Western Cape study shows why Omicron wave caused less death
High rates of vaccination, past infections and the variant itself helped suppress deaths and hospitalisations
18 JANUARY 2022 - 08:30JAMES STENT
File photo: GALLO IMAGES/ER LOMBARD
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new study has shown that the Omicron wave in the Western Cape was much less deadly than previous waves, owing to vaccination, high rates of past infection in the community, and reduced risk of severe disease and death owing to the variant itself.
More than 5,000 adult Covid patients were surveyed during one month of the fourth wave of the pandemic, and were compared to 11,000 patients from previous waves. The researchers were looking to understand the relative risk of each wave of Covid infections, when adjusted to account for vaccination and past infection, as well as age, sex, location and co-morbidities.
The study was led by Prof Mary-Ann Davies, director of the Centre for Infectious Disease Epidemiology & Research at the University of Cape Town, working in collaboration with 46 others from the Western Cape department of health; the national department of health; the National Health Laboratory Service; the Universities of Cape Town, Stellenbosch, the Witwatersrand, and KwaZulu-Natal; the Francis Crick Institute; and Imperial College London. Their paper is a preprint and has not yet been peer-reviewed.
According to the authors, this is “the first study from a setting of high prior seroprevalence to demonstrate less severe disease in wave four”, adjusted for vaccination and prior diagnosed infection. The study sought to answer if past infection or vaccination still protected people exposed to Omicron, and the extent to which this protection was causing milder cases – or if Omicron is inherently less dangerous.
When adjusting for vaccination, there was a 59% reduced risk of death and 28% reduced risk of severe disease from infection during the fourth wave compared to previous waves. This indicates that vaccination is associated with a strongly reduced risk of death and severe disease.
When past infections were taken into account, the risk of hospitalisation and death was reduced by 25%. The authors suggest that this indicates that the Omicron variant is inherently less dangerous than past waves – in particular the Delta-dominated third wave.
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