Is COVID-19 Vaccines safe while breastfeeding?

Here is what NIH LactMed, the U.S. National Library of Medicine's authority on medicines and breastfeeding, reports about COVID-19 Vaccines. This is a summary of that source — not our own verdict.

Effects on the breastfed infant

In a cohort study of 180 women who received an mRNA vaccination (71% Pfizer, 29% Moderna) against SARS-CoV-2, some mothers reported side effects in their infants following vaccination. The most common events following the second dose were irritability (10.3% and 10.4% for Pfizer and Moderna, respectively), poor sleep (7.8% and 8.3% for Pfizer and Moderna, respectively), and significantly more drowsiness in children whose mothers received Moderna than Pfizer (6.4% and 0%, respectively).[ 10 ] It is not known if these side effects were caused by the vaccine. Twenty nursing mothers received 2 doses of an inactivated virus vaccine (CoronaVac, Sinovac). None of their breastfed infants had any adverse effects reported.[ 108 ] An on-line survey of 4455 nursing mothers who received either the Pfizer-BioNTech or Moderna vaccine found that 7.1% of mothers reported an adverse effect in their breastfed infant. The most frequent symptoms were increased sleepiness and increased fussiness, both at about 3% of infants, with the frequency greater after the second dose. Less frequently reported side effects included fever, rash, diarrhea, vomiting, changes in feeding frequency, and other miscellaneous symptoms. All were numerically, but not statistically more frequent after the second dose.[ 9 ] A study found that among the breastfed infants of 50 women who receive an mRNA vaccine against COVID-19 during pregnancy or lactation, none had any serious adverse effects. A few reports of minor sleep changes and gastrointestinal symptoms were reported after the first dose of vaccine, but 88% of women reported no infant side effects. None of the infants had any reported symptoms after the second dose.[ 32 ] A prospective study was performed in 88 lactating healthcare workers in Singapore given the Pfizer-BioNTech vaccine for COVID-19. No adverse events (fever, rash, cough, behavioral change, vomiting, or diarrhea) were reported by mothers among infants who were breastfed after maternal vacci

Effects on milk supply

In a cohort study of 180 women who received an mRNA vaccination (71% Pfizer, 29% Moderna) against SARS-CoV-2, some women reported a temporary reduction in milk supply. The percentages of women who reported a decrease in milk supply after the Pfizer vaccine was 7.3% and 8% after the first and second doses, respectively. The percentages of women who reported a decrease in milk supply after the Moderna vaccine was 8% and 23.4% after the first and second doses, respectively. The difference between the two vaccines was statistically significant after the second dose. In all cases, the milk supply returned to normal within 3 days. A few women reported an increase in milk supply after each dose. Five women reported a change in milk color to blue-green after a dose of vaccine.[ 10 ] In an on-line survey of 4455 nursing mothers who received either the Pfizer-BioNTech or Moderna vaccine, 3.9% reported an increase in milk production and 6% reported a decrease in milk production. The remainder of mothers reported no change in milk production.[ 9 ] A prospective study was performed in 88 lactating healthcare workers in Singapore given the Pfizer-BioNTech vaccine for COVID-19. No participant reported a change in milk supply. One reported a transient bluish-green tinge to her milk color after her first vaccine dose but not after her second dose.[ 11 ] A teratology information service in the Netherlands received reports of 194 women who experienced a decrease in milk supply after receiving the COVID-19 vaccine (89% Pfizer-BioNTech). The median time to the decrease was one day and the median duration was 4 days. Ten percent of women reported complete cessation of breastfeeding. These mothers had infant who were a median of 5.25 weeks old compared with 8 weeks for the entire cohort.[ 77 ] A survey of 1784 lactating women in Singapore who received either the Pfizer-BioNTech (79% of respondents), Moderna, Sinovac or Astra-Zeneca vaccine found that 5.6 to 14.4% of women reported either

Levels in milk

Several vaccines for COVID-19, have been developed. Vaccines available in the US (by Pfizer-BioNTech [Comirnaty] and Moderna [Spikevax]) are messenger RNA (mRNA) vaccines. Another mRNA vaccine is available in Europe (CureVac). Other vaccines (by Janssen-Johnson Johnson [now off the market], Astra-Zeneca [Covishield, Vaxzevria], Sputnik-V in Russia, and CanSino in China) are made using human and primate adenovirus vectors. A third type of vaccine available outside of the US is an inactivated whole-virus SARS-CoV-2 vaccine (by Bharat Biotech [Covaxin] in India, and Sinopharm and Sinovac in China). A fourth type, by Novavax (Nuvaxovid), contains a synthetic version of the S protein plus an adjuvant and a fifth synthetic protein subunit vaccine (Abdala) is produced in Cuba. In general, the Pfizer and Moderna vaccines have been studied the most extensively and have the most information on safety in nursing mothers.[ 70 ] mRNA vaccines are genetically engineered messenger RNA strands that encode for a portion of the SARS-CoV-2 S spike or S protein and are encapsulated within lipid nanoparticles. These nanoparticles are microscopic spherical-shaped mixtures of specialized fats, cholesterol, and polyethylene glycol that protect and deliver the mRNA strands to the recipient s cells after injection. Once inside the vaccine recipient s cells, mRNA is released, and its genetic code translated into viral S proteins. mRNA does not enter the cell nucleus or alter the cell s DNA. Those proteins are processed into peptides that are displayed on the cell surface, which then stimulates the antiviral immune response.[ 71 ] There is no plausible mechanism for intact, complete, functional viral S proteins to be distributed into the milk from the maternal circulation after immunization. Testing of the milk of mothers who received either the Pfizer-BioNTech or Moderna vaccine found little to no mRNA in their milk. Adenovirus vaccines . These vaccines are made from adenoviruses vectors that

Source: NIH LactMed (National Library of Medicine).

Educational summary of an authoritative source — not medical advice. Never start, stop, or change a medicine while breastfeeding without confirming with your doctor.