Breastfeeding mothers who received either the Pfizer-BioNTech or Moderna vaccination reported the same local or systemic symptoms as previously reported in non-breastfeeding women, except in terms of milk supply.
The study was conducted by researchers at the University of California San Diego School of Medicine and published in the online edition of Breastfeeding Medicine.
Christina Chambers, PhD, MPH, professor of paediatrics at UC San Diego School of Medicine and professor in the Herbert Wertheim School of Public Health and Human Longevity Science, said: "Our study, along with previous research, suggests the Pfizer and Moderna vaccines are not red flags for breastfeeding mothers and their infants."
The results found that more than 85% of the 180 breastfeeding women in the study who received an mRNA COVID-19 vaccine reported temporary localised symptoms, such as pain, redness, swelling or itching at the injection site, and systemic side effects, including chills, muscle/body aches, fever and vomiting, with higher frequency after the second dose.
Additionally, after the second dose of vaccine, women who received the Moderna brand were significantly more likely to report symptoms. A small proportion of women after the first dose of either vaccine brand reported a reduction in milk supply, and significantly more women reported a reduction in milk supply following the second dose of Moderna.
“We want to emphasise that the reduction in milk supply was in a small subset of women and came back fully within 72 hours after vaccination. We also cannot be certain that the supply reduction was a side effect of the vaccine or another unknown factor,” said Chambers. “What we do know is that the vaccine is incredibly effective in providing protection from COVID-19, which has proven to be a devastating and serious virus with possible long-term side effects.”
Irritability and poor sleep were reported in some breastfed children, but no serious adverse events.
"We know the many benefits of breastfeeding. Breast milk provides an abundance of nutritional components to infants that provide many health benefits, from stronger immune systems to lower rates of obesity and other conditions and illnesses," said Chambers. "Our results should encourage lactating women to get the COVID-19 vaccine and to continue to breastfeed their infants. They do not have to choose one over the other. Both are critical."
The breastfeeding women recruited for the study enrolled into the Mommy's Milk Human Milk Research Biorepository at UC San Diego, which strives to understand the numerous benefits human milk offers at a molecular level and uses these findings to improve the health and development of all children.
The researchers noted that a limitation of the study was that symptoms post-vaccination were self-reported and suggested additional studies will be needed to see if the findings can be generalised to a larger population.
Study details
Maternal and Child Outcomes Reported by Breastfeeding Women Following Messenger RNA COVID-19 Vaccination
Kerri Bertrand, Gordon Honerkamp-Smith, Christina D. Chambers.
Published in Breastfeeding Medicine on 31 August 2021
Abstract
Introduction
Clinical trials for both the Pfizer-BioNTech BNT162b2 and Moderna messenger RNA (mRNA)-1273 COVID-19 vaccines demonstrated ability to prevent infection and severe disease, leading to emergency use authorisation by the US Food and Drug Administration in December 2020.
The American College of Obstetrics and Gynecology and The Society for Maternal Fetal Medicine have recommended that these mRNA vaccines be made available for lactating women. However, initial trials excluded breastfeeding women, leading to questions about their safety in this special population. One small study of 31 breastfeeding women who received an mRNA vaccine found that >60% reported vaccine-related side effects.
However, no data were provided on infant outcomes or milk supply. In addition, another small study of 84 breastfeeding women from Israel reported similar frequencies of vaccine-related symptoms following their first and second doses of the Pfizer-BioNTech vaccine (55% and 61%, respectively).
This study did not report any serious adverse events in the infants, but they did report that four infants had fevers and symptoms of upper respiratory infections during the study period following vaccination.
We sought to evaluate a larger sample of vaccinated breastfeeding women for vaccine-related symptoms and their breastfed children for any non-serious and serious adverse events.
Background
In December 2020, two novel messenger RNA (mRNA) vaccines for severe acute respiratory syndrome coronavirus-2 received emergency use authorisation from the U.S. Food and Drug Administration; however, the early trials excluded lactating women.
Methods
Breastfeeding women residing in the United States who received either of the two mRNA vaccines were enrolled into the Mommy's Milk Human Milk Research Biorepository at the University of California, San Diego. From December 14, 2020 to February 1, 2021, 180 women who received two doses of either mRNA vaccine were recruited into the study.
Results
Similar proportions of women reported any one or more symptoms following vaccination with either mRNA vaccine. In addition, the frequency by specific type of symptom did not differ by brand. However, following the second dose of vaccine, women who received the Moderna brand were significantly more likely to report symptoms. A small proportion of women following the first dose of either vaccine brand reported a reduction in milk supply, and significantly, more women reported a reduction in milk supply following the second dose of Moderna. Few infant events were reported for either vaccine brand following either dose, and no serious adverse events were reported.
Conclusions
These data are reassuring regarding the safety of vaccination in breastfeeding women and their breastfed children with either of the mRNA COVID-19 vaccines. Women who only received one dose of the vaccine were excluded from this analysis. Those who volunteered for the study were recruited into HMB through a variety of sources, including self-referral, through their health care providers, direct to consumer ads, and social media. Demographics, health history, vaccine brand, and maternal symptoms and child events were collected by maternal interview and questionnaire for seven days following each dose of the vaccine.
Results
Between 14 December 2020 and 1 February 1, 180 women who received both doses of either mRNA vaccine were enrolled. A total of 128 women (71.1%) received both doses of the Pfizer vaccine and 52 (28.9%) received both doses of the Moderna brand. Child age at enrollment averaged 7.47 months (standard deviation 5.44, range 0.09–27.45 months). More than one quarter of children (26.5%) were exclusively breastfed (defined as consumption of breast milk only—no formula or solid foods), almost half (45.9%) of children were breastfed eight or more times per day, and all women continued to breastfeed during the follow-up period.
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