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Johannesburg, Jan. 3 (PTI): Infections caused by the Omicron variant of the coronavirus in South Africa were milder compared to those in earlier waves, while hospitalisation rates were lower, according to a study.
The yet-to-be peer-reviewed study, posted as preprint in The Lancet, analysed the clinical severity of patients hospitalised with SARS-CoV-2 infection during the first four weeks of the Omicron-dominated fourth wave.
The researchers at the National Institute for Communicable Diseases in South Africa and colleagues from other institutes compared the severity to the first four weeks of the Beta dominated second and Delta-dominated third waves in Gauteng Province.
They collated daily polymerase chain reaction (PCR) and antigen positive SARS-CoV-2 case data from laboratory reports.
Data on hospital admissions were collected through a surveillance programme established specifically for Covid-19. Mathematical models were used to compare disease severity in the three wave periods.
Severe disease was defined as one or more of acute respiratory distress, supplemental oxygen, mechanical ventilation, intensive care or death.
The study found that there were 41,046, 33,423, and 133,551 SARS-CoV-2 cases in the second, third and fourth waves respectively.
About 4.9 per cent of cases were admitted to hospital during the fourth wave compared to 18.9 per cent and 13.7 per cent during the second and third waves, the researchers said.
During the fourth wave, 28.8 per cent of admissions were severe disease compared to 60.1 per cent and 66.9 per cent in the second and third waves, they said.
Admitted patients in the Omicron-dominated fourth wave were 73 per cent less likely to have severe disease than patients admitted during the Delta-dominated third wave, according to the researchers.
"The proportion of cases admitted was lower and those admitted were less severe during the first four weeks of the Omicron-dominated fourth wave in Gauteng province of South Africa," the authors of the study noted.
"Since any combination of a less-virulent virus, comorbidities, high immunity from prior infection(s) or vaccination may be important contributors to this clinical presentation, care should be taken in extrapolating this to other populations with different co-morbidity profiles, prevalence of prior infection and vaccination coverage," they added.