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

Abstract

Background: Asymptomatic infections are potential sources of transmission for coronavirus disease 2019, especially during the epidemic of the SARS-CoV-2 Omicron variant. We aimed to assess the percentage of asymptomatic infections among SARS-CoV-2 Omicron variant-positive individuals detected by gene sequencing or specific polymerase chain reaction (PCR). Methods: We searched PubMed, EMBASE, and Web of Science from 26 November 2021 to 13 April 2022. This meta-analysis was conducted following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines and was registered with PROSPERO (CRD42022327894). Three researchers independently extracted data and two researchers assessed quality using pre-specified criteria. The pooled percentage with 95% confidence interval (CI) of asymptomatic infections of SARS-CoV-2 Omicron was estimated using random-effects models. Results: Our meta-analysis included eight eligible studies, covering 7640 Omicron variant-positive individuals with 2190 asymptomatic infections. The pooled percentage of asymptomatic infections was 32.40% (95% CI: 25.30–39.51%) among SARS-CoV-2 Omicron variant-positive individuals, which was higher in the population in developing countries (38.93%; 95% CI: 19.75–58.11%), with vaccine coverage ≥ 80% (35.93%; 95% CI: 25.36–46.51%), with a travel history (40.05%; 95% CI: 7.59–72.51%), community infection (37.97%; 95% CI: 10.07–65.87%), and with a median age < 20 years (43.75%; 95% CI: 38.45–49.05%). Conclusion: In this systematic review and meta-analysis, the pooled percentage of asymptomatic infections was 32.40% among SARS-CoV-2 Omicron variant-positive individuals. The people who were vaccinated, young (median age < 20 years), had a travel history, and were infected outside of a clinical setting (community infection) had higher percentages of asymptomatic infections. Screening is required to prevent clustered epidemics or sustained community transmission caused by asymptomatic infections of Omicron variants, especially for countries and regions that have successfully controlled SARS-CoV-2.

Safety and immunogenicity of a bivalent SARS-CoV-2 protein booster vaccine, SCTV01C, in adults previously vaccinated with mRNA vaccine: a randomized, double-blind, placebo-controlled phase 1/2 clinical trial

“…According to published reports, asymptomatic infections accounted for approximately 32.4%–45% of Omicron infections. 29 , 30 We observed highly diversified baseline neutralizing antibody titers to both Delta and Omicron variants prior to boosting with SCTV01C. About 90% of the participants showed positive PRNT50 (above lower limit of quantitation LLOQ: 20) of neutralizing antibody to live Omicron, which were much higher than previously reported for people vaccinated with two doses of mRNA vaccines.…”

Seroprevalence of anti-SARS-CoV-2 IgG antibodies in Tyrol, Austria: Updated analysis involving 22,607 blood donors covering the period October 2021 to April 2022

“…Several studies reported lower humoral immune responses after an infection with Omicron compared to other variants. This could be associated with milder symptoms caused by Omicron infections [27][28][29][30][31], since higher antibody levels and its persistence are correlated with disease severity in COVID-19 [15,16]. Recently, a study observed a lower humoral immune response after infection in Omicron convalescent individuals compared to individuals with two-dose mRNA vaccinations [14].…”

“…Between October 2021 and April 2022, these waves have cumulatively led to 310,308 cases of infection, corresponding to an estimated 35-40% of the general population [25,26]. Furthermore, infection with the Omicron variant is more commonly asymptomatic or paucisymptomatic [27][28][29][30][31] and therefore it is plausible that cases of Omicron infection more commonly remain undetected than infections with earlier variants, which suggests that the "true" number of cases is probably even higher. The impact of the high number of infections during winter 2021/2022 on the current seroepidemiological status of the population is likely to be substantial but remains to be determined reliably in an up-to-date seroepidemiological study.…”

PCR-like Performance of Rapid Test with Permselective Tunable Nanotrap

“…Reportedly, the pooled percentage of asymptomatic infections was 32.40% in Omicron. 30 We also checked the ability to test asymptomatic individuals. Most samples were collected under the Institutional Review Board of Seoul St. Mary's hospital (KC21TIDI0134K).…”