The new variants have created some concern that mutations in the virus may make the vaccines less effective.

The company said it found no reduction in the antibody response against the variant found in Britain, but the South Africa variant caused a reduced response.

Madonna is testing a third booster shot, to be sure, but says it's two doses provide protection for at least a year.

Dr.

Peter Hotez, dean of the National School of Tropical Medicine at Baylor College, said he was only mildly concerned that the vaccine wouldn't be protective because the level of virus neutralizing antibodies still quite high that's six fold reduction should not interfere with protection, although potentially it could cause a slight reduction.

Madonna said the new booster shot could be made available in the future if evidence were to emerge.

That protection declined.

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

The variant was first seen in Britain in September and caused a massive surge in cases there and elsewhere.

It's being found in more than a dozen U.

S states and is expected to be the dominant variant there within six weeks.