Results from in vitro neutralization studies of sera from individuals vaccinated with Moderna’s coronavirus disease 2019 (COVID-19) vaccine, mRNA-1273, showed that vaccination produced neutralizing titers against all key emerging variants tested, including those identified in the UK (B.1.1.7 variant) and the Republic of South Africa (B.1.351 variant).

The study, which was conducted in collaboration with the Vaccine Research Center at the National Institute of Allergy and Infectious Diseases, showed no significant impact on neutralizing titers against the B.1.1.7 variant relative to prior variants. While a 6-fold reduction in pseudovirus neutralizing antibody titers was observed with the B.1.351 variant, it is expected that the levels of neutralizing antibodies would still be protective, according to Moderna.

“We are encouraged by these new data, which reinforce our confidence that the Moderna COVID-19 vaccine should be protective against these newly detected variants,” said Stéphane Bancel, Chief Executive Officer of Moderna. “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.”

In the US, a phase 1 study will evaluate mRNA-1273.351, an emerging variant booster candidate against the B.1.351 variant. The Company will also test whether an additional booster dose of mRNA-1273 (beyond the current 2-dose regimen) has the ability to increase neutralizing titers against emerging strains.

Under the Food and Drug Administration’s Emergency Use Authorization, the mRNA-1273 vaccine is authorized for active immunization to prevent COVID-19 disease in individuals 18 years of age and older.


Moderna COVID-19 vaccine retains neutralizing activity against emerging variants first identified in the UK and the Republic of South Africa. [press release]. Cambridge, MA: Moderna; January 25, 2021.