A joint study by the World Health Organisation’s (WHO) Unity Studies and SeroTracker and colleagues suggests that based on seroprevalence, global Covid-19 infection rates are likely to be higher than previously reported.
The study, published in the open access journal PLOS Medicine, found that global seroprevalence rose from 7.7 per cent in June 2020 to 59.2 per cent in September 2021, suggesting two-thirds of the global population may be SARS-CoV-2 seropositive from either vaccination or infection.
Estimates of Covid-19 infections based on seroprevalence data far exceed reported cases, suggesting a bigger global impact of Covid-19 than previously known.
According to the authors, “this study on global seroprevalence of SARS-CoV-2 antibodies found that while seroprevalence has increased over time, a third of the global population tested negative for antibodies against the virus as of September 2021 estimates. It was also found that compared to seroprevalence estimates, routine testing for Covid-19 has largely underestimated the number of global infections”.
Serosurveillance provides estimates of antibody levels against infectious diseases and is considered the gold standard for measuring population immunity due to past infection or vaccination.
In order to ascertain the true rates of infection and indicators of immunity in the population against SARS-CoV-2 over time, researchers conducted a systematic review and meta-analysis of seroprevalence studies published from January 1, 2020 to May 20, 2022.
From their search parameters, the authors identified 965 distinct seroprevalence studies sampling 5,346,069 participants between January 2020 and April 2022, with 43 per cent of these studies being from low-middle income countries.
“As we enter the third year of the pandemic, implementation of a global system or network for targeted, multi-pathogen, high-quality and standardised collaborative serosurveillance is a crucial next step to monitor the pandemic and contribute to preparedness for other emerging respiratory pathogens,” said the researchers.