After the second dose, one or more side effects were reported by 81% of the participants. of the reference lists of included articles. Data concerning country, study period, number of participants, type of applied vaccine, time points of sampling and outcome measures were collected from the selected manuscripts. The data are summarized and synthesized in a descriptive way. Results 30 manuscripts were included in this review. Data on safety of COVID-19 vaccination during lactation indicate no severe vaccine-related local and systemic reactions, both after first and second dose, neither in the mother nor the nursing child. No significant amount of vaccine components seems to appear in breast milk. Milk supply data after vaccination are inconclusive as AP24534 (Ponatinib) there are no quantitative data available. Some women however observe a temporary increase or reduction AP24534 (Ponatinib) in milk supply, without long-term effects. All prospective cohort studies demonstrated the presence of SARS-CoV-2-specific antibodies in breast milk of nursing mothers vaccinated against SARS-CoV-2. Nearly all studies were conducted with mRNA vaccines. Conclusion There is evidence that the administration of a COVID-19 vaccine is safe and poses no additional risk to the breastfeeding woman or the breastfed baby. After vaccination of the mother during the lactation period, antibodies appear in the milk, which could protect the infant against COVID-19. Professional associations and government health authorities should AP24534 (Ponatinib) therefore recommend offering COVID-19 vaccines to breastfeeding women, as the potential benefits of maternal AP24534 (Ponatinib) vaccination while breastfeeding outweigh PECAM1 the risks. the placenta and breast AP24534 (Ponatinib) milk, since they are born with an immature immune system. The role of immunoglobulin G (IgG) transferred the placenta is well established, but less is known about the transfer of antibodies and the mechanisms by which these antibodies provide protection to the neonate breast milk (15). It is therefore plausible that the immune response triggered by vaccinating lactating women may be different from the general population. The conclusions will contribute to the knowledge on COVID-19 vaccination and the results will benefit the population with respect to public health. Methods Study Design and Searches We searched Ovid Embase Classic+Embase, PubMed and BioMed Central for articles published between December 1st 2020 and December 31st 2021. The search strategy contained terms and combinations related to COVID-19 vaccination during lactation, including the MeSH terms COVID-19, COVID-19 Vaccines, SARS-CoV-2, Lactation, Breast Feeding, Pregnancy and Postpartum Period. The final literature search was performed on the 31st of December 2021. The database search was completed with a manual search of the reference lists of included articles (i.e. snowballing). The quality of reporting was supported by the use of the PRISMA guidelines (16). The detailed overview of the search strategy is provided in Appendix 1 . Eligibility Criteria and Study Selection Manuscripts were eligible for inclusion if (1) study participants were women vaccinated with a COVID-19 vaccine during the lactation period and (2) the results reported on the safety of vaccination during lactation OR on the excretion of COVID-19 vaccine components in breast milk OR the excretion of immunological factors in breast milk after COVID-19 vaccination OR on the impact of COVID-19 vaccination on the breast milk production. Manuscripts published in English, French, Dutch, German or Spanish were included. Studies that focused on women with specific pathologies (e.g. transplant patients) were excluded. JM and ET independently screened titles, abstracts and full-texts of the retrieved manuscripts for eligibility. Each manuscript showing uncertainty regarding inclusion criteria was discussed with the other authors until consensus about inclusion. Data Collection, Synthesis and Analysis Data concerning country, study period, number of participants, type of applied vaccine, time points of sampling and outcome measures were collected from the selected manuscripts. The datasets were summarized and synthesized in a.