At all time points investigated and for all combinations of primary course and booster vaccines, vaccine effectiveness against symptomatic disease was higher for the delta variant than for the omicron variant. Vaccine effectiveness was calculated after primary immunization with two doses of BNT162b2 (Pfizer-BioNTech), ChAdOx1 nCoV-19 (AstraZeneca), or mRNA-1273 (Moderna) vaccine and after a booster dose of BNT162b2, ChAdOx1 nCoV-19, or mRNA-1273.īetween November 27, 2021, and January 12, 2022, a total of 886,774 eligible persons infected with the omicron variant, 204,154 eligible persons infected with the delta variant, and 1,572,621 eligible test-negative controls were identified. We used a test-negative case-control design to estimate vaccine effectiveness against symptomatic disease caused by the omicron and delta (B.1.617.2) variants in England. Thomas's Hospital NHS Trust (M.C.), London, Wellcome Sanger Institute, Hinxton (J.C.B.), and Healthcare Associated Infections and Antimicrobial Resistance, University of Oxford, Oxford (S.H.) - all in the United Kingdom.Ī rapid increase in coronavirus disease 2019 (Covid-19) cases due to the omicron (B.1.1.529) variant of severe acute respiratory syndrome coronavirus 2 in highly vaccinated populations has aroused concerns about the effectiveness of current vaccines. George's University of London (R.M., S.N.L.), the Medical Research Council Centre for Global Infectious Disease Analysis (N.F.) and the NIHR Health Protection Research Unit in Respiratory Infections (N.F., M.Z., J.L.B.), Imperial College London, and Guy's and St. Thelwall, G.D., R.M., G.A., S.G., R.E., S.N.L., M.Z., C.N.J.C., K.B., S.H., M.C., M.R., J.L.B.), the National Institute for Health Research (NIHR) Health Protection Research Unit in Vaccines and Immunisation, London School of Hygiene and Tropical Medicine (N.A., G.A., C.N.J.C., K.B., M.R., J.L.B.), the Paediatric Infectious Diseases Research Group, St. Health Security Agency (N.A., J.S., F.K., S.
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