This is a summary, written by members of the CITF Secretariat, of:

Pluss O., Campbell H., Pezzi L., Morales I., Roell Y., Quandelacy T. M., Arora R. H., Boucher E., Lamb M. M., Chu M., Bärnighausen T., Jaenisch T. Limitations introduced by a low participation rate of SARS-CoV-2 seroprevalence data. International Journal of Epidemiology (2022). doi:

The results and/or conclusions contained in the research do not necessarily reflect the views of all CITF members

In a study published in the International Journal of Epidemiology, the CITF-funded SeroTracker team, including Dr. Rahul Arora (University of Calgary), contributed to showing that only 70% of individuals invited to participate in seroprevalence studies actually enrolled. This is problematic because the lower the participation rate, the more limited the representativeness of the results. Moreover, due to a lack of standardization, making valid comparisons between seroprevalence studies remains a challenge.

Key findings:

  • Participation rates range from 0.43% to 96.38% across seroprevalence studies around the world, with a median of 70%.
  • Only about half of the studies showed participation rates above 60%.
  • Rates of participation were higher among studies using a convenience sampling strategy, but these methods are more prone to bias. Indeed, these studies recruit participants because they are the easiest to access for researchers (reasons may be geographical proximity, availability, or willingness to participate). Random selection strategies, on the other hand, provide more valid results but are more resource intensive.
  • 61% of seroprevalence studies did not report participation rates, which makes it difficult to truly assess the representativeness of the seroprevalence estimates that they report.

For the purposes of this study, participation rate is defined as the number of respondents who have provided a valid serological sample divided by the initial number of people invited to participate in the study. Reasons for not participating in a study range from not receiving the invitation, not agreeing to participate, or not providing a blood sample.

While many seroprevalence studies have been conducted across the globe, many during the first year of the COVID-19 pandemic, comparability between seroprevalence estimates remains a challenge. Standardized definitions and systematic reporting of participation rates would be a first step in reducing sources of heterogeneity between studies.

This study used data compiled by SeroTracker. Analysis was restricted to SARS-CoV-2 seroprevalence studies in the general population. A total of 90 papers from December 1, 2019 to March 10, 2021 were included. Only 35 of them (39%) provided the information needed to calculate the participation rate.