SARS-CoV-2 Omicron Symptomatic Infections in Previously Infected or Vaccinated South African Healthcare Workers

Abstract

We investigated Omicron infections among healthcare workers (HCW) presenting with symptoms of SARS-CoV-2 infection and evaluated the protective effect of vaccination or prior infection. Between 24 November and 31 December 2021, HCW in Johannesburg, South Africa, were tested for SARS-CoV-2 infection by Nucleic Acid Amplification Test (NAAT). Blood samples collected either at the symptomatic visit or in the 3 months prior, were tested for spike protein immunoglobulin G (IgG). Overall, 433 symptomatic HCW were included in the analysis, with 190 (43.9%) having an Omicron infection; 69 (16.7%) were unvaccinated and 270 (62.4%) received a single dose of the Ad26.COV.2 vaccine. There was no difference in the odds of identifying Omicron between unvaccinated and Ad26.COV.2 vaccinated HCW (adjusted odds ratio (aOR) 0.81, 95% confidence interval (CI): 0.46, 1.43). One-hundred and fifty-four (35.3%) HCW had at least one SARS-CoV-2 NAAT-confirmed prior infection; these had lower odds of Omicron infection compared with those without past infection (aOR 0.55, 95%CI: 0.36, 0.84). Anti-spike IgG concentration of 1549 binding antibody unit/mL was suggestive of significant reduction in the risk of symptomatic Omicron infection. We found high reinfection and vaccine breakthrough infection rates with the Omicron variant among HCW. Prior infection and high anti-spike IgG concentration were protective against Omicron infection.

COVID-19 in non-hospitalised adults caused by either SARS-CoV-2 sub-variants Omicron BA.1, BA.2, BA.5 or Delta associates with similar illness duration, symptom severity and viral kinetics, irrespective of vaccination history

“…These results are consistent with self-reported symptom data during the BA.1 wave from the ZOE study, a large smartphone app-based community study in the UK and are supportive of the expansion of cardinal symptoms by the NHS in its COVID-19 guidance issued in April 2022 (13,15). Despite analyses of hospitalisation and mortality data indicating that Omicron caused lesssevere clinical disease (7,8,10), our data suggests that COVID-19 continues to cause a significant symptom burden in non-hospitalised adults with COVID-19, with attendant impacts on healthcare resources, and incidence of post-COVID syndrome (PCS) (11,12). This continued burden is well-illustrated by the shift in the numbers of asymptomatic cases we .…”

Percentage of Asymptomatic Infections among SARS-CoV-2 Omicron Variant-Positive Individuals: A Systematic Review and Meta-Analysis

“…Most individuals infected with COVID-19 before are likely to be reinfected due to the increased immune escape capability of the Omicron variant, which may cause a higher percentage of asymptomatic infections [ 46 , 47 ]. Previous studies showed that the Omicron variant-positive individuals with booster doses of vaccines had a lower percentage of severe symptoms and a higher percentage of no symptoms or mild symptoms [ 48 , 49 ]. This suggests that the current vaccine is still effective in preventing severe cases but seems to be less effective in preventing Omicron infections.…”

Vaccine Breakthrough Infection with the SARS-CoV-2 Delta or Omicron (BA.1) Variant Leads to Distinct Profiles of Neutralizing Antibody Responses

“…The Omicron variant has overtaken the globe faster than any previous SARS-CoV-2 variant 20 . Its increased fitness appears linked, at least in part, to its extensive antibody evasion properties and ability to cause vaccine breakthrough infections 21 and reinfections 5 . Initially, most Omicron cases were caused by BA.1, but the BA.2 variant appears to have a higher growth rate in most populations and is replacing BA.1 as the dominant variant in many locations 22,23 .…”

“…Breakthrough infection following SARS-CoV-2 vaccination has been observed since the rollout of vaccines 1,2 and has been associated with specific variants including Beta 3 , Delta 4 , and Omicron 5 . The predisposing factors to breakthrough infection and the consequences of breakthrough infection for SARS-CoV-2 immunity are poorly understood.…”