The surge of respiratory viruses that swept across North America last fall made respiratory syncytial virus (RSV) a household term – and a household fear for parents of young children.
Though it was new to many people, RSV is not a new virus. In fact, nearly every child contracts RSV by the time they’re two years old; half of children will have had it twice by then. For most children, an RSV infection is no more than a cold that may or may not merit a visit to a doctor. However, for as many as 3-4 million children worldwide every year, RSV results in hospitalization and, in very rare cases, death. Thus, considering that most every child gets RSV at least once, the challenge lies not in preventing RSV infection, but rather in preventing those that become severe. Research suggests that breastfeeding may be one way to overcome this challenge.
RSV infections, like many viruses, start in the nasal passage, causing runny nose, congestion and cough with or without fever. For many children, this will be the extent of their illness. For others, after a few days the virus migrates south into the lungs, resulting in a syndrome called bronchiolitis. When a child develops bronchiolitis, the tiny airways deep in the lungs become infiltrated with well-intentioned immune cells that cause swelling, narrowing an already narrow space as well as damaging the tissues necessary for the exchange of oxygen. This results in an inability to obtain sufficient oxygen that, depending on the degree of severity, can manifest as difficulty breathing, wheezing or full-out respiratory collapse requiring intubation and mechanical ventilation. There is no treatment for bronchiolitis. Puffers and steroids have no benefit. The only option is to treat the symptoms with supplemental oxygen until the infant’s immune system can clear the infection itself.
Many of the risk factors for severe RSV infection/bronchiolitis are not modifiable, including prematurity and congenital heart disease. However, one risk factor parents may have some control over is breastfeeding.
A meta-analysis published in 2003 in JAMA Pediatrics combining data from nine studies showed that exclusively breastfed infants were three times less likely to be hospitalized with a lower respiratory tract infection (like RSV) compared to formula-fed infants. An updated systematic review presented at the American Academy of Pediatrics conference in 2022 showed that exclusive breastfeeding not only decreased rates of hospitalization for respiratory infections but also decreased supplemental oxygen use in hospital.
Aviva Lowe, a pediatrician who practices breastfeeding medicine, says that in her clinical work she observes that “generally, breastfed babies have fewer infections and less severe infections,” adding “it’s not well known that breastfeeding brings with it a whole host of protective effects that are not well advertised … If there was a vaccine that we could give or a magic nasal spray that could do all these things, people would probably be jumping at it.”
The most obvious reason breastfeeding prevents severe RSV infection is the immune cells, antimicrobial proteins, probiotics, prebiotics and antibodies that breast milk contains. However, the direct transfer of protective immune factors is only part of the benefit. What’s even more important is breast milk’s ability to direct the development of the immature infant’s immune system. The mature adult immune system is comprised of an ensemble of characters, each playing a unique role. However, like the tiny humans who harbour them, an infant’s immune cells have yet to know who they will grow up to be and what role they will play. In the same way that life experiences and societal pressure influences who we become, our immune cells are similarly a product of their environment.
Breastfed infants were three times less likely to be hospitalized with RSV compared to formula-fed infants.
Regulatory T cells (Tregs) are little known members of the immune system whose destiny is uniquely influenced by their environment. Research has shown that breastfed infants have double the number of regulatory T cells compared to formula-fed infants. Tregs are also unique in their vocation. Instead of directly fighting infections, Tregs prevent immune cells from overreacting. Hence, as their name suggests, they “regulate” the immune system. This is important because an overzealous immune system is the hallmark of severe RSV infections and the cause of the aforementioned lung damage and airway narrowing. Animal studies have shown that when Tregs are artificially decreased, there is a significantly greater influx of excess immune cells into the lungs. Hence, breast milk is like a wise guidance counsellor who successfully inspires recruits to needed professions. And thankfully so because current strategies for preventing severe RSV infections are not without challenges.
Attempts to create a vaccine against RSV have been ongoing since the 1960s. However, considering that most children contract RSV twice by the time of their second birthday, it’s clear that from the perspective of the immune system, RSV is a very unmemorable virus, making it an ill-suited candidate for vaccine-based preventive approaches, at least so far. There is also an antiviral medication called Ribavirin that’s approved to treat RSV; however, it’s rarely used due to its questionable efficacy.
Currently, a drug called Palivizumab, given once monthly as an injection, is used to prevent severe RSV infection in the first year of life in at-risk children, including babies born prematurely (less than 29 weeks) as well as those with dysplasia of the lung, congenital heart disease and neuromuscular disorders. However, Palivizumab is expensive; in 2017 it cost the Canadian government $43 million to protect fewer than 7,000 preemies. This drug is an antibody derived from mice that binds the virus and blocks its “F subunit,” preventing it from fusing with our tissues and thus obliterating its uptake and infectivity. Interestingly, lactoferrin, an immune protein found in breast milk, has also been shown to prevent the uptake of RSV by directly binding its “F subunit.” Furthermore, lactoferrin has been shown to inhibit the growth of RSV at concentrations 10 times lower than what’s found in breast milk. Hence, even via identical mechanisms, breast milk is a cheaper way to prevent severe RSV infections.
That said, breastfeeding is not without challenges. Currently, in Canada 91 per cent of women initiate breastfeeding but only 34 per cent meet the World Health Organization’s recommendation to breastfeed exclusively for the first six months of life.
“Often our breastfeeding journeys are getting cut short due to misinformation,” says Laura Patterson, an International Board Certified Lactation Consultant who works in clinical settings and private practice. Access to these international board certified lactation consultants is not covered by OHIP and some health-care professionals may not know who to ask for help when patients present with breastfeeding concerns.
And it’s not just the technical issues that stand in the way of breastfeeding.
“Our culture, our society, our demands on parents and specifically those that identify as mothers are very high,” says Patterson. “It’s hard in the context of a culture that is very ‘bottle-feeding’ friendly and very ‘get-back-to-your-real-life’ friendly and is not giving parents the time to rest and learn their baby and just be with their baby.”
Science clearly demonstrates that breast milk helps the infant immune system develop properly. Thus, severe RSV infections/bronchiolitis is not the product of a virulent intruder that we are unable to defend against. Instead, it’s the earliest consequence of a sub-par immune system that is ill-equipped to organize and regulate itself.