A small study from the University of California San Francisco shows the safety of COVID-19 vaccines in pregnant and lactating women by presenting evidence that mRNA from the mother is not transferred to the babies.

Vaccines such as those from Pfizer and Moderna are mRNA (messenger RNA) vaccines that teach the body how to generate the protein triggers an immune response without exposing the body to a form of the virus. Researchers examined breast milk samples from seven women who received the mRNA vaccines in the new small study. Test results show no traces of the vaccines used, providing the first direct data of vaccine safety during breastfeeding and is the latest addition to a growing body of study proving the safety of COVID-19 vaccines in relation to breastfeeding. The new study is important to address concerns and doubts, especially for expectant or lactating mothers who have either declined the vaccines or have discontinued breastfeeding out of vaccine safety concerns.

Researchers present their findings in the JAMA Pediatrics article "Evaluation of Messenger RNA From COVID-19 BTN162b2 and mRNA-1273 Vaccines in Human Milk," published earlier this month.

(Photo: Photo by NORBERTO DUARTE/AFP via Getty Images)
TOPSHOT - A woman breastfeeds her daughter while receiving a dose of the Moderna vaccine against COVID-19, at a vaccination center in Asuncion, on July 6, 2021.

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Allaying Fears of mRNA Transfer to Infants

Several studies have shown that mRNA vaccines have the ability to inhibit the transmission of SARS-CoV-2, the coronavirus that causes COVID-19. One study presented an evidence-based perspective on developing mRNA vaccines, published last April 2020 in the Medical Science Monitor journal. Another study, still a preprint accepted April 2021, examines the mRNA vaccines and their effect on COVID-19 transmission for long-term care facilities.

In the new UCSF study, researchers examined Pfizer and Moderna vaccines which both contain mRNA.

The World Health Organization has already discouraged stopping breastfeeding because of taking COVID-19 vaccines, and that even lactating mothers should take the vaccines. This is in line with the Academy of Breastfeeding Medicine saying that there is a minimal risk of materials from the vaccines entering breast tissues and being transferred to breast milk.

"The results strengthen current recommendations that the mRNA vaccines are safe in lactation, and that lactating individuals who receive the COVID vaccine should not stop breastfeeding," says Dr. Stephanie L. Gaw, a corresponding author in the study and an assistant professor of Maternal-Fetal Medicine at UCSF, in a news article from the university.

No Pfizer, Moderna Vaccines in the Mothers' Breast Milk

Yarden Golan, the lead author of the study and a postdoctoral fellow at UCSF, explains that they couldn't find the materials from the mRNA vaccines from the breast milk samples. Their findings should help boost public confidence in taking the vaccine.

The UCSF study ran from December 2020 to February 2021, with the mothers involved in the study having a mean age of 37.8 years old, and the infants receiving the breast milk were one to three months old. Researchers collected milk samples before getting the COVID-19 vaccines and other samples at different times 48 hours within which they got their shot.

Tests done on the after-vaccine samples showed no detectable level of the mRNA vaccines in any component of the milk, affirming vaccine safety regarding breastfeeding.


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