Omicron is less serious even for the unvaccinated, according to study

The omicron variant of the coronavirus causes less severe disease than the delta variant, even in those who are not vaccinated or who have not had a previous COVID-19 infection, according to a study from South Africa’s Western Cape province.

The research in the region where Cape Town is the capital compared 11,609 patients from the first three waves of infection, the most recent of which was caused by the delta variant, and 5,144 patients from the latest omicron-driven wave.

The findings add to mounting evidence that while more infectious, omicron may be less virulent than some of its predecessors. Data from South Africa, the first country to have a major outbreak caused by the variant, has so far shown lower rates of hospitalization and death.

Still, with more than a quarter of the population vaccinated and a prior infection rate of 70% to 80%, there is concern that may be masking the danger posed by the variant.

“Ours is the first study from a prior high seroprevalence setting to demonstrate less severe disease in the fourth wave, after adjusting for both vaccination and previously diagnosed infection.”, the researchers said in the study. “Even after this protection was considered, there was a likely reduction in the most severe outcomes in the fourth wave.”, indicating a possible reduction in the virulence of omicron, the study said.

less deadly

The study, which was published this week and has not yet been peer-reviewed, focused on public hospitals in the province. It was led by Mary Ann-Davies, Associate Professor at the University of Cape Town. It is also affiliated with the Western Cape Government Health Impact Assessment Inspectorate.

The study found that 8% of people were hospitalized or died within 14 days of being diagnosed with COVID-19 in the omicron-driven wave compared to 16.5% in the previous three waves.

“After adjusting for age, sex, comorbidities, and subdistrict, there was a substantially lower risk of death in the fourth wave compared to the third wave.”, the researchers said. “The extent of the reduction was attenuated when additionally considering vaccines and previously diagnosed infections.”

Still, even when prior infections were taken into account, there was a 25% lower risk of dying in wave four than in wave three, they said. However, after adjustments were made for immunity from previous vaccinations or infections, omicron presented a similar risk to the version of the virus first identified in Wuhan, China.

In separate data, released Friday by the South African National Institute of Communicable Diseases, researcher Waasila Jassat said national deaths from COVID-19 had peaked at 14% to 15% of the rate seen in the delta wave. Hospital admissions peaked at around 60% of the delta wave, he said in an online presentation.

The researchers cautioned that given the infectious nature of omicron, public health systems still need to carefully plan for outbreaks due to the potential increase in patients.

“We found substantially reduced disease severity among diagnosed COVID-19 cases in the fourth omicron-driven wave, compared to previous waves”, the researchers said. Even taking into account previous vaccinations and infections, the data suggest a “intrinsically reduced virulence of omicron”.