Serosurvey in Sierra Leone Points to Underreporting of Cases, Risk of New Variants

A COVID-19 antibody survey conducted in Sierra Leone is the first nationally representative investigation of COVID-19 seroprevalence conducted on the African continent and presents evidence of large-scale underreporting of cases and low vaccination rates. Results of the study, based on data collected in March 2021, are published in BMJ Global Health.

“Our findings remind us that there still may be significant under-reporting of COVID-19 in various countries throughout the region,” said Eugene T. Richardson, MD, PhD, Divisions of Infectious Diseases and Global Health Equity, Brigham and Women’s Hospital, and corresponding author of the paper in BMJ Global Health. “There are still likely significant portions of the population that don’t have acquired immunity to infection with earlier SARS-CoV-2 variants, and there are still very low vaccination rates in the region. This means populations may be at higher risk for severe illness if infected with the Omicron variant.”

The researchers found:

  • Underreporting: The team’s findings indicate that more than 200,000 people had been previously infected, which was 43 times higher than the reported number of cases.
  • Low acquired immunity: As of March 2021, 2.6 percent of the population had been previously infected, with urban settings having double the rate of rural settings.
  • Low vaccination rates: As of December 8, 2021, less than 5 percent of Sierra Leoneans had been fully vaccinated and, at the current vaccination rate, it will take more than several years to vaccinate the whole population.

Together, these findings are cause for grave concern, according to Richardson.

“We are calling for more rapid vaccine deployments in countries like Sierra Leone as part of global vaccine justice, including support for intellectual property waivers and technology transfers,” he said. “We hope this study also encourages other nations to conduct serosurveys since they can provide data that are vital to understanding the pandemic’s progression.”

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