BOSTON -- A contagious mutation of the coronavirus is increasingly showing up in laboratory tests in Massachusetts, as public health experts warn that it could become the dominant strain.

Over the weekend, the state Department of Public Health reported at least 19 new cases of the new COVID-19 variant known as B.1.1.7., which brings the number of cases to 29 since the mutation was first detected last month.

A majority of cases reported so far have been in Worcester County, and patients ranged in ages from 4 to 70, according to the Health Department. Only four were related to travel, suggesting that most of the known cases were "community acquired."

To date, no cases of the mutated virus been reported in Essex County.

Health officials say the new variant, which was first reported in the United Kingdom, is more contagious than other strains and similar to mutations recently identified in South Africa and Brazil.

It underscores the need for people to get quickly vaccinated and to continue taking precautions, health officials warn.

"The best defense against a rapid rise in cases from variants of concern is to prevent the spread of COVID-19," the Health Department said in a statement.

Dr. David Hamer, a professor at Boston University's School of Public Health and School of Medicine, said the coronavirus is constantly mutating and it may only be a matter of time before those variants become vaccine-resistant.

"Hopefully with the first, full round of vaccinations we can get closer to some level of herd immunity and better control over the virus," he said. "But in the future, as we look to boosters for the vaccines, there will need to be modifications made so there is better coverage of the current strains."

Hamer said recent studies raise concerns that vaccines don't work as well against a mutation that first detected in South Africa.

More than 1,000 cases of the U.K. strain have been detected in at least 39 states and several countries. New Hampshire reported its first case last week.

The U.S. Centers for Disease Control and Prevention predicts the UK variant will become the dominant strain in the country by next month.

"We estimate that about 4% of disease in this country is related to B.1.1.7," Dr. Rochelle Walensky, director of the CDC, told CBS News on Sunday. "And we have projections that it may be the dominant strain by the end of March."

Walensky said pharmaceutical companies are testing new versions of COVID-19 vaccines that specifically target the coronavirus variants while federal researchers reviews data on people who have already received the vaccines to determine if they can get infected a second time.

"We're doing the science to scale up different vaccines in case we either need bivalent vaccines, that is a vaccine that has two different strains, or booster vaccines," she said.

Christian M. Wade covers the Massachusetts Statehouse for North of Boston Media Group’s newspapers and websites. Email him at cwade@cnhi.com.

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