The following is a summary of “Impact of disease severity, age, sex, comorbidity, and vaccination on secondary attack rates of SARS-CoV-2: a global systematic review and meta-analysis,” published in the February 2025 issue of BMC Infectious Diseases by Sumsuzzman et al.
Understanding the key drivers of SARS-CoV-2 transmission has been vital for public health strategies, but the risk varies according to disease severity, age, sex, comorbidities, and vaccination status across populations and regions.
Researchers conducted a retrospective study to quantify the impact of various factors on secondary attack rates (SARs) of SARS-CoV-2 across diverse populations and regions and identify key transmission determinants to guide targeted interventions for pandemic response.
They searched Ovid MEDLINE, Ovid Embase, Web of Science, and the Cochrane COVID-19 Study Register from January 1, 2020, to January 18, 2024, to identify studies estimating SARs of SARS-CoV-2, defined as the proportion of infected close contacts. The SAR estimates were pooled using a random-effects model with the Freeman-Tukey double arcsine transformation, and Clopper-Pearson 95% CIs were calculated. The risk of bias was evaluated using a modified Newcastle–Ottawa scale and the study was registered with PROSPERO (CRD42024503782).
The results showed 159 studies included over 19 million close contacts and 6.8 million cases from 41 countries across 5 continents, SARs increased with disease severity, ranging from 10% (95% CI: 6%–14%; I2 (= 99.65%) in asymptomatic cases to 15% (95% CI: 9%–21%; I2 = 92.49%) in severe or critical cases while, SARs were lowest at 20% (95% CI: 16%–23%; I2 = 99.44%) for close contacts under 18 years and highest at 29% (95% CI: 24%–34%; I2 = 99.65%) for index cases aged 65 years or older. Among variants, SARs were highest for Omicron and lowest for Delta, decreasing with more vaccine doses. Regionally, North America had the highest SAR at 27% (95% CI: 24%–30%; I2 = 99.31%), surpassing Europe (19%; 95% CI: 15%–25%; I2 = 99.99%), Southeast Asia (18%; 95% CI: 13%–24%; I2 = 99.24%), and the Western Pacific (11%; 95% CI: 8%–15%; I2 = 99.95%). Among close contacts with comorbidities, SARs were highest for chronic lung disease and hypertension, while no significant association was observed with sex.
Investigators concluded the SARs varied by demographic and regional characteristics, emphasizing the role of booster vaccinations in reducing the transmission.
Source bmcinfectdis.biomedcentral.com/articles/10.1186/s12879-025-10610-5
