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Reduced neutralisation of SARS-CoV-2 omicron B.1.1.529 variant by post-immunisation serum

At present, delta variant is estimated to have caused more than 99% of COVID-19 infections worldwide; however, a new variant of concern, omicron (B.1.1.529), was reported first in South Africa on Nov 24, 2021, but has since been reported in multiple countries.

Early reports from South Africa suggest that omicron is highly transmissible, in a population where 60–80% already show serological evidence of previous infection or vaccination, suggesting that omicron is able to break through natural and vaccine-induced immunity; although early reports do not indicate more severe disease.
In this article the authors report the results of neutralisation assays using an isolate of omicron obtained from an infected case in the UK. Neutralisation assays were done on sera from individuals from the immunology cohort of the Com-COV2 study, who were seronegative at enrolment (defined by anti-nucleocapsid IgG). Participants were vaccinated with two doses of Oxford–AstraZeneca’s ChAdOx1 nCoV-19 (ChAd; n=22), or two doses of Pfizer–BioNTech’s BNT162b2 (BNT; n=21). Samples were obtained 28 days (range 25–32) following the second immunisation. The authors found a substantial decrease in neutralisation titre in recipients of both homologous ChAd and BNT primary courses, with evidence of some recipients not neutralising at all. This reduction in neutralisation titre will probably be more pronounced at later timepoints.
Dejnirattisai W, Shaw RH, Supasa P, Liu C, Stuart AS, Pollard AJ, Liu X, Lambe T, Crook D, Stuart DI, Mongkolsapaya J, Nguyen-Van-Tam JS, Snape MD, Screaton GR; Com-COV2 study group. Reduced neutralisation of SARS-CoV-2 omicron B.1.1.529 variant by post-immunisation serum. Lancet. 2021 Dec 20:S0140-6736(21)02844-0.

doi: 10.1016/S0140-6736(21)02844-0

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