NEWARK — Travelers coming into New Jersey on flights originating in the United Kingdom will have to prove that they have tested negative for the coronavirus.

The policy announced Christmas Eve by Gov. Phil Murphy and United Airlines, which operates out of Newark Liberty International Airport, comes after troubling discoveries of mutant strains of the coronavirus in Britain, South African and Nigeria.

The policy by United begins Dec. 28. It requires that their customers traveling from from London Heathrow to Chicago, Newark, Washington Dulles and San Francisco provide proof of a negative COVID-19 PCR, LAMP or antigen test taken within 72 hours of their departure. Rapid tests also will be available at the London airport.

The policy applies to all fliers over the age of 5. Passengers from other countries who connect with a United flight from London would be exempt.

Murphy and public health officials have been encouraging people not to travel at all for the holidays.

"As we continue to experience a second wave of COVID-19 cases, it’s critical that we take any and all precautions to mitigate the potential for further transmission," Murphy said in a written statement on Thursday.

In a written statement provided by Murphy's office, the airline said it "has been a leader in enacting new policies and innovations designed to keep employees and passengers safer when traveling including mask mandates and requiring customers to complete a 'Ready-to-Fly' checklist before the flight acknowledging they have not been diagnosed with COVID-19 in the last 14 days and do not have COVID-related symptoms."

David Kennedy, an evolutionary microbiologist at Penn State, said the mutation seen in Britain was concerning because research so far suggests the new strain is "more transmissible than the original virus," making it "more dangerous in the sense that it will make more people sick."

While more research is needed, scientists believe the coronavirus vaccines would still be somewhat effective against the new strain by limiting the severity of COVID-19.

The Associated Press contributed to this report.

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