England has begun house-by-house COVID-19 testing in some communities as authorities try to snuff out a new variant of the coronavirus before it spreads widely and undermines a nationwide vaccination program.

Authorities want to reach the 80,000 residents of eight areas where the variant, first identified in South Africa, is known to be spreading because a handful of cases have been detected among people who have had no contact with the country or anyone who traveled there.

Officials are dispatching home testing kits and mobile testing units in an effort to reach every resident of those communities. It is “critical” for everyone in these areas to stay at home unless travel is absolutely essential, Health Secretary Matt Hancock said.

“Our mission must be to stop its spread altogether and break those chains of transmission,” Hancock told the House of Commons on Tuesday.

Public health officials are concerned about the variant first identified in South Africa because it contains a mutation of the virus’ characteristic spike protein that existing vaccines target. The mutation may mean the vaccines offer less protection against the variant.

As the door-to-door testing drive got underway, Public Health England also said scientists had discovered the same spike protein mutation in 11 cases involving another variant that is now the most prevalent form of the virus in England. The mutation had not previously been detected in the so-called Kent variant, named for the English county where it was first identified.

Britain’s government announced in December that the country had to introduce tougher restrictions to control the rapid spread of the Kent variant, which first was discovered a few months earlier in southeast England. Authorities were alarmed by how fast it spread, saying it was more contagious than existing coronavirus variants.

No conclusive evidence has emerged to show the Kent variant causes more serious COVID-19 cases or deaths. Dozens of nations around the world imposed bans on travel from the U.K. as cases multiplied in England, but the variant nevertheless has turned up in numerous countries.

While viruses mutate constantly, most of the changes cause little concern. But scientists are closely tracking mutations in the virus that causes COVID-19 to make sure they quickly identify variants of concern.

Dr. Julian Tang, a clinical virologist at the University of Leicester, said the recent discovery of the spike protein mutation in the Kent variant was a “worrying development, though not entirely unexpected.”

“Closing borders/restricting travel may help a little with this, but there is now probably already a sufficient critical mass of virus-infected people within the endemic U.K. population to allow this natural selection/evolution to proceed — as this report suggests — so we really need to stick to the COVID-19 lockdown restrictions as much as possible,” Tang said in a written statement.

In recent weeks, scientists also identified new, more contagious variants in South Africa and Brazil, both of which contained the spike protein mutation.

In hopes of preventing those variants from becoming widespread in Britain, the government has barred travel from South Africa, South America and Portugal, a popular European transit point for travelers from South America.

The discovery that the variant from South Africa is spreading in the community has led to calls to shut the U.K.’s borders to all international travelers or to require a 14-day hotel quarantine for everyone entering the country.

But closing the borders isn’t sustainable, said Professor Andrew Hayward, a professor of infectious disease epidemiology at University College London.

“You can think about completely shutting the borders or having quarantine, (but) what’s the end game in that?” Hayward told Sky News. “Is that something that you’re going to do forever, because it looks like these strains may continue to arise in the long term? So we need some sort of sustainable strategy, and I think that’s very difficult for politicians to think about that.”

(AP)