Omicron variant watch: More hospital risk insight in South African data

South African experts have submitted a new study analysing the early days of the Omicron outbreak in the province, including the first age-wise break-up of hospitalisation rates.

Several cities in India, including Delhi and Mumbai, are now firmly in the middle of an Omicron wave. Both cities are high-density urban centres – bearing some similarities to Gauteng province in South Africa, which is regarded as the epicentre of the highly transmissible variant.

In terms of headline numbers, the report reinforces the conclusion that the variant is leading to less severe cases. (Bloomberg)

Gauteng is also home to Johannesburg, the largest city in South Africa.

South African experts have submitted a new study analysing the early days of the Omicron outbreak in the province, including the first age-wise break-up of hospitalisation rates. The report, undergoing a peer review in The Lancet journal, is based on cases that were recorded in the early phase of the wave between November 14 and December 11, a period when 133,551 Omicron infections are estimated to have taken place.

In terms of headline numbers, the report reinforces the conclusion that the variant is leading to less severe cases: the authors found only 4.9% of cases were hospitalised, compared to 18.9% during the early phase of the Beta variant outbreak and 13.7% during the early phase of the Delta outbreak.

A crucial caveat here is that a large number of people were vaccinated in South Africa between the Delta and Beta waves and the Omicron wave, and experts in the country have previously cited this as a possible factor for the reduced severity.

This appears to bear out in a particular age group: those under 20, most of whom were not eligible for vaccines. “While admission rates during the fourth wave dropped substantially in those aged [over] 20 years in whom vaccination coverage was higher, this was not observed in the largely unvaccinated [under] 20 years age group. In the [less than] 20 years group, the proportions of cases admitted to hospital was similar -- 7.1% (Beta wave) vs 3.8% (Delta wave) vs 6.1% (Omicron wave) -- and the proportion with severe illness among admitted patients, was similar -- 22% vs 23.0% vs 20.4% -- in the three waves, in contrast to the reductions in both admission rates and disease severity observed in the fourth wave in adults,” said the authors from South Africa’s National Institute for Communicable Diseases (NICD) in their report.

“Possible reasons for this could be that children have lower rates of prior infection and/or vaccination,” they added.

The authors add that these were still early findings. “While these considerations apply to the early part of all three waves, these results may not represent the entire Omicron-dominated wave’s disease severity and may change when patient data for this entire wave are available,” they said.

In another study of likely implication for India, researchers in Japan found that hybrid immunity – people vaccinated and previously infected – may have strong protection even in the case of an Omicron variant infection and the longer the gap between an infection and vaccination, the more protection there is likely to be.