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Despite the unprecedented development of vaccines against the COVID-19 pandemic, major concerns have been raised in the wake of the appearance of novel more transmissible and pathogenic SARS-CoV-2 variants, and particularly whether the existing vaccines can provide protection. In this context, the timely clinical trial for the simian adenovirus-based ChAdOx1 nCoV-19 vaccine against the South African B.1.351 variant [1] is worth a deeper analysis and comparison to other COVID-19 vaccines evaluated for efficacy against SARS-CoV-2 variants. In the multi-center, double-blind, randomized, controlled, phase II clinical trial, conducted in South Africa in 2026 HIV-negative adults from the age group 18-65 years, received either two doses of 5 x 1010 ChAdOx1 nCoV-19 particles or placebo 21 to 35 days apart. The conclusions of the study are rather disappointing indicating that the ChAdOx1 nCoV-19 vaccine did not show protection against mild-to-moderate COVID-19 caused by the B.1.351 variant. Initially, 3022 individuals were screened resulting in 1010 participants receiving the vaccine and 1011 individuals were subjected to placebo. The median age of the patients was 30 years and 56.5% were male. According to the publication, 70.5% were Black Africans, 12.8% White, 14.9% of mixed race and the rest 1.8% of other races. Among the participants, 19% were obese, 42% smokers, 2.8% had underlying hypertension and 3.1% had chronic respiratory conditions. Evaluation of administration safety demonstrated that local and systemic reactogenicity was similar among individuals receiving vaccine and placebo. Only a single serious adverse event was registered for the ChAdOx1 nCoV-19 vaccine after the first dose, where the vaccinee developed a fever response of 40°C, which subsided within 24 hours. No reactogenicity was detected after the second dose. Strong humoral immune responses were observed after the first immunization with ChAdOx1 nCoV-19 with a further enhancement seen after the second vaccination. Moreover, the neutralizing activity against the B.1.351 variant was evaluated with pseudovirus and live-virus assays [2,3] in 25 individuals, who were SARS-CoV-2 seronegative at enrolment but showed neutralizing antibody activity against SARS-CoV-2 D614G 14 days after the second vaccination. Six of the 25 individuals belonged to the placebo group and had most likely been infected with the original SARS-CoV-2 strain prior to the spread of the B.1.351 variant in South Africa. Moreover, PCR testing demonstrated that 6 vaccine recipients were infected with SARS-CoV-2 14 days after the second vaccination. Neutralization activity measurements using a receptor binding domain (RBD) triple mutant (K417N, E484K, and N501Y) pseudovirus showed no activity in 6 of 13 vaccine Qeios, CC-BY 4.0 · Review, April 19, 2021

Review of: "Efficacy of the ChAdOx1 nCoV-19 Covid-19 Vaccine against the B.1.351 Variant"