Maternal COVID-19 Vaccination and Lactation Outcomes

The efficacy of coronavirus disease (COVID-19) vaccines available in the US is up to 95% against symptomatic COVID-19. However, pregnant and lactating individuals were excluded from initial clinical trials. COVID-19 vaccine trials are now underway in pregnant women in their second or third trimester but are not expected to conclude until 2022 or 2023, and evaluation of lactation outcomes is not planned. COVID-19 vaccines are highly effective, and mounting evidence suggests immunogenic protection for breastfed infants of mothers receiving COVID-19 vaccines. To date, there are no published studies on COVID-19 vaccine safety during pregnancy or lactation for breastfed infants, milk production and excretion, or other lactation-related outcomes. This lack of safety data threatens to undermine vaccination efforts in pregnant and lactating women. Traditional data sources used for post-licensure surveillance have limited relevance for lactation outcomes . Spontaneous reporting systems suffer from reporting bias due to their voluntary nature; their lack of a denominator of vaccinated lactating women precludes risk estimates. The CDC's V-Safe program, smart phone-based monitoring for vaccine side effects, does not capture lactation status. Ongoing health care claims-based surveillance studies also do not routinely capture lactation. Observational studies enrolling COVID-vaccinated lactating women rely primarily on self-reported outcomes and have limited generalizability. To address the need for comprehensive safety data, we propose a novel study of antenatal and postpartum COVID-19 vaccination and lactation-related outcomes in mother-infant pairs, including more than 11,000 breastfeeding dyads. We will use electronic health record data linked with state immunization data across four large health systems to study infant growth, infant heath care utilization, maternal mastitis, and breastfeeding status up to 7 months after delivery following maternal COVID-19 vaccination. Also, we will explore acute infant outcomes and abnormal infant developmental screens following maternal COVID-19 vaccination. We are uniquely positioned to overcome lack of information on lactation status and reporting and volunteer bias using routinely collected information on breastfeeding at well-child visits for a defined population. We will apply rigorous epidemiologic methods, including propensity score adjustment, to address confounding. With a focus on lactation, our study will complement other studies of COVID-19 vaccination in pregnancy and studies collecting milk samples from COVID-19-vaccinated volunteers. It will provide essential and currently unavailable evidence regarding lactation-related outcomes following perinatal COVID-19 vaccination. Findings supporting safety can reduce vaccine hesitancy, whereas results identifying a potential harm will be important for informing patient decision making. Furthermore, the novel approach and methods for studying lactation­ related outcomes developed through the proposed study can be adapted to efficiently evaluate the safety of drugs and vaccines currently recommended or being investigated for use in pregnant or postpartum women.