The current study, published online in the journal Microbiology Spectrum, seeks to explore the link between this increase and the lack of antibodies against these pathogens in maternal blood and milk.
Passive immunity in breast milk, which contains antibodies to certain viruses due of maternal exposures, protects young newborns from respiratory viruses. Serious alarm has been raised about the decline in this protection as a result of the widespread social exclusion and other non-pharmaceutical treatments utilised during the coronavirus disease 2019 (COVID-19) pandemic.
A recent study that measured this protection and investigated the implications of declining antibody levels on newborn susceptibility to respiratory infections reported its findings in a new paper.
Infants who are just born and those who are a little older have very weak immune systems, making them more vulnerable to respiratory infections. A significant part of the baby’s defence comes from antibodies passed from the mother, first via the placenta and then via breast milk. These are mostly produced by plasma cells in the breast tissue and contain secretory immunoglobulin A (IgA), secretory immunoglobulin M (IgM), and immunoglobulin G (IgG).
While sIgA predominates, milk also contains IgG, which protects against respiratory viruses such the respiratory syncytial virus (RSV) and lowers the risk of acute infection in infants. Because of this, compared to newborns who are fed formula, breastfed infants have a lower risk of infant mortality and experience fewer respiratory illnesses. When the COVID-19 pandemic first emerged in the winter of 2019, there were severe limitations on mingling or congregating in public, closures of the majority of businesses and schools, and a ban on the majority of travel. As a result, RSV and flu detection rates were decreased by over 90%. But then came the summer surge, a peculiar occurrence mostly brought on by RSV.
Children’s wards and intensive care units were under a lot of strain as a result. The impact of COVID-19 on humoral immunity generation in response to the broad immunological activation brought on by this infection was another area of research.
The findings of the study indicated reduced breastmilk IgG titers against RSV, influenza, and the endemic human seasonal coronaviruses HCoV-OC43, HCoV-NL63, and HCoV-HKU1, in human milk, by about two-fold each, except for HCoV-OC43 at three-fold, and the last which showed only a small rise. Conversely, the serum levels of these antibodies increased by the same magnitude.
Notably, only anti-HCoV-OC43 IgG showed a decline at six months after the pandemic’s start in serum antibody levels in COVID-19-naive people. IgG levels were roughly 2 times greater in mothers with a history of COVID-19 than in mothers without such a history. IgA levels, meanwhile, were 2-4 times greater in each of these instances.
Researchers discovered that social hygiene practises had an impact on the development of passive immunity in breastfed newborns, which helped to explain the post-relaxation increase in baby hospitalizations. To plan for capacity issues after the distribution of the preventative measures and to foresee an increase in (severe) respiratory illnesses, it is crucial to be aware of the passive immunity of breastfed infants during the corona pandemic.
IgA levels did not change, although milk IgG levels did. This could be as a result of the latter’s short-lived first line of protection against the virus. It’s possible that the study’s late start caused the researchers to overlook the decline in IgA levels. IgG production, on the other hand, happens later in the immune system’s development and is high in the blood for months. Because they were not in circulation during the winter of 2018–19, there may have been no change in the IgG titers for HCoV-HKU1 and HCoV-229E. Additionally, the decreased amounts of antibodies in breastfeeding did not affect blood levels, which increased. This may indicate that milk antibody titers, rather than serum antibody levels, depend on recent exposures to respiratory viruses.
Respiratory viruses induce antibody production and the immune response to a variety of viruses, ruling out pathogen-specific effects. If so, the decreases in milk antibodies linked to lockdown and other restrictions may not be due to fewer viral infections, but rather to a general decline in immune system stimulation and milk antibody secretion. Due to possible cross-reactivity, mothers with a history of COVID-19 had greater antibody levels not only against the endemic seasonal coronaviruses but also against the flu virus and RSV. This might mean that these ladies were more susceptible to viral infections in general because of things like their jobs that required them to interact with the public. As an alternative, the SARS-CoV-2 might strengthen the immune system.
These findings may aid in creating better strategies to prevent future spikes in infant respiratory virus infections by safeguarding them in case lockdowns are ever required.
Parvathy Sukumaran 
