The COVID-19 pandemic is not an on-off switch
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During the winter surge of COVID-19, it felt like the coronavirus was everywhere. Colder weather pushed people inside where the virus can linger in the air, and the surge-dominating omicron variant of SARS-CoV-2, the virus that causes COVID-19, had the troublesome ability to dodge some immune responses (SN: 5/18/21). That meant that both vaccinated or previously infected people were more susceptible to getting infected than they were with previous coronavirus variants. Perhaps that shouldn’t have been a surprise given the vaccines’ primary goal is to prevent severe disease and death (not to prevent infection at all, what’s called sterilizing immunity). Still, omicron caught everyone off guard.
Finally, weeks after COVID-19 cases skyrocketed, they continue to trend downward in most parts of the United States and around the world. Every time cases drop, I find myself holding my breath, hoping that signs of a resurgence won’t appear. So far, so good — for now. I might be able to let that breath out soon, for at least a bit. (Although cases in New Jersey, where I live, appear to be plateauing at levels close to the peak of last summer’s delta wave.)
The bulk of the winter COVID-19 cases were caused a subvariant of omicron dubbed BA.1. Researchers are now keeping an eye on its close sibling, an omicron subvariant called BA.2. Even as cases decrease overall, BA.2 is on the rise, accounting for an estimated 4 percent of new cases in the United States for the week ending February 19.
BA.2 concerns researchers because it is slightly more transmissible than BA.1, which could extend the current surge, and it also has some different mutations than BA.1. Both BA.1 and BA.2 can evade immune responses by dodging virus-attacking antibodies sparked by vaccination or infection with other variants, and some of BA.2’s differences might mean it could evade antibodies made after a BA.1 infection (SN: 12/21/21). So far, that’s not what scientists are seeing. Instead, even though these types of reinfections can happen, they are rare, a team from Europe reports in a preliminary study posted February 22 at medRxiv.org. Reinfections with BA.2, the team found, were most common in young, unvaccinated people who weren’t hospitalized. Time will tell how long this protection holds up and how it might fare against future variants or subvariants.
This isn’t the first time we’ve worried about reinfections. An eon ago in pandemic time, in early 2021, the emergence of the alpha, beta and gamma variants sparked concerns that more people might soon be faced with a second bout of COVID-19. So in February of last year, I interviewed epidemiologist Aubree Gordon of the University of Michigan in Ann Arbor to hear her thoughts on what variants might mean for the pandemic at large (SN: 2/5/21).
Back then, our understanding of reinfections was in its infancy. Studies hinted that the beta and gamma variants could evade parts of the immune system, making reinfections possible. But we didn’t know how common reinfections were or if a second bout of COVID-19 might be less severe than the first. Meanwhile, the vaccine rollout in the United States was inching along, with many people desperately seeking first doses. Last year, Gordon, who has been studying coronavirus reinfections, told me that the new variants might prolong the pandemic. But she was quick to remind me that even in the face of variants, pandemics always end.