COVID-19 Vaccines: Reduced Activity Against B.1.351 Strain / Delaying Second Dose?

By Christine Judge

Edited by André Sofair, MD, MPH, and William E. Chavey, MD, MS

The Pfizer-BioNTech and Moderna COVID-19 vaccines show reduced effectiveness in neutralizing the highly transmissible SARS-CoV-2 variant B.1.351 that was first identified in South Africa, according to serum analyses published in the New England Journal of Medicine.

Industry researchers tested the serum neutralizing ability of their vaccines against engineered versions of SARS-CoV-2 from the reference strain (D614G), the B.1.1.7 variant first found in the U.K. (Moderna only), and B.1.351, using blood samples from vaccine trials.

Both studies showed reduced neutralization of B.1.351; serum from the Pfizer-BioNTech group had two-thirds reduced neutralization of B.1.351, compared with the reference viral strain. The authors of this paper concluded: "It is unclear what effect a reduction in neutralization by approximately two thirds would have on [vaccine]-elicited protection from [COVID]-19 caused by the B.1.351 lineage of SARS-CoV-2."

The Moderna analyses found that serum neutralization of the B.1.1.7 variant was not significantly reduced.

In other COVID-19 vaccine news, a pair of Canadian researchers urge delay of the second dose of mRNA vaccine in favor of providing a first dose to high-risk groups in the case of supply shortages. In a New England Journal of Medicine correspondence, they provide supporting data analyzed from documents submitted to the FDA showing extremely high efficacy of the Pfizer-BioNTech vaccine beginning 2 weeks after the first dose up until the time of the second dose (93%). Little protection is added in the short term from receiving the second dose within 1 month of the first.