High immunity, low vaccine rate in South Africa point to prior infectionsA seroepidemiologic survey of 7,010 people in Gauteng province, South Africa, before the SARS-CoV-2 Omicron variant outcompeted the Delta strain shows that 80% of those older than 50 years had antibodies against the virus, with most seropositivity likely generated by previous infection.In the study, published yesterday in the New England Journal of Medicine (NEJM), South African researchers analyzed dried-blood samples from participants from 3,047 households from Oct 22 to Dec 9, 2021.
They looked for anti–SARS-CoV-2 immunoglobulin G (IgG) antibodies and assessed COVID-19 cases, hospitalizations, and deaths and excess deaths through Jan 12, 2022.
Omicron was first identified in the region on Nov 25, 2021, but didn't become dominant until December.Of the 7,010 participants, 18.8% had been vaccinated against COVID-19.
IgG seroprevalence ranged from 56.2% (95% confidence interval [CI], 52.6% to 59.7%) among children younger than 12 years to 79.7% (95% CI, 77.6% to 81.5%) in adults older than 50.