Close to half of recent COVID-19 cases in Pennsylvania and New Jersey are due to infection with a more transmissible coronavirus variant first identified in Britain, according to data from one testing company.

And the total number of cases continues to climb in both states.

So the variant must be to blame, right?

Only somewhat, says Michael LeVasseur, an assistant professor of epidemiology at Drexel University’s Dornsife School of Public Health. Likely much, even most, of the recent rise in cases is driven by people relaxing precautions before most are fully vaccinated, he said.

“People want to have Party City USA,” he said. “They’re sort of jumping right in, and that’s not how this should work.”

It is tricky to sort out exactly how much of the recent rise in cases is caused by increased infectiousness of the virus and how much is due to the behavior of its human hosts, as the two phenomena are intertwined. One way to answer the question would be to compare how fast case numbers are rising now with the rate during previous upswings, he said.

But the underlying truth of infectious-disease epidemiology is that human behavior plays a prime role in any trend. And now that the vaccines are becoming available to larger numbers of people, this is no time to abandon all precautions, LeVasseur said.

“Continue doing the things we’ve been saying to do from the start,” he said.

The numbers on the variant come from Helix, a genetic testing company in San Mateo, Calif., that tracks the trends in two ways. One involves deciphering the complete 30,000-letter code of the coronavirus, a time-consuming approach that generally means the results are not compiled until several weeks after testing.

A faster, shorthand method for identifying the variant involves using the regular PCR tests of patient nasal swabs. Individuals are said to test positive if their swabs contain genetic material from three telltale regions of the viral genome.

But the signature mutation of the “British” variant, formally called B.1.1.7, happens to fall in one of those three telltale regions — meaning that a sample from an infected person will come back as positive for just two regions, rather than all three. This test by omission — the “S-Gene Target Failure,” abbreviated SGTF — is widely accepted as evidence that the variant is present.

» READ MORE: Variants vs. the vaccines: a race against time?

For the week that ended March 28, the variant accounted for 46% of new infections that Helix sampled in Pennsylvania. Likewise in New Jersey, the corresponding percentage recently has been in the 40s, though the company has less testing data for that state.

And in both states, several other variants of concern have been on the rise, though those data are delayed because there is no shorthand test yet for those variants. Labs must decipher the full genetic code in a patient sample.

Fortunately, the numbers of COVID-related deaths remain stable in both states and nationwide, according to Covid Act Now, a nonprofit that tracks pandemic trends. But the numbers of cases and hospitalizations are creeping upward, and in the past, deaths have gone up within weeks of hospital admissions rising.

Pennsylvania, New Jersey, and Connecticut are seeing some of the nation’s steepest increases in cases, according to a New York Times analysis. In terms of hospitalizations, another hot spot is Michigan, where the number of patients admitted with COVID-19 is more than triple what it was a month ago, the Times found.

And in Pennsylvania, there is another troubling data point: The percentage of tests that were positive for the coronavirus has risen sharply in the last three weeks, from 5.7% on March 11 to 9.4% on April 1. Higher rates, experts say, suggest that community spread is expanding.

So make an appointment to get vaccinated as soon as you are eligible, LeVasseur says, as evidence suggests that despite the various mutations, the vaccines remain potent in preventing severe disease. And for the time being, take it easy with any thoughts of Party City USA.