Detection of SARS-CoV-2-specific mucosal antibodies in saliva following concomitant COVID-19 and influenza vaccination in the ComFluCOV trial.

The ComFluCOV trial randomized 679 participants to receive an age-appropriate influenza vaccine, or placebo, alongside their second COVID-19 vaccine. Concomitant administration was shown to be safe, and to preserve systemic immune responses to both vaccines. Here we report on a secondary outcome of the trial investigating SARS-CoV-2-specific mucosal antibody responses. Anti-spike IgG and IgA levels in saliva were measured with in-house ELISAs. Concomitant administration of an influenza vaccine did not affect salivary anti-spike IgG positivity rates to Pfizer/BioNTech BNT162b2 (99.1 cf. 95.6%), or AstraZeneca ChAdOx1 (67.8% cf. 64.9%), at 3-weeks post-vaccination relative to placebo. Furthermore, saliva IgG positively correlated with serum titres highlighting the potential utility of saliva for assessing differences in immunogenicity in future vaccine studies. Mucosal IgA was not detected in response to either COVID-19 vaccine, reinforcing the need for novel vaccines capable of inducing sterilising immunity or otherwise reducing transmission. The trial is registered as ISRCTN 14391248.
Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Rajeka Lazarus, Lucy Culliford, Sarah Baos, Rachel Todd, Russell Thirard, Rosie Harris, Alice Halliday, Holly Baum, Elizabeth Oliver, Benjamin Hitchings and Kapil Gupta report that financial support was provided by National Institute for Health Research. Rajeka Lazarus reports a relationship with AstraZeneca that includes: consulting or advisory and travel reimbursement. Rajeka Lazarus reports a relationship with Sanofi Pasteur that includes: consulting or advisory and travel reimbursement. Adam Finn reports a relationship with AstraZeneca that includes: funding grants. Adam Finn reports a relationship with Pfizer that includes: funding grants. Adam Finn reports a relationship with University of Oxford that includes: funding grants. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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