Infectious Disease
Under-reporting of SARS-CoV-2 Infections in 27 Countries, 2020–2022. Kate Devlin* Mustapha Mustapha Kanae Togo Hannah R Volkman Jingyan Yang Alon Yehoshua Manuela Di Fusco John M McLaughlin Jennifer L Nguyen
Background
It is increasingly difficult to obtain reliable estimates of SARS-CoV-2 infections post-pandemic. In this study we quantified under-reporting of SARS-CoV-2 infections and assessed reporting trends across countries and by variant.
Methods
Using data from the Institute for Health Metrics and Evaluation (IHME) on reported and estimated total SARS-CoV-2 infections from February 2020– December 2022 in 27 countries, we calculated the under-reporting factor (UF), defined as the number of unreported infections per reported infection (regardless of symptom status).
Findings
In the 27 included countries, there were over 2.5 billion estimated infections but only 372.6 million reported infections, indicating over 2.2 billion unreported infections. UF varied considerably among countries, with overall median UF ranging from 1.1–27.5 unreported infections per reported infection during the pandemic. UF was highest during Omicron predominance (range of medians: 0.1–3.3, 0.3–14.6, and 2.1–187.7 during Alpha, Delta, and Omicron, respectively), particularly during BA.4/5 (range of medians: 2.5–244.3). UFs were generally lowest in European countries followed by North America, Middle East, East and Southeast Asia while South Africa and countries in South America generally had the highest UF.
Interpretation
SARS-CoV-2 infections are substantially under-reported globally. Under-reporting was highest during Omicron predominance, particularly during BA.4/5 predominance, and much lower during Alpha and Delta predominance. We found that the total number of SARS-CoV-2 infections during BA.4/5 predominance was 2.5–244.3 times higher than reported in the 27 included countries. Our findings for the BA.4/5 predominance period are likely relevant to the current post-pandemic setting given the absence of public health mandates and changes in testing behaviors during BA.4/5 predominance through present-day.
Funding
This study was sponsored by Pfizer.