Moderna's COVID-19 vaccine is effective against new variants of the virus that first appeared in the U.K. and in South Africa, the company announced on Monday.

Yes, but: The vaccine was as effective against the strain from U.K., but saw a six-fold reduction in antibodies against the South Africa variant. Even still, the neutralizing antibodies generated by the vaccine "remain above levels that are expected to be protective," according to the company.

What to watch: Moderna now says it is developing an additional booster dose against the South Africa strain, and another booster to fight other emerging strains. The results of Moderna's tests have not yet been peer-reviewed.