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...Combining results from a community-wide serological survey of 5,310 blood donors and volunteers with SARS-CoV-2 viral load data from city-wide wastewater surveillance, the researchers estimated, (i) vaccine effectiveness against all Omicron BA.2 infections conferred by two, three and four homologous doses of the Comirnaty or CoronaVac vaccines for 100 days after each dose and (ii) COVID-19 infection attack rate in Hong Kong from 1 January to 31 July 2022. The researchers developed two in-house ELISA assays detecting IgG antibodies to the nucleocapsid (N) or Open Reading Frame 8 (ORF8) protein of SARS-CoV-2, with the latter assay developed specifically to detect...

...Between 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...vaccine effectiveness against symptomatic disease was higher for the delta variant than for the omicron variant. No effect against the omicron variant was noted from 20 weeks after two ChAdOx1 nCoV-19 doses, whereas vaccine effectiveness after two BNT162b2 doses was 65.5% (95% confidence interval [CI], 63.9 to 67.0) at 2 to 4 weeks, dropping to 8.8% (95% CI, 7.0 to 10.5) at 25 or more weeks. Among...

Experts are puzzled by a new study in which influenza vaccination seemed to provide little or no protection against flu in the 2010-11 season—and in which the only participants who seemed to benefit from the vaccine were those who hadn't been vaccinated the season before. The investigators recruited 328 households in Michigan before the flu season started and followed them through the season. Overall, they found that the infection risk was nearly the same in vaccinated and unvaccinated participants, indicating no significant vaccine-induced protection, according to their report in Clinical Infectious Diseases. That contrasted sharply with several other observational studies...