slightly, by finding weak spots to evade detection by antibodies, the gatekeepers in the immune system. Earlier versions of the virus, such as Alpha, the dominant variant that produced the USsurge in the winter of 2020/2021, also spit out a number of subvariants, Luban said. But few became household names because they didn’t gain a foothold the way several Omicron subvariants have.

It’s not that the virus has mutated so much in its basic structure since its original strain, but people’s behavior has, giving later variants an opportunity to gain traction, Luban said. “It may have a lot more to do with the fact that people were locked down with Alpha and now people are flying all over the planet,” he said. “Things are totally different now in terms of human behavior.”

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Can at-home rapid antigen tests detect this new variant?

Yes. But, as is the case with earlier variants, antigen tests may not show a positive result until a few days after you’ve contracted COVID-19.

“The antigen tests are really good at turning positive when you are infectious,” said Dr. Jennifer Nuzzo, a professor of epidemiology at Brown University School of Public Health. “But they tell you your status at that moment, so that’s why [if you have symptoms] you can’t assume a negative test means you are in the clear. You can wake up the next morning, or several hours later, and you can test positive.”

PCR nasal swabs submitted for processing in a lab are more sensitive than at-home antigen tests and are more likely to show a positive result earlier in the infection. Nuzzo said a negative home antigen test may just mean a person’s viral load is not yet high enough to be detected.

Someone exposed to a person with COVID should assume they are positive and take precautions around others until they know for sure they were not infected. Nuzzo and other experts suggest people repeat antigen tests up to three and even four days after an exposure.

“If I had lots of symptoms and yet had a negative PCR test, I would draw more confidence in that,” Nuzzo said. “But I would draw less confidence in a rapid antigen test [if I had symptoms]. There is a low likelihood I am infectious, but I don’t know about an hour or two later.”

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What about at-home PCR-like tests?

Known as LAMP tests, they amplify pieces of the virus’s genetic material, known as RNA, to detect infection. The process is similar to PCR tests, only LAMP tests rely on enzymes instead of heat to do the amplification.

“Lamp tests are more sensitive than antigen tests,” said Dr. Michael Mina, an epidemiologist and chief science officer at eMed, a telehealth company. But the difference in sensitivity is not great. LAMP tests may be able to detect positive cases about 8 to 12 hours earlier than at-home rapid antigen tests, he said.

From the pandemic’s early days, Mina championed at-home antigen tests to speed up access because lab-based tests often took days to report results. Now, antigen tests are widely available at most pharmacies and cost about $25 for a kit of two tests. But LAMP tests run about $75 for a single test. Many people can’t afford to perform multiple at-home LAMP tests, or their insurance doesn’t cover it, making them not practical for most people, Mina said.

But wait. Aren’t there free COVID tests and masks?

Yes, every home is eligible to order a third round of free at-home tests from the Centers for Disease Control and Prevention. These are antigen tests. (Order online or call 1-800-232-0233.) Also, the government has shipped N95 masks to many pharmacies that provide them free to customers, although few advertise the supply. (Find a participating pharmacy near you online.)

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Are the gold-standard PCR lab tests still available?

Absolutely. The Massachusetts Executive Office of Health and Human Services website allows users to search for locations nearby, simply by typing in their ZIP code. Some locations still offer the tests free, but appointments are typically required. Also, people who don’t have access to a computer can dial the state’s free COVID help line at 2-1-1 for assistance.

Additionally, some cities, including Cambridge and Somerville, offer free tests for residents so check the website of your city or town.

And for those seeking treatment for COVID, a state website provides information and available free options: https://www.mass.gov/info-details/treatments-for-covid-19



Kay Lazar can be reached at kay.lazar@globe.com Follow her on Twitter @GlobeKayLazar.