COVID-Vaccinated Mothers More Likely to Have 'Functional Lactation Disorders': 'Journal of Korean Medical Science'

Functional lactation disorders are conditions that impact a mother's capacity to produce an adequate amount of milk for her infant.

A study published Monday in the Journal of Korean Medical Science evaluated the association between COVID-19 vaccination during pregnancy and lactation and reporting risk of adverse pregnancy or lactation outcomes.

The authors performed the study because “there is limited evidence on the safety of coronavirus disease 2019 (COVID-19) vaccination during pregnancy and lactation,” they write.

Their analysis identified 10,266 and 6,474 reports of “pregnancy and neonatal topics” associated with COVID-19 vaccines during pregnancy and lactation, respectively.

They found a “significant disproportionality” of what are called ‘functional lactation disorders’ associated with COVID-19 vaccines during pregnancy.

Functional lactation disorders are conditions that impact a mother’s capacity to produce an adequate amount of milk for her infant.

These functional lactation disorders “showed a significant disproportionate reporting for COVID-19 vaccines during lactation (aROR, 1.48 [95% CI, 1.21–1.79]),” the study states.

Specifically, the researchers found a significant disproportionate (increased) reporting association between COVID-19 vaccination during lactation and ‘mastitis,’ inflammation of the breast tissue that can sometimes involve an infection.

“We identified a significant disproportionality signal for mastitis associated with COVID-19 vaccine during lactation, with aROR (95% CI) of 2.76 (1.45–5.27),” the authors confirm.

“We found a significant disproportionate reporting association between COVID-19 vaccination during lactation and ‘functional lactation disorders’, specifically mastitis,” they write. “Continuous surveillance is warranted to confirm the safety of COVID-19 vaccine during pregnancy and lactation.”

Screenshot from jkms.org taken January 9, 2024

The authors note the majority of safety reports associated with COVID-19 vaccines during lactation were reported from women aged 18–44 years.

In their conclusion, they emphasize their “large pharmacovigilance study suggests that COVID-19 vaccination during lactation increased the risk of reporting functional lactation disorders, specifically mastitis.”