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Widespread population immunity of Covid-19 observed in South Africa before Omicron wave

1. Wide­spread under­ly­ing SARS-CoV­‑2 seropos­i­tiv­i­ty was observed in Gaut­eng province, South Africa, before the omi­cron wave.
2. Epi­demi­o­log­ic data demon­strat­ed a decou­pling of hos­pi­tal­iza­tions and deaths from infec­tions while omi­cron was circulating.
Evi­dence Rat­ing Lev­el: 2 (Good)
Study Run­down: The Omi­cron vari­ant was first iden­ti­fied in Novem­ber 2021 in Gaut­eng province, South Africa, and was des­ig­nat­ed as a vari­ant of con­cern due to its pre­dict­ed high trans­mis­si­bil­i­ty and its poten­tial to evade immu­ni­ty from neu­tral­iz­ing anti­bod­ies induced by vac­ci­na­tion or nat­ur­al infec­tion with wild-type virus. The omi­cron vari­ant out­com­pet­ed the delta vari­ant in Gaut­eng and was respon­si­ble for 98.4% of the cas­es sequenced in South Africa in Decem­ber 2021, and a pri­or pop­u­la­tion-wide sero­epi­de­mi­o­log­ic study demon­strate that 19.1% of the pop­u­la­tion was seropos­i­tive for Covid-19. How­ev­er, there is a gap in knowl­edge as to under­stand­ing the sero­preva­lence of Covid-19 before the omi­cron wave. This study found that there was wide­spread under­ly­ing SARS-CoV­‑2 seropos­i­tiv­i­ty in Gaut­eng before the omi­cron-dom­i­nant wave of Covid-19. This study was lim­it­ed by changes in the fre­quen­cy of test­ing over time which lim­it­ed head-to-head com­par­isons of case num­bers across waves, and the fourth omi­cron wave had not ful­ly sub­sided at the time of this analy­sis, which will result in a lag in the report­ing of data such as hos­pi­tal­iza­tions and deaths attrib­ut­able to this wave. Nev­er­the­less, these study’s find­ings are sig­nif­i­cant, as they demon­strate that there was wide­spread seropos­i­tiv­i­ty of Covid-19 in Gaut­eng pri­or to the omi­cron wave and that there was a decou­pling of hos­pi­tal­iza­tions and deaths from infec­tions while omi­cron was circulating.
Click to read the study in NEJM
Rel­e­vant Read­ing: Omi­cron — Decou­pling Infec­tion from Severe Disease
In-Depth [sero­epi­de­mi­o­log­ic sur­vey]: This sero­epi­de­mi­o­log­ic sur­vey was con­duct­ed from Octo­ber to Decem­ber 2021 in Gaut­eng province, South Africa, to deter­mine the sero­preva­lence of SARS-CoV­‑2 IgG, obtain­ing sam­ples from 7010 par­tic­i­pants, of whom 18.8% had received a Covid-19 vac­cine. Patients who live in the Gaut­eng province and were able to pro­vide writ­ten informed con­sent were eli­gi­ble for the study. Patients who resided out­side of the stud­ied province or declined to par­tic­i­pate were exclud­ed from the study. The pri­ma­ry out­come mea­sured was sero­preva­lence mea­sured with dried-blood-spot sam­ples and test­ed for IgG against SARS-CoV­‑2 spike pro­tein and nucle­o­cap­sid pro­tein. Out­comes in the pri­ma­ry analy­sis were assessed via unad­just­ed, uni­vari­able analy­ses for each risk fac­tor with gen­er­al­ized lin­ear mod­els with a log link to esti­mate risk ratios. Based on the analy­sis, the sero­preva­lence of SARS-CoV­‑2 IgG ranged from 56.2% among chil­dren younger than 12 years (95% Con­fi­dence Inter­val [CI], 52.6 to 59.7) to 79.7% among adults old­er than 50 years of age (95% CI, 77.6 to 81.5). 93.1% of vac­ci­nat­ed par­tic­i­pants were seropos­i­tive for SARS-CoV­‑2 while 68.4% of unvac­ci­nat­ed par­tic­i­pants were seropos­i­tive. Epi­demi­o­log­ic data also demon­strat­ed that the inci­dence of Covid-19 infec­tion increased and sub­se­quent­ly decreased more rapid­ly dur­ing the omi­cron wave than it had dur­ing the three pre­vi­ous waves. The inci­dence of infec­tion was decou­pled from the inci­dences of hos­pi­tal­iza­tion, record­ed death, and excess death dur­ing the fourth wave, as com­pared to the pro­por­tions seen in the pre­vi­ous three waves. Over­all, this study demon­strat­ed that there was wide­spread Covid-19 seropos­i­tiv­i­ty in the Gaut­eng province of South Africa before the omi­cron wave, show­ing that there was a decou­pling of hos­pi­tal­iza­tions and deaths from Covid-19 infec­tions while the omi­cron vari­ant was still circulating.
Image: PD
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