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Immunity before and after SARS-CoV-2 Omicron variant in South Africa


In a recent study published in the New England Journal of Medicine researchers conducted a national epidemiological survey to determine seropositivity against severe acute respiratory syndrome (SARS-CoV-2) prior to the emergence of the concerning new variant of Omicron (VOC).

They also analyzed the change in the epidemiological scenario of the fourth wave of the coronavirus disease 2019 (COVID-19) pandemic in Gauteng Province in South Africa.

Study: Population immunity and severity of Covid-19 with the Omicron variant in South Africa. Image Credit: G.Tbov/Shutterstock

Since its appearance on November 25, 2021 in South Africa, Omicron’s highly mutated COV has caused considerable mortality across the world. The presence of more than 32 mutations in the spike protein (S), three mutations in the membrane protein (M) and six mutations in the nucleocapsid protein (N) of Omicron conferred an increased ability to evade the neutralizing effects of host immunoglobulin. -G (IgG).

Previous studies have reported the epidemiological trends associated with earlier VOCs such as Beta and Delta variants in South Africa. The present study is a follow-up study to add to the results of the epidemiological evaluation of the Omicron-dominant COVID-19 fourth wave.

About the study

This survey was conducted between October 22, 2021 and December 9, 2021 to assess the fourth wave epidemiology and determine seropositivity against Omicron COV S and N proteins among Gauteng residents.

Data on positive cases, hospital admissions and deaths from the onset of COVID-19 to 12 January 2022 were obtained from the Daily Hospital Surveillance Database (DATCOV), South African Council of Medical Research and the South African National Institute of Communicable Diseases using an electronic system. questionnaire method. Considering sample size attrition due to death or people migrating to other countries, household contacts who participated in a similar survey conducted between November 2020 and January 2021 were included in the survey. ‘study.

For determination of seropositivity, blood was collected from participants after ethical and informed consent was obtained. Blood samples were examined for the presence of anti-spike and anti-nucleocapsid IgG antibodies using serological tests.

Results and discussion

A total of 7,948 people completed the questionnaire. However, only 7010 samples were analyzed after exclusion of duplicate and inadequate samples. Only 18.8% of these 7,010 participants were vaccinated.

Overall, 73.1% seropositivity was observed, with seroprevalence rates being higher in the vaccinated (93.1%) than in the unvaccinated (68.4%). Adults aged 50 or over were more seropositive (79.7%) than children under 12 (56.2%). Seroprevalence was heterogeneous between districts, with the highest values ​​in Johannesburg (76.2%). Men, smokers, and unvaccinated people over the age of 50 with no history of SARS-CoV-2 infection residing in informal communities were most susceptible to COVID-19.

Prior to the Omicron wave, 36% and 20% of Gauteng residents were single and double vaccinated, respectively, as of November 25, 2021. Unlike previous COVID-19 waves, a significantly high incidence (2.26,932 cases) was noted with the Omicron wave, while the degree of severity, in terms of hospitalizations (11.2%) and deaths (7.2%), was lower. There was a rapid increase in Omicron-induced cases that peaked within a month, compared to the two-month peak during the third wave. The Omicron-dominant wave was coming to an end around January 12, 2022.

The high seropositivity rates observed prior to the emergence of the Omicron COV may be due to the cumulative effect of the development of robust natural active humoral responses and long-term T cell-mediated immunity developed in response to infection. prior to COVID-19, and natural passive immunity. vaccine-acquired immunity.

Higher incidence of SARS-CoV-2 but lower severity seen in the pandemic’s fourth wave of COVID-19 could be due to higher viral transmissibility and immune evasion properties, but higher potency. low VOC Omicron genetically mutated against SARS-CoV-2 neutralizing antibodies, specifically anti-S IgG.


In summary, a high seroprevalence was noted in females 18-50 years old, vaccinated, Gauteng population residing in self-contained, non-smoking homes, likely due to hybrid immunity developed in response to previous COVID-19 infections. 19 and administration of the vaccine. .

Although the presence of anti-N IgG antibodies in serum positively indicates current infection, anti-S IgG antibodies should be used in serological testing to determine if an individual has previously been diagnosed with COVID-19.

While the new Omicron variant was more transmissible than other COVs such as beta and delta, it caused less severe disease reflected in a drastic decrease in morbidity and mortality associated with SARS-CoV-2 in the fourth wave of Omicron-dominant COVID-19.