The Delta variant of COVID-19 is associated with approximately double the risk of hospitalisation compared with the Alpha variant, according to a new nationwide study published as a research letter in The Lancet.
Two vaccine doses still provide strong protection against the Delta variant but it may be at a lower level compared with the Alpha variant, the early evidence suggests.
The research team from Universities of Edinburgh and Strathclyde, and Public Health Scotland, analysed a dataset as part of the EAVE II project, which uses anonymised linked patient data to track the pandemic and the vaccine roll-out in real time.
Based on data analysed from 5.4 million people in Scotland, the Delta variant is now the dominant form of COVID-19 cases in the country, overtaking the Alpha variant, which was first identified in Kent.
During the period studied 1 April to 6 June 2021, there were 19,543 community cases and 377 hospitalisations where a specific variant of COVID-19 was confirmed. Of these totals, 7723 cases and 134 hospitalisations were found to have the Delta variant. People with underlying conditions were more at risk of being hospitalised, researchers said.
Vaccines were found to reduce the risk of being admitted to hospital, but strong protective effects against the Delta variant were not seen until at least 28 days after the first vaccine dose.
In community cases at least 2 weeks after the second dose, the Pfizer/BioNTech vaccine was found to provide 79% protection against infection from the Delta variant, compared with 92% against the Alpha variant.
For the same scenario, the Oxford/AstraZeneca vaccine offered 60% protection against infection with the Delta variant compared with 73% for the Alpha variant. This lower vaccine effect may reflect that is takes longer to develop immunity with Oxford/AstraZeneca, experts say.
The team caution that because of the observational nature of the study, data about vaccine effectiveness should be interpreted with caution and it is not possible to make a direct comparison between both vaccines.
'Substantial Protection'
Professor Aziz Sheikh, director of the University of Edinburgh’s Usher Institute and EAVE II study lead, said: "Over a matter of weeks the Delta variant has become the dominant strain of SARS-CoV-2 in Scotland. It is unfortunately associated with increased risk of hospitalisation from COVID-19. Whilst possibly not as effective as against other variants, two doses of the Pfizer/BioNTech and Oxford/AstraZeneca vaccines still offer substantial protection against the risk of infection and hospitalisation. It is therefore really important that, when offered second doses, people take these up both to protect themselves and to reduce household and community transmission."
Dr Jim McMenamin, COVID-19 National Incident Director for Public Health Scotland added: "These results provide early encouragement that two doses of either Pfizer-BioNTech or Oxford-AstraZeneca vaccines significantly reduce the risk of infection against both the Alpha or new Delta variants. They also show the vaccines offer protection against the risk of hospitalisation with the new Delta variant. Though no vaccine can be 100% protective, they provide the best protection against COVID-19 and it remains important to get both doses when offered."
Commenting via the Science Media centre, Prof Rowland Kao, University of Edinburgh, said: "The fact that both of the two widely available vaccines appear to have some impact on both infection and hospitalisation (albeit reduced for the delta variant) is a reminder of the importance of continued vaccination as this will be one of the most important determinants in whether or not further easing in the future is likely to occur sooner rather than later.
"While hospitalisations are shown to be increased, the paper does not address the issue of demand on intensive care units, or deaths due to the delta variant, as there are as yet insufficient data on this. These will be important determinants for any future decisions on further relaxation or, should they be merited, reintroduction of restrictions. As infections are expected to continue to increase both due to the effects of existing levels of restriction (where R is clearly above 1) and the increased transmissibility of the delta variant, the data on deaths and ICU occupancy will continue to be monitored very closely."
Sheikh A, McMenamin J, Taylor B, Robertson C; on behalf of Public Health Scotland and the EAVE II Collaborators. SARS-CoV-2 Delta VOC in Scotland: demographics, risk of hospital admission, and vaccine effectiveness. Lancet. Published online June 14, 2021. https://doi.org/10.1016/S0140-6736(21)01358-1
Adapted from Univadis, part of the Medscape Professional Network.
