In this preprint, not yet peer reviewed, led by SeroTracker, CITF-funded researchers and CITF Secretariat employees, the authors present an approach to help interpret serosurvey results and distinguish between infection-acquired and vaccine-induced immunity. Making the distinction between how infection and vaccine induced  immunity can help guide public health officials worldwide in their strategy for providing vaccines against COVID-19.

Before broad vaccination campaigns, serosurveys were relatively straightforward to interpret because SARS-CoV-2 antibodies were elicited primarily by symptomatic or asymptomatic infection. Since the rollout of vaccines, it is important to distinguish between antibodies from infection and antibodies from vaccination, or both. In countries using only spike (S) protein-targeting vaccines (Pfizer-BioNTech’s Comirnaty, Moderna’s Spikevax, and Oxford-AstraZeneca’s Vaxzevria), seropositivity for anti-nucleocapsid (N) antibodies indicates prior infection. Where vaccines that elicit both anti-S and anti-N seropositivity (e.g., inactivated or attenuated virus vaccines) are used, it is not possible to distinguish infection- and vaccine-induced immunity via serostatus alone.

SeroTracker is a global serosurveillance resource that provides information to help understand the true extent of the pandemic, identify groups at risk, monitor vaccine-induced immunity, and help chart an exit strategy from the pandemic.

Key points:

  • Serosurveys should include measurement of anti-S (and/or anti-RBD) and anti-N antibodies, as well as collecting information on vaccination history.
  • In countries with scarce vaccine supply, serosurveys could be used to inform efficient vaccine allocation.
  • In countries with high vaccine coverage, serosurveys can indicate the need for booster doses and help monitor the decay in antibodies.

Although prevalence of antibodies is increasing as vaccines are rolled out, appropriately adapted serosurveys can continue to provide crucial insight into population-level immunity.

Overall, researchers carrying out serosurveys should measure both antibody targets, together with vaccination history, to determine the prevalence and source of immunity. This will enable public health officials to monitor true infection rates, estimate infection fatality ratios (IFR), and asymptomatic infections.

Duarte N, Yanes-Lane M, Arora RK, Bobrovitz N, Liu M, Bego MG, Yan T, Cao C, Gurry C, Hankins CA, Cheng MP, Gingras AC, Mazer BD, Papenburg J, Langlois MA, Adapting serosurveys for the SARS-CoV-2 vaccine eraOpen Forum Infectious Diseases, 2021; ofab632, doi: https://doi.org/10.1093/ofid/ofab632