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Antibodies against epitopes in S1 of SARS-2 coronavirus give the most accurate correlate of protection against infection. Measurement of those antibodies by neutralization or binding assays have predictive value. However, the protective functions of antibodies are multiple, including Fc effector functions. The role of cellular responses include CD4+ T cells and their augmentation of antibodies, as well as CD8+ T cells that control viral replication. More information is needed regarding mucosal responses.
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Goldblatt et al. (2022) studied this question.