Lactating women can produce protective antibodies in their milk after vaccination, which has informed antenatal vaccination programs for diseases such as influenza and pertussis. However, whether SARS-CoV-2-specific antibodies are produced in human milk as a result of COVID-19 vaccination is still unclear. In this study, we show that lactating mothers who received the BNT162b2 vaccine secreted SARS-CoV-2-specific IgA and IgG antibodies into milk, with the most significant increase at 3–7 days post-dose 2. Virus-specific IgG titers were stable out to 4–6 weeks after dose 2. In contrast, SARS-CoV-2-specific IgA levels showed substantial decay. Vaccine mRNA was detected in few milk samples (maximum of 2 ng/ml), indicative of minimal transfer. Additionally, infants who consumed post-vaccination human milk had no reported adverse effects up to 28 days post-ingestion. Our results define the safety and efficacy profiles of the vaccine in this demographic and provide initial evidence for protective immunity conferred by milk-borne SARS-CoV-2-specific antibodies. Taken together, our study supports recommendations for uninterrupted breastfeeding subsequent to mRNA vaccination against COVID-19.

The paucity of information on longevity of vaccine-induced immune responses and uncertainty of the correlates of protection hinder the development of evidence-based COVID-19 vaccination policies for new birth cohorts. Here, to address these knowledge gaps, we conducted a cohort study of healthy 5–12-year-olds vaccinated with BNT162b2. We serially measured binding and neutralizing antibody titers (nAbs), spike-specific memory B cell (MBC) and spike-reactive T cell responses over 1 year. We found that children mounted antibody, MBC and T cell responses after two doses of BNT162b2, with higher antibody and T cell responses than adults 6 months after vaccination. A booster (third) dose only improved antibody titers without impacting MBC and T cell responses. Among children with hybrid immunity, nAbs and T cell responses were highest in those infected after two vaccine doses. Binding IgG titers, MBC and T cell responses were predictive, with T cells being the most important predictor of protection against symptomatic infection before hybrid immunity; nAbs only correlated with protection after hybrid immunity. The stable MBC and T cell responses over time suggest sustained protection against symptomatic SARS-CoV-2 infection, even when nAbs wane. Booster vaccinations do not confer additional immunological protection to healthy children.

Introduction: Severe Combined Immunodeficiency (SCID) is generally fatal if untreated; it predisposes to severe infections, including disseminated Bacille-Calmette-Guerin (BCG) disease from BCG vaccination at birth. However, delaying BCG vaccination can be detrimental to the population in tuberculosis-endemic regions. Early diagnosis of SCID through newborn screening followed by pre-emptive treatment with anti-mycobacterial therapy may be an alternative strategy to delaying routine BCG vaccination. We report the results of the first year of newborn SCID screening in Singapore while continuing routine BCG vaccination at birth. Method: Newborn screening using a T-cell receptor excision circle (TREC) assay was performed in dried blood spots received between 10 October 2019 to 9 October 2020 using the Enlite Neonatal TREC kit. Patients with low TREC had lymphocyte subset analysis and full blood count performed to determine the severity of lymphopenia and likelihood of SCID to guide further management. Results: Of the 35888 newborns screened in 1 year, no SCID cases were detected, while 13 cases of non-SCID T-cell lymphopenia (TCL) were picked up. Using a threshold for normal TREC to be >18 copies/μL, the retest rate was 0.1% and referral rate to immunologist was 0.04%. Initial low TREC correlated with low absolute lymphocyte counts (ALC), and subsequent normal ALC corresponded with increases in TREC, thus patients with normal first CD3+ T cell counts were considered to have transient idiopathic TCL instead of false positive results. 7/13 (54%) had secondary TCL (from sepsis, Trisomy 21 with hydrops and stoma losses or chylothorax, extreme prematurity, or partial DiGeorge Syndrome) and 6/13 (46%) had idiopathic TCL. No cases of SCID were diagnosed clinically in Singapore during this period and for 10 months after, indicating that no cases were missed by the screening program. 8/9 (89%) of term infants with abnormal TREC results received BCG vaccination within the first 6 days of life when TREC and ALC were low. No patients developed BCG complications after a median follow-up of 17 months. Conclusion: Newborn screening for SCID can be implemented while continuing routine BCG vaccination at birth. Patients with transient TCL and no underlying primary immunodeficiency are able to tolerate BCG vaccination.

Pre-approval clinical trials of the Pfizer/BioNTech messenger RNA COVID-19 vaccine, BNT162b2 did not include participants who were breastfeeding. Therefore, there is limited evidence about outcomes of breastfeeding mother–child dyads and effects on breastfeeding after vaccination. To determine: (1) solicited adverse effects (e.g., axillary lymphadenopathy, mastitis, and breast engorgement), which are unique to lactating individuals; and (2) systemic and local adverse effects of COVID-19 mRNA vaccine on mothers and potential effects on their breastfed infants. This was a prospective cohort study of lactating healthcare workers (N = 88) in Singapore who received two doses of BNT162b2 vaccination (Pfizer/BioNTech). The outcomes of mother–child dyads within 28 days after the second vaccine dose were determined through a participant-completed questionnaire. Minimal effects related to breastfeeding were reported by this cohort; three of 88 (3.4%) participants had mastitis, one (1.1%) participant experienced breast engorgement, five of 88 (5.7%) participants reported cervical or axillary lymphadenopathy. There was no change in human milk supply after vaccination. The most common side effect was pain/redness/swelling at the injection site, which was experienced by 57 (64.8%) participants. There were no serious adverse events of anaphylaxis or hospital admissions. There were no short-term adverse effects reported in the infants of 67 lactating participants who breastfed within 72 hr after BNT162b2 vaccination. BNT162b2 vaccination was well tolerated in lactating participants and was not associated with short-term adverse effects in their breastfed infants. The study protocol was registered at clinicaltrials.gov (NCT04802278).

Background: There was a considerably slower uptake among children despite the high COVID-19 vaccination uptake amongst adults and adolescents in Singapore. This was concerning as unvaccinated children are at risk of severe COVID-19 infections and a source and reservoir of infections. We sought to understand the impact of social media on parental vaccine hesitancy and to determine the risk factors associated with vaccine hesitancy.Methods: An electronic survey conducted from November 2021 to March 2022. Data on the demographic profiles of respondents and to classify them based on their vaccine hesitancy status. Data including the choice of social media used to obtain information on the COVID-19 pandemic, frequency of use were collected. Statistical significance was defined as p < 0.05.Results: Six hundred and twenty-eight parents participated. 66.9% of parents were not vaccine hesitant. About a third (27.2%) considered themselves somewhat vaccine hesitant. Fathers were more vaccine hesitant than mothers. Vaccine hesitancy was also associated with having a lower household income, unvaccinated parents, knowing someone with an adverse reaction to the Covid 19 vaccine and having a low level of trust in their child's doctor. There was no significant difference with high usage of social media between parents who were not vaccine hesitant vs. those who were vaccine hesitant. Despite high usage of social media, about two thirds (62.7%) of parents preferred print material to obtain COVID-19 related information. Parental trust in their child's doctor was the most significant factor in determining vaccine hesitancy amongst parents. When the variables of gender, household income status, vaccine status were further analysed with a multinomial logistic regression model, vaccine hesitancy in a parent could be predicted with a 70% accuracy, and non-vaccine hesitancy with a 92.4% accuracy.Conclusion: Newspapers and print media were the primary sources used in obtaining information on COVID-19 vaccine safety and efficacy, especially amongst parents with a higher household income. Healthcare providers should continue to establish rapport amongst parents, in particular the group with a lower household income to encourage higher paediatric COVID-19 vaccine uptake as well as correct COVID-19 related vaccine misconceptions or vaccine hesitancy, if present.