Fig. 4: The infection fatality ratios and the factors associated with SARS-CoV-2 disease severity for different epidemic waves in the urban site’s district.

A The estimated infection fatality ratio for each epidemic wave. B The mortality burden of each epidemic wave measured by the cumulative rate of in-hospital deaths per 100 individuals. C The infection attack rate of each epidemic wave in the North West based on the PHIRST-C urban cohort, assuming that the urban cohort population is representative of the population of the North West Province. D The wave-specific distribution of infection types based on prior exposure histories, including primary infection, vaccine breakthroughs (1 or 2 doses of vaccines), reinfections (infection after one prior infection), and multiple prior exposures (infection with two or more prior infections or a mixture of prior infection and vaccination). E The wave-specific age distribution of infections. F The wave-specific distribution of variant type among infections. B–F Share the same axis on the right. *For the 4th wave, we could not confirm variant type by variant-specific rRT-PCR or sequencing, however, judging from the timing of emergence and dominance of Omicron in South Africa in late November 2021, we assumed here that all infections during the 4th wave were due to Omicron BA.1/2 variants.