How mothers protect babies from chickenpox

Mothers with a past history of chickenpox infection may transmit chickenpox viral DNA to their babies during pregnancy, thereby stimulating their immunity against this infection, says a new study by medical researchers of St. Stephen’s Hospital and the National Institute of Immunology (NII), New Delhi. The study included 350 mothers and their newborn babies. This mother-to-child transfer of viral DNA may be responsible for the long-lasting protection against serious chickenpox infection seen during childhood, according to its findings reported in the journal “Viral Immunology”.

The findings will revolutionise the current understanding of how babies are protected against infections such as chickenpox in childhood, say the researchers. Chickenpox reactivation after surgical stress is known. Scientists have demonstrated that the stress of space travel can induce subclinical reactivation of chickenpox in astronauts.

“Subclinical reactivation of chickenpox, induced by the stress of pregnancy, is being reported for the first time,” say the authors. The present understanding is that mothers provide their babies protection against a variety of common infections by transferring ready-made antibodies to them. The protection to the baby lasts for 12 to 15 months. If the baby encounters the infection while partially protected by maternal antibodies, the illness is mild. The baby then develops his/her own long-lasting immunity.

Jacob Puliyel of St. Stephen’s Hospital and his colleagues suggest that in the case of chickenpox, mothers develop subclinical viremia and the viral DNA is transferred to their babies. It is likely that in such cases, antibodies are developed actively in the foetus. “Babies develop more long-lasting active immunity with the transfer of chickenpox DNA from mothers—more than the short-term passive protection provided by the transfer of ready-made antibodies,” say the authors.

In the absence of vaccines, chickenpox spreads easily in the population and repeated exposure to the virus acts like booster doses. The high antibody levels—much higher than that after vaccination—are passed on to babies. Vaccination, on the other hand, will reduce person-to-person spread of natural disease and the antibody titres are not boosted, and so there is little protection provided to the next generation. According to the authors, the “chickenpox parties” to get children exposed to others with chickenpox was not a bad idea, as they get naturally infected in childhood, when the disease is typically mild. They found that antibody levels against chickenpox in newborn babies were often higher than that in mothers, suggesting that the antibody was actively transported to the baby.