By Miriam Berger

Scientists had already determined that the variant of the novel coronavirus first detected in the fall in the United Kingdom — known as B.1.1.7. because of its molecular makeup — was probably 30 to 70 percent more transmissible than the typical version of the virus causing covid-19.

They also knew, based on preliminary data, that the variant appeared to be relatively more deadly for the growing number of people catching it.

U.K. scientists now say the variant is probably 30 to 70 percent more deadly, based on a follow-up study by the government released Friday that assessed a larger sample size of covid-19 patients and also found a higher rate of hospitalization.

The variant is “associated with an increased risk of hospitalization and death compared to infection with” other forms of the virus, according to the study, which drew from multiple databases across the country.

There are still many unknowns: The data available to study has noteworthy gaps among critical demographics, such as nursing homes, and provides an incomplete tally of infections, a problem that has persisted throughout the pandemic. But it does underscore how — even with efforts to fast-track fighting the virus — scientific data takes time to gather and access, despite the pressing need for information.

In the months since the variant was first reported — and the weeks since British Prime Minister Boris Johnson initially said it appeared to be deadlier — the highly transmissible form of the virus has spread to more than 80 countries, including the United States, and become the dominant strain in some parts of Britain. It has led to overwhelmed hospitals, disrupted travel and business, and necessitated a return to lockdowns in cities across Europe, even as coronavirus vaccination programs roll out to inoculate millions of people. Scientists sequencing the virus have also detected several other highly transmissible variants, such as one that was first documented in South Africa.

The rapid spread of variants led Britain in January to institute a comparatively longer and stricter lockdown than the country’s previous ones. Other countries in Europe that first reported surges in cases this winter have recently seen declines in their rates of transmission after prolonged shutdowns were put in place to prevent further spread of the B.1.1.7 variant.

Alongside lockdowns, some countries in Europe have also increased their face-mask requirements and recommendations in response to initial reports about the threat of the variants. On Wednesday, the U.S. Centers for Disease Control and Prevention issued new guidelines urging people to wear two cloth masks or medical-grade masks, when available, to limit the chance of spreading or contracting the various forms of the virus in circulation.

So far, the makers of the Moderna and Pfizer-BioNTech coronavirus vaccines have said their products remain effective against the latest forms of the virus. Studies of these variants and the various vaccines under development or emergency use are ongoing.