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SARS-CoV-2 variants may compromise the effectiveness of vaccines, raising critical concerns. In an additional analysis of their randomized, controlled trials of the Oxford/AstraZeneca vaccine (ChAdOX1 nCoV-19; NEJM JW Infect Dis Feb 2021 and Lancet 2020 Dec 8; [e-pub]), U.K. investigators have evaluated the neutralization activity and efficacy of the vaccine against the B.1.1.7 variant.
Of 8534 trial participants, 520 developed SARS-CoV-2 infection. Among vaccine recipients, neutralizing antibody titers were about ninefold lower against the B.1.1.7 variant than against an earlier lineage. Despite this reduction in laboratory-based neutralization, vaccine efficacy against symptomatic infection was 70.4% (B.1.1.7 variant) and 81.5% (non-B.1.1.7 lineages). Among those with symptomatic or asymptomatic infection, SARS-CoV-2 levels were lower and duration of PCR positivity shorter in the vaccine group than the control group. The number of positive weekly swabs was the same in participants who had B.1.1.7 and non-B.1.1.7 infection.
Emary KRW et al. Efficacy of ChAdOx1 nCoV-19 (AZD1222) vaccine against SARS-CoV-2 variant of concern 202012/01 (B.1.1.7): An exploratory analysis of a randomised controlled trial. Lancet 2021 Apr 10; 397:1351. (https://doi.org/10.1016/S0140-6736(21)00628-0)
Comment
These findings provide reassurance that, despite a drop-off in neutralizing antibody titers, the ChAdOX1 nCoV-19 vaccine continues to protect people from infection by the B.1.1.7 variant. What explains these apparent inconsistencies? Vaccine-elicited antibody levels may be high enough to protect against infection, or other immune responses (e.g., T cells) may ameliorate symptoms even if infection occurs. Variants that are more difficult to neutralize — such as B.1.351 — might be a different story: The ChAdOX1 nCoV-19 vaccine did not protect against mild-to-moderate infection with this variant in a study in South Africa (N Engl J Med 2021 Mar 16; [e-pub]). Clearly, the particulars of the specific vaccine and the variants both matter as we accelerate efforts to contain the pandemic.