American biotech firm Moderna, Inc. says its vaccine remains effective against mutations but that it will continue to develop boosters for variants.

Some scientists say a South Africa mutation can evade antibodies generated by some COVID-19 treatments. The South African variant might also reduce the efficacy of the current line of available vaccines, including Moderna's, the experts say.

Moderna's vaccine remains effective against the variant detected in the UK in September, the company says. The mutation is reported to be 70% more transmissible than the dominant strain. It is not thought to be more lethal, however.

Moderna said it tested the feasibility of adding a second booster - taking total inoculations per individual to three shots. It said it had already begun preclinical studies on a booster specifically for the South African variant after tests showed the vaccine might produce a diminished antibody response after contact with the variant.

Moderna said the two-dose regimen of the vaccine was still expected to be protective against the South African and other variants detected to date. But it will push ahead with developing a new booster out of caution. The current inoculation regimen is for two shots, four weeks apart.

"We are encouraged by these new data, which reinforce our confidence that the Moderna COVID-19 Vaccine should be protective against these newly detected variants," said Moderna chief executive Stephane Bancel.

"Out of an abundance of caution and leveraging the flexibility of our platform, we are advancing an emerging variant booster candidate against the variant first identified in the Republic of South Africa into the clinic."

Bancel said the antibodies produced by the variant "remain above levels that are expected to be protective."

Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, said new data showed vaccines appeared to be less effective against some of the new COVID-19 strains.

Fauci said even if drugs and vaccines were less effective against more transmissible strains they would still likely provide enough protection to make them worthwhile.

A dip in effectiveness is "all the more reason why we should be vaccinating as many people as you possibly can," Fauci said.

The European Center for Disease Prevention and Control said the South African mutation and other variants "are considered to be of concern because of mutations which have led to increased transmissibility and deteriorating epidemiological situations in the areas where they have recently become established."

British Prime Minister Boris Johnson said there is "some evidence" the variant first identified in the UK might be deadlier than the original strain.

"We've been informed that in addition to spreading more quickly, it also now appears that there is some evidence that the new variant-the variant that was first discovered...may be associated with a higher degree of mortality," Johnson said.