Moderna said it believes its COVID-19 vaccine protects against new variants found in Britain and South Africa, although it will test a new booster shot aimed at the South African variant after concluding the antibody response could be diminished.

The company said in a news release it found no reduction in the antibody response against the variant found in Britain. Against the South African variant, it found a reduced response but still believed its two-dose regimen would provide protection.

The emergence of new variants in Britain, South Africa and Brazil has created some concern that mutations in the virus may make vaccines less effective.

Moderna said it is looking at whether a booster shot – either of its existing vaccine or of a new shot designed to protect against the South African variant – could be made available in future if evidence were to emerge that protection declined.

“The virus isn’t going to stand still,” Moderna President Stephen Hoge said on a conference call. “While the current strains appear to be well-protected by our COVID-19 … it’s important that we remain vigilant and develop potential tools and countermeasures that would allow us to continue to beat back the pandemic.”

Moderna said it expects its current vaccine will remain protective for at least a year after completing the two-dose course. It does not expect to test a third dose until at least six months after that course is finished.

Dr Paul Offit, an infectious disease expert at the University of Pennsylvania and a member of the US Food and Drug Administration’s vaccine advisory panel, said he was only mildly concerned the vaccine would not be protective against the variants.

“It is a little worrisome that you see a lesser neutralizing antibody response, but that doesn’t necessarily mean that you are unprotected,” he said, noting that even these lower levels may still be enough to protect against serious infections.

“The goal of this vaccine is to keep you out of the hospital and to keep you out of the morgue. If you get a symptomatic infection or mildly symptomatic infection that is not a burden to the healthcare system,” Offit said.

Pfizer and BioNTech have also said tests showed their vaccine is effective against the variant found in Britain, but have not yet disclosed results against the South African variant.