A new analysis released Monday by Public Health England (PHE) shows for the first time that two doses of COVID-19 vaccines are very effective against hospitalisation caused by the highly transmissible Delta (B.1.617.2) variant of SARS-CoV-2 first detected in India. The agency had previously found that a single dose is 17% less effective at preventing symptomatic COVID-19 from Delta, compared to the Alpha (B.1.1.7) strain that surfaced last year in the UK, but said there is only a "small difference" after two doses.
Its latest analysis looked at 14,019 infections with the Delta variant in England in the period from April 12 to June 4, with 166 of these winding up in hospital. The PHE calculated that the Pfizer-BioNTech vaccine Comirnaty was 96% effective at preventing hospitalisations due to the Delta variant after two doses, while AstraZeneca's Vaxzevria was 92% against hospitalisations after two doses.
According to the agency, these findings are comparable with vaccine effectiveness against hospitalisation from Alpha. "Further work remains underway to establish the level of protection against mortality from the Delta variant," but the PHE indicated that "as with other variants, this is expected to be high."
Meanwhile, a separate analysis, published Monday as correspondence in The Lancet by public health officials in Scotland, also looked at how Comirnaty and Vaxzevria fared against the Delta strain in that country. In the period from April 1 to June 6, there were 19,543 confirmed SARS-CoV-2 infections in Scotland, with 377 admitted to hospital. Researchers found a reduction in vaccine effectiveness against cases caused by Delta compared with earlier strains, but similar levels of protection against severe illness.
Specifically, they estimated that two doses of Comirnaty cut the risk of infection with Alpha by 92%, whereas that fell to 79% for the Delta variant, while for Vaxzevria, the figures were 73% and 60%, respectively. Further, the Scottish analysis determined that the risk of hospitalisation with Delta was lowered by around 70% after two doses of either vaccine. Aziz Sheikh, lead author of the Scottish analysis, remarked that "vaccine effectiveness against Delta is still very, very substantial."
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