Moderna (MRNA -1.75%) announced evidence that its COVID-19 vaccine is protective against all variants of the SARS-CoV-2 virus detected to date, including two strains first detected in the United Kingdom and South Africa. The level of protective antibodies against the U.K. strain, B.1.1.7, was equivalent to those against earlier variants. But while the antibodies to B.1.351, the South African strain, were believed to be sufficient to be protective against the disease, they were reduced, leading the company to move ahead with testing a new version of the vaccine aimed at that variant.

Vaccine being drawn into a syringe.

Image source: Getty Images.

Moderna's study was conducted in the laboratory by exposing blood serum from eight clinical trial participants aged 18 to 55 who had received the two-dose regimen of its mRNA-1273 vaccine and from two nonhuman primates to all key emerging variants of SARS-CoV-2. The level of neutralizing antibodies to all the variants were judged to be protective, but antibodies to the South African variant were reduced six-fold compared with the response to earlier variants.

Moderna CEO Stephane Bancel said, "Out of an abundance of caution and leveraging the flexibility of our mRNA platform, we are advancing an emerging variant booster candidate against the variant first identified in the Republic of South Africa into the clinic to determine if it will be more effective to boost titers against this and potentially future variants." The biotech company expects the booster could be given in combination with any of the leading vaccine candidates.

The new booster vaccine candidate, dubbed mRNA-1273.351, will be advanced into a preclinical study and a phase 1 trial in the U.S. Moderna will also test the effectiveness of a third dose of its standard vaccine as a booster against emerging strains of COVID-19.