Human Milk Antibodies Elicited by BNT162b2 Vaccination have reduced activity against SARS-CoV-2 Variants of Concern

We detected the presence of SARS-CoV-2 specific IgA against all major VOCs in milk out to 6 weeks after D2 of BNT162b2. These likely confer some protection to the breastfed infants, who are ineligible for vaccination and are at risk of severe COVID-19. However, we detected significantly reduced milk IgA binding to VOCs, including the globally dominant Delta variant, suggesting reduced protection for breastfeeding infants. Additionally, these antibodies were significantly reduced by as early as 4-6 weeks after D2. ### Competing Interest Statement The authors have declared no competing interest. ### Clinical Trial NCT04802278 ### Funding Statement J.M.L. received funding from KTP NUCMI and NUS Yong Loo Lin School of Medicine Pitch For Funds Grant to conduct this research. M.S.F.N. is a recipient of the Career Development Award from the Agency for Science, Technology and Research, Singapore. L.W.W. is a recipient of the National Medical Research Council Open Fund-Young Investigator Research Grant (Project ID: MOH-000545-00) from the Ministry of Health, Singapore. This study is funded by the SARS-CoV-2 antibody initiative (R-571-000-081-213) and Reimagine research fund (R-571-001-093-114). The authors wish to thank Miss Regena Chua Xin Yi (BsC) for helping with data collection and Dr Dimple Rajgor (PhD) for helping with preparing the manuscript for publication. We thank Prof Paul Anantharajah Tambyah for provision of funding and Dr Le Ye Lee (MRCPCH) for providing mentorship. No compensation was received for their roles. Last but not least, we are deeply grateful to all mothers who donated their time and precious gift of milk to science. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: National Healthcare Group Institutional Review Board (DSRB 2021/00095), Singapore All necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines and uploaded the relevant EQUATOR Network research reporting checklist(s) and other pertinent material as supplementary files, if applicable. Yes The data can be made available upon request.