Moderna says vaccine works against variants but will test a booster for South Africa strain

A vial of Moderna's COVID-19 vaccine.
Moderna says its COVID-19 vaccine protects against variants of the coronavirus.
(Gary Coronado / Los Angeles Times)

Moderna says its COVID-19 vaccine protects against worrisome emerging variants of the coronavirus, but it’s taking the precaution of testing a possible booster dose against the strain discovered in South Africa.

In Monday’s announcement, Moderna Chief Executive Stephane Bancel said the move was out of “an abundance of caution” after preliminary lab tests suggested its shot produced a weaker immune response to that variant.

Vaccine manufacturers have been testing their shots against mutated strains, including two that first emerged in Britain and South Africa. In a study conducted with the National Institutes of Health, Moderna used blood samples from eight vaccine recipients, and some immunized monkeys, in laboratory tests against the mutated viruses.


The vaccine was effective against both variants, but researchers found a sixfold drop in levels of “neutralizing antibodies” against the strain from South Africa. Moderna said while the levels still were protective, it has begun developing a booster vaccine targeted to that new strain, called the B.1.351 variant. In addition, Moderna will test if simply giving an extra dose of the original vaccine could be helpful.

Pfizer, which makes a similar COVID-19 vaccine, has previously reported that its shot also appears effective against the strain from Britain. But other research has raised questions about the variant from South Africa.