Sunday 10th October 2021

New data suggests breastfeeding women who have been infected with Covid-19 continue to secrete virus-neutralising antibodies into their milk for up to 10 months.

Besides emphasising the important role breastfeeding could play in helping to protect infants from the disease, researchers believe that such antibodies could be used to treat people with severe Covid-19, preventing their condition from getting worse.

Although young children are less at risk of developing severe Covid-19 than older people or those with underlying health conditions, approximately one in 10 infants under the age of one will require significant hospital care if they become infected.

"This is the breastfeeding population, so knowing if there are antibodies in the milk, how long they'll be protective after being infected, or which vaccine is going to give your baby the best antibody protection, is very important information, and will be relevant for a long time to come," said Dr Rebecca Powell at Mount Sinai hospital in New York, who led the research.

The antibodies in breast milk are somewhat different to the Immunoglobulin G (IgG) antibodies that predominate in blood and are triggered by vaccination - although some of these are also secreted into breast milk. The main antibody is Secretory Immunoglobulin A (IgA), which sticks to the lining of babies' respiratory and intestinal tracts, helping to block viruses and bacteria from entering their bodies.

Although researchers had previously detected antibodies against Sars-CoV-2 in breast milk, it was unclear whether they could neutralise the virus, or how long women continue to produce them after encountering coronavirus. To investigate, Powell and colleagues took breast milk samples from 75 women who had recovered from Covid-19, and found that 88% contained IgA antibodies. In most cases these were capable of neutralising Sars-CoV-2, meaning they could block infection.

Further measurements revealed that women continued to secrete these antibodies for up to 10 months. "It means that if you continue breastfeeding, you're still giving those antibodies in your milk," said Powell, who presented the results at the Global Breastfeeding and Lactation Symposium on 21 September.

She believes IgA antibodies extracted from breast milk could also be beneficial to adults with severe Covid-19. "It could be an incredible therapy, because Secretory IgA is meant to be in these mucosal areas, such as the lining of the respiratory tract, and it survives and functions very well there," Powell said. "You could imagine if it was used in a nebuliser-type treatment, it might be very effective during that window where the person has gotten quite sick, but they're not yet at the point of [being admitted to intensive care]."

Her team also investigated the transfer of coronavirus-specific antibodies into breast milk in 50 women after vaccination with either the Pfizer, Moderna, or Johnson & Johnson (J&J) jabs. All women injected with the Moderna vaccine, and 87% of those who received the Pfizer vaccine had coronavirus-specific IgG antibodies in their milk, while 71% and 51% respectively had virus-specific IgA antibodies. For the J&J vaccine, only 38% of women had IgG antibodies and 23% had IgA antibodies against coronavirus in their milk.

Powell said: "We know that the level of antibodies produced by RNA vaccines is extremely high compared to other vaccines. You don't necessarily need that much antibody to protect you from infection, but the milk effect really depends on there being a lot of antibody in your blood that's transferring into your milk. Because there's a lower level stimulated by the J&J vaccine (a viral vector vaccine), that's probably why there's very low levels in the milk."

The team is now investigating the antibody response in breast milk triggered by the AstraZeneca vaccine.

News and photos from The Guardian

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