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As concerns intensify over variants of the COVID-19 virus, the U.S. has solid grounds for thinking it might escape the full fury of the most frightening variants. Luck is a large part of the reason.

Variants, which arise inevitably as a virus spreads, have become a major concern as more are discovered and prove to be more transmissible and more lethal than the original COVID-19 virus. Variants discovered in the U.K., South Africa, and Brazil have already circled the globe. Others have emerged in New York and California; new research finds that the California variant now accounts for most of the cases in 44 counties there.

Especially worrying in the U.S. is the possibility of repeating Britain’s harrowing January experience, when COVID cases overwhelmed hospitals and some patients had to be moved to hotels. But William Hanage, an associate professor of epidemiology at the Harvard T.H. Chan School of Public Health, says the U.S. may well avoid that scenario, for a few reasons.

The U.K. variant struck that country at the worst possible time of year, which is now past. “Regular seasonal coronaviruses peak in January,” Hanage told journalists on a call.

The U.K. variant didn’t begin spreading rapidly in the U.S. until February, which “may mean that the point at which [this] variant is becoming locally common [in the U.S.] is the part of the year where it doesn’t transmit quite as well.” As a result, he says, “I do think that we are going to be entering this at a better time.” Other variants have arrived even more recently.

In addition, millions more people have been vaccinated than had been vaccinated in January, and the vaccines appear to be at least somewhat effective against the variants—in fact more effective than previously believed, according to new data. Galit Alter, a professor at Harvard Medical School, reports that the variants “don’t seem to affect T cell immunity all that much,” and T cells attack infected cells. As a result, she says, vaccines “will continue to provide protection against these newly emerging variants.”

A related factor, Hanage says, is that “in some parts of the country where there has been a lot of disease, it may be the case that infection-acquired immunity is playing into [the seasonality effect].” Increasing immunity is an important factor in the dramatic decline in new cases generally, he believes, and will dampen the spread of variants.

And people do respond to changing conditions. “When there’s a very large number of deaths, [people] change their behavior, and they make different contact patterns,” Hanage says. It’s another reason new cases are declining and a reason to think variants may be less damaging than if they had arrived earlier.

Hanage emphasizes that he isn’t minimizing the variant threat: “There’s every reason to be intensely concerned about the variants.” The effects will vary across the country, with a particular concern being Florida, where the U.K. variant seems to be well established, and the public health response has not been “hugely active.”

But his big-picture view of the devastating U.K. variant’s effect on the U.S. offers at least a welcome bit of hope: “I don’t think there is going to be a definitive national surge, at least not in the next few months.”