Abstract:
BACKGROUND : In this study, we compared admission incidence risk and the risk of mortality in the Omicron BA.4/BA.5 wave to
previous waves.
METHODS : Data from South Africa’s SARS-CoV-2 case linelist, national COVID-19 hospital surveillance system, and Electronic
Vaccine Data System were linked and analyzed. Wave periods were defined when the country passed a weekly incidence of 30 cases/
100 000 population. In-hospital case fatality ratios (CFRs) during the Delta, Omicron BA.1/BA.2, and Omicron BA.4/BA.5 waves
were compared using post-imputation random effect multivariable logistic regression models.
RESULTS : The CFR was 25.9% (N=37 538 of 144 778), 10.9% (N=6123 of 56 384), and 8.2% (N=1212 of 14 879) in the Delta,
Omicron BA.1/BA.2, and Omicron BA.4/BA.5 waves, respectively. After adjusting for age, sex, race, comorbidities, health sector,
and province, compared with the Omicron BA.4/BA.5 wave, patients had higher risk of mortality in the Omicron BA.1/BA.2 wave
(adjusted odds ratio [aOR], 1.3; 95% confidence interval [CI]: 1.2–1.4) and Delta wave (aOR, 3.0; 95% CI: 2.8–3.2). Being partially
vaccinated (aOR, 0.9; 95% CI: .9–.9), fully vaccinated (aOR, 0.6; 95% CI: .6–.7), and boosted (aOR, 0.4; 95% CI: .4–.5) and having
prior laboratory-confirmed infection (aOR, 0.4; 95% CI: .3–.4) were associated with reduced risks of mortality.
CONCLUSIONS : Overall, admission incidence risk and in-hospital mortality, which had increased progressively in South Africa’s
first 3 waves, decreased in the fourth Omicron BA.1/BA.2 wave and declined even further in the fifth Omicron BA.4/BA.5 wave.
Mortality risk was lower in those with natural infection and vaccination, declining further as the number of vaccine doses increased.
