Since its identification in December of 2019, the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has infected over 550 million worldwide and caused over 6.3 million deaths. In addition to concerns regarding nursing mothers’ vulnerability to COVID-19 and whether they could transmit the infection to their babies during breastfeeding, researchers have also been interested in determining how breastfed infants may acquire immunity against SARS-CoV-2 from infected and/or vaccinated mothers.
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Maternal health and COVID-19
SARS-CoV-2 has been found to primarily infect cells through its interaction with the angiotensin-converting enzyme 2 (ACE2) receptor. During pregnancy, ACE2 receptor levels are upregulated, thus accounting for the relatively low blood pressure levels observed in many pregnant women. This increased ACE2 expression may account for why pregnant women are at a higher risk of developing serious complications from COVID-19.
Current evidence suggests that whilst the overall risk of severe illness is low in the general population, pregnant women are at an increased risk of experiencing severe illness with COVID-19 as compared to the normal population. Moreover, the risk of admission to the intensive care unit (ICU) in pregnant mothers infected with COVID-19 is about 1%, while the need for mechanical ventilation in this cohort is about 0.3%.
COVID-19-related complications in pregnancy are more likely to occur in the third trimester. The presence of certain maternal comorbidities such as obesity, chronic hypertension, diabetes mellitus, and being over the age of 40 can also increase the risk of severe disease in pregnant women.
Taken together, these factors have supported the vaccination of pregnant women against COVID-19. Although pregnant women were originally excluded from the initial COVID-19 vaccination studies, recent estimates suggest that about 18% of pregnant women have received at least one dose of a COVID-19 vaccine during pregnancy.
Prior to the emergence of several new SARS-CoV-2 variants of concern, COVID-19 messenger ribonucleic acid (mRNA) vaccines were associated with an efficacy of about 94% in both the general population and pregnant women. In addition to protecting women against COVID-19 and its complications during pregnancy, several studies have also confirmed that maternal vaccination against COVID-19 results in the transfer of SARS-CoV-2 antibodies to the fetus.
Can SARS-CoV-2 enter breastmilk?
One major concern that emerged early on in the pandemic surrounding maternal health is the possible transmission of SARS-CoV-2 through breast milk. Although several studies have confirmed the presence of viral RNA in the breast milk of infected mothers, current evidence does not indicate that the virus can be transmitted to the breastfeeding infant.
Thus, the United States Centers for Disease Control and Prevention (CDC) has stated that mothers with suspected or confirmed COVID-19 can safely continue to breastfeed. Nevertheless, the CDC recommends that infected mothers wash their hands before and after breastfeeding and expressing milk.
The potential for COVID-19 transmission through breast milk appears to be low. Nevertheless, it is crucial that infected mothers strictly abide by additional precautions if they are COVID-19 positive, as they can still transmit SARS-CoV-2 to their young babies through respiratory droplets and/or skin contact during breastfeeding. Therefore, breastfeeding mothers, as well as those who choose to express their milk with a pump, are advised to wear a mask anytime they are expressing milk, breastfeeding, or within six feet of their baby.
Breastfeeding during COVID-19
A 2021 The Lancet Global Health study investigating global public health approaches to mothers and breastfeeding infants concluded that current evidence supports mother-infant breastfeeding, even in COVID-19 positive mothers, whilst taking precautions to prevent respiratory spread. These recommendations have been further emphasized by the World Health Organization (WHO), which advises that both mothers and babies are kept together and that symptomatic mothers should wear a mask while expressing breastmilk.
The authors of this study also confirm that the survival benefits of breastfeeding outweigh the case fatality rate (CFR) for COVID-19-positive infants, which is very low.
Can breast milk help prevent COVID-19 in babies?
Human breast milk contains a wide range of soluble and cellular antimicrobial substances that contribute to the development and maturation of the immune system in infants.
Although some of the substances found in breast milk could benefit newborns during COVID-19, researchers maintain that there must be a balance between the protective inflammatory substances and those that modulate inflammation to protect the newborn against infection.
Some of the anti-inflammatory substances found in human breast milk include osteoprotegerin, which has been suggested to reduce the inflammatory response by preventing tumor necrosis factor (TNF)-induced inhibition of T-cells. Epidermal growth factor (EGF) has similar anti-inflammatory properties and can be found in higher concentrations in preterm milk as compared to full-term milk.
Another anti-inflammatory substance found in human breast milk is lactoferrin, which has been shown to reduce the production of proinflammatory cytokines. In fact, lactoferrin has been shown to prevent the binding between SARS-CoV-2 and its host cell receptors.
Breast milk from mothers who have previously been infected with SARS-CoV-2 typically provides a robust immunoglobulin A (IgA) dominant response. These antibodies appear to specifically react to the full SARS-CoV-2 spike protein, as well as its receptor-binding domain (RBD) and both S1 and S2 subunits. The anti-SARS-CoV-2 IgA obtained from the breast milk following maternal infection also appears to be reactive against the nucleocapsid protein.
As compared to breast milk obtained from mothers infected during pregnancy, vaccination against COVID-19 during pregnancy appears to produce a more uniform spike-specific IgG-dominant response that increases in concentrations after each subsequent vaccine dose. Anti-SARS-CoV-2-specific IgA has also been identified in the breast milk of vaccinated mothers, with its levels increasing five to seven days after receipt of the first vaccine dose.
The breast milk from both vaccinated and previously infected mothers also exhibits microneutralization activity against SARS-CoV-2.
Neonatal health and COVID-19
As compared to both older children and adults, COVID-19 is not common in neonates. Nevertheless, there remains a limited amount of information on the epidemiology of COVID-19 in this pediatric population.
In the United Kingdom, which was severely affected by the pandemic, a total of 66 babies who were infected with SARS-CoV-2 during the first wave required hospitalization. Both black and Asian babies in the U.K. are at an increased risk of contracting COVID-19, with an incidence of 18.0 and 15.2 per 10,000 live births, respectively. This is comparable to the incidence rate of 5.6 per 10,000 live births in the general neonatal population in the U.K.
SARS-CoV-2 infection is relatively rare in neonates; however, those who are diagnosed with COVID-19 will primarily experience mild acute symptoms. Comparatively, SARS-CoV-2 infection during pregnancy has the potential to impact the health of fetuses and neonates through various different mechanisms. Some of the potential neonate complications associated with COVID-19 during pregnancy include an increased risk of preterm birth and placental infection that can compromise nutrient and gas exchange to the fetus.
Overall, the short-term outcomes of infants who are born to mothers diagnosed with COVID-19 during pregnancy appear favorable. Nevertheless, about 25% of neonates born to mothers infected with SARS-CoV-2 are admitted to the neonatal intensive care unit (NICU). Pre-term infants, as well as those with certain comorbidities, have primarily accounted for the adverse neonatal outcomes reported in infants born to mothers infected during pregnancy.
As of June 2022, the United States Food and Drug Administration (FDA) has approved the administration of COVID-19 mRNA vaccines to children as young as six months of age. In addition to the protection conferred to infants through breastfeeding, current COVID-19 vaccines appear to offer an efficacy of up to 80% in children aged six months to four years, with or without a history of prior infection, following vaccination.
References
- Aiman, U., Sholehah, M., & Husein, M. (2021). Risk transmission through breastfeeding and antibody in COVID-19 mother. Gaceta Sanitaria 35; S524-S529. doi:10.1016.j.gaceta.2021.07.029.
- “Breastfeeding & Caring for Newborns” [Online]. Available from: https://www.cdc.gov/coronavirus/2019-ncov/if-you-are-sick/pregnancy-breastfeeding.html#breastfeeding.
- Magon, N., Prasad, S., Mahato, C., & Sharma, J. B. (2022). COVID-19 vaccine and pregnancy: A safety weapon against pandemic. Taiwanese Journal of Obestrics and Gynecology 61(2); 201-209. doi:10.1016/j.tjog.2022.02.005.
- Young, B E., Seppo, A., Diaz, N., et al. (2021). Association of Human Milk Antibody Induction, Persistance, and Neutralizing Capacity With SARS-CoV-2 Infection vs mRNA Vaccination. JAMA Pediatrics 176(2); 159-168. doi:10.1001/jamapediatrics.2021.4897.
- Ryan, L., Plotz, F. B., van den Hoogen, A., et al. (2022). Neonates and COVID-19: state of the art. Pediatric Research 91; 432-439. doi:10.1038/s41390-021-01875-y.
Further Reading
Genetic risk factors for long-COVID uncovered in a large multi-ethnic study