Purpose: In this study, we examine the joint effects of stunting and socioeconomic status (SES) on COVID-19 serostatus in Brazil and whether these patterns vary by COVID-19 vaccine status. Methods: We use data from birth through the 7-year follow-up of the Pelotas 2015 birth cohort, including anthropometry, demographics, vaccination status, and COVID-19 antibody test results. We use linear regression models to examine the associations between SES (exposure) and stunting (effect modifier) on COVID-19 antibody titer among children who had not been vaccinated for COVID-19 (n=1,103) and among children who had been vaccinated (n=1,875). Results: All SES strata had a statistically identical probability of testing positive. While not statistically significant, stunted children who were unvaccinated tended to have lower COVID-19 titers (difference -0.10, 95% CI: -0.21,0.004) compared with children who were not stunted, and this difference was attenuated among stunted children who were vaccinated. Duration of school enrollment was associated with increased antibody titer, with each month being associated with a 0.17 unit higher increase in OD titer (95% CI: 0.15, 0.18). Conclusions: This result may suggest that stunted children have poorer immune responses to natural infection and thus lower immunity, but vaccination can overcome this deficit. Future recommendations include population-wide follow-up vaccination, particularly for stunted children. Given increasing antibody titer with a longer duration of school attendance, primary COVID-19 vaccination and potential boosters may be useful for children prior to school entry to reduce the risk of natural infection.

The authors have declared no competing interest.

This study did not receive any funding

I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained.

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The details of the IRB/oversight body that provided approval or exemption for the research described are given below:

The study protocol was approved by the Research Ethics Committee at the Federal University of Pelotas (School of Physical Education: 0-4 years, #26746414.5.0000.5313. Medical School: 6-7 years follow-up, #51789921.1.0000.5317). The childrens parents or legal representatives signed an informed consent form before each interview, including a statement authorizing the investigators to check their data on official health information systems, such as National Immunization Program Information System (NIP-IS) of the Brazilian Unified Health System (SUS for short, in Portuguese).

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All data produced in the present study are available upon reasonable request to the authors.