Serosurveillance provides estimates of antibody levels against infectious diseases and is widely used to measure population immunity due to past infection or vaccination. According to a new study led by the World Health Organization’s Unity Studies and SeroTracker, global Covid-19 infection rates are significantly higher than previously reported.
Usually, routine surveillance data underestimates infection rates and cannot reliably infer population immunity due to asymptomatic infections – which, in the case of Covid, are quite high – and uneven access to diagnostics. In order to determine the true rates of infection and indicators of population immunity against SARS-CoV-2 over time, the scientists conducted a systematic review and meta-analysis of seroprevalence studies published between January 2020 and May 2022. They analyzed seroprevalence by country and month in order to estimate regional and global seroprevalence over time, as well as seropositivity rates from infection versus infection or vaccination.
The analysis revealed that global seroprevalence has risen from 7.7 percent in June 2020 to 59.2 percent in September 2021, suggesting that nearly two-thirds of the global population had Covid antibodies from either infection or vaccination even before the emergence and spread of the highly contagious Omicron variants.
“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,” the authors explained.
“As we enter the third year of the Covid-19 pandemic, implementation of a global system or network for targeted, multi-pathogen, high-quality, and standardized collaborative serosurveillance is a crucial next step to monitor the Covid-19 pandemic and contribute to preparedness for other emerging respiratory pathogens,” they concluded.
The study is published in the journal PLoS Medicine.
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