COVID-19 Vaccines

Many studies involving hundreds of women who received a SARS-CoV-2 (COVID-19) vaccine and their infants have been reported in the literature. No evidence suggests that receiving a vaccine against SARS-CoV-2 is harmful to either the nursing mother or the breastfed infant. Antibodies and T-cells that neutralize the SARS-CoV-2 virus appear in the milk after maternal vaccination.[1–5] Neutralizing capacity may increase even while antibody levels drop.[6] Nursing mothers experience minimal disruption of breastfeeding after vaccination, which may be related to having systemic symptoms.[7] A few mothers have reported to blue or blue-green discoloration of their milk.[8–12] A small percentage of breastfed infants may experience sleepiness, increased fussiness, fever, rash or self-limiting diarrhea, but no serious adverse effects have been reported. Numerous professional organizations and governmental health authorities recommend that COVID-19 vaccines be offered to those who are breastfeeding because the potential benefits of maternal vaccination during lactation outweigh any theoretical risks.[13–23] Only a small percentage of milk samples from women who received an mRNA vaccine (Comrinaty, Pfizer-BioNTech; Spikevax, Moderna) contain trace amounts of mRNA in some, but not all studies. mRNA has not been detected in the serum of any breastfed infants.[24–28] mRNA has an estimated serum half-life of 8 to 10 hours and is not detected in milk beyond 48 hours.[24,25,27,29] Moreover, the mRNA in milk is inactive in producing an immune response.[29] The new mRNA vaccine from Moderna (mNEXSPIKE) has not been studied in nursing mothers, but it contains less mRNA in each dose than Spikevax. The tiny amount of polyethylene glycol-2000 in Pfizer-BioNTech vaccine is not found in breastmilk or absorbed orally, so breastmilk PEG exposure from maternal immunization is not a concern.[30] Neither of the mRNA vaccines available in the US contains a preservative or adjuvant. Mothers who receive an mRNA vaccine have marked increases in milk antibodies that are similar to or higher than after a COVID-19 infection. Mothers who had a COVID-19 infection during pregnancy and received a vaccine had higher milk antibody levels than those who had either only an infection or two doses of vaccine during pregnancy.[31–36] Pregnancy may increase the anti-spike IgA and IgM antibodies in milk in a second pregnancy after prior vaccination of COVID-19 infection.[37] Milk IgA antibodies develop within 1 to 2 weeks after the first dose, with a loss in activity of 25 to 30% against the Alpha, Beta and Delta variants relative to the original strain. Milk IgG antibody levels are slower to develop after the first dose of an mRNA vaccine in lactating women, but increase after the second dose and persist in milk longer than IgA. In one study, mothers who had lactated for 24 months or longer had more than double the concentration of anti-viral IgG in their milk than mothers who had breastfed for less than 24 months.[38] Milk antibody levels persist for at least 6 to 8 months after vaccination. There appear to be no major differences in antibody response from the Pfizer-BioNTech and Moderna vaccines, although some studies found a better IgA response to the Moderna vaccine than the Pfizer-BioNTech vaccine.[39–42] Vaccine-induced clones are unique to individuals.[43] Milk antibody response against SARS CoV-2 following the adenovirus vector and inactivated vaccines appear to be considerably weaker and delayed compared to the mRNA vaccines, but are higher after the second dose than after one dose.[39,42,44–49] One study found the weakest breastmilk antibody response to the CanSino vaccine, compared to the Janssen and Pfizer-BioNTech vaccine.[47] Vaccination with an mRNA or adenovirus vaccine increases some proteins in milk, but far fewer and less inflammatory proteins and lipids than SARS-CoV-2 infection.[50] In addition to specific antibodies, several anti-inflammatory and antimicrobial proteins are found in higher concentrations in the milk of vaccinated or previously infected mothers.[51] A booster of the Pfizer-BioNTech or Moderna vaccine markedly increases IgG milk titers, including following an initial vector vaccine, but IgA titers are affected variably.[34,52–58] A vaccination interval of 3 to 6 weeks appears to generate a better milk antibody response than at 6 to 16 week intervals between vaccinations.[41] Women who had both a SARS-CoV-2 infection and vaccination with an adenovirus vector vaccine (Sputnik V [Gamaleya Institute] or ChAdOx1-S [Astra-Zeneca]) had higher IgA and IgG levels than women who received only a vector vaccine. Women vaccinated with BIBP-CorV (Sinopharm) had similar IgA levels in milk as with the vector vaccine, but lower milk IgG levels.[59] Some infants have anti-SARS-CoV-2 IgG in their saliva and stool samples after breastfeeding, and although some gastric and intestinal digestion occurs, titers appear sufficient to neutralize SARS-CoV-2.[60,61] Saliva antibodies potentially protect breastfed infants from infection by coating respiratory surfaces. No increase in serum anti-SARS-CoV-2 antibodies are found in infant serum after maternal vaccination unless mothers were vaccinated during pregnancy. The IgG in milk may offer protection to infants against coronaviruses that cause the common cold.[62]