• Efficacy of the ChAdOx1 nCoV-19 Covid-19 Vaccine against the B.1.351 Variant | NEJM
    https://www.nejm.org/doi/full/10.1056/NEJMoa2102214

    L’inefficacité du #vaccin AstraZeneca contre les formes légères et modérées de #COVID-19 en rapport avec le #variant « sud-africain » de #SARS-CoV-2 semble se confirmer.

    Il n’y a pas eu de formes graves dans les deux groupes (AZ versus placebo), probablement en rapport avec le fait que les sujets testés étaient peu nombreux et qu’ils avaient moins de 65 ans.

    METHODS
    We conducted a multicenter, double-blind, randomized, controlled trial to assess the safety and efficacy of the ChAdOx1 nCoV-19 vaccine (AZD1222) in people not infected with the human immunodeficiency virus (HIV) in South Africa. Participants 18 to less than 65 years of age were assigned in a 1:1 ratio to receive two doses of vaccine containing 5×1010 viral particles or placebo (0.9% sodium chloride solution) 21 to 35 days apart. Serum samples obtained from 25 participants after the second dose were tested by pseudovirus and live-virus neutralization assays against the original D614G virus and the B.1.351 variant. The primary end points were safety and efficacy of the vaccine against laboratory-confirmed symptomatic coronavirus 2019 illness (Covid-19) more than 14 days after the second dose.

    RESULTS
    Between June 24 and November 9, 2020, we enrolled 2026 HIV-negative adults (median age, 30 years); 1010 and 1011 participants received at least one dose of placebo or vaccine, respectively. Both the pseudovirus and the live-virus neutralization assays showed greater resistance to the B.1.351 variant in serum samples obtained from vaccine recipients than in samples from placebo recipients. In the primary end-point analysis, mild-to-moderate Covid-19 developed in 23 of 717 placebo recipients (3.2%) and in 19 of 750 vaccine recipients (2.5%), for an efficacy of 21.9% (95% confidence interval [CI], −49.9 to 59.8). Among the 42 participants with Covid-19, 39 cases (92.9%) were caused by the B.1.351 variant; vaccine efficacy against this variant, analyzed as a secondary end point, was 10.4% (95% CI, −76.8 to 54.8). The incidence of serious adverse events was balanced between the vaccine and placebo groups.

    CONCLUSIONS
    A two-dose regimen of the ChAdOx1 nCoV-19 vaccine did not show protection against mild-to-moderate Covid-19 due to the B.1.351 variant.

    • Although the mRNA Covid-19 vaccines have modest neutralizing antibody activity after the first dose, they produce a greater increase in neutralizing activity after the second dose than that produced by the ChAdOx1 nCoV-19 and heterologous Sputnik V (adenovirus-26 followed by adenovirus-5 vector) Covid-19 vaccines.5,6,9 Neutralizing activity of the two mRNA vaccines against the B.1.351 variant has also been observed to be lower [voir https://seenthis.net/messages/903588], by a factor of 8.6 (mRNA-1273 vaccine [Moderna]) or 6.5 (BNT-162b2 vaccine [Pfizer]) on pseudovirus neutralization assay, than activity against the D614G virus, whereas no difference was evident against the N510Y.V1 (B.1.1.7)–like mutant.