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To Better Protect Children from COVID-19, Children’s Hospital Los Angeles Researchers Follow How Immunity Develops Over Time

Children’s Hospital Los Angeles receives $4.2 million to study immunity in children and infants too young to vaccinate.

As new COVID variants have evolved, COVID-19 cases and hospitalizations of children under 5 have increased worldwide. Researchers have found that children are a key source of virus transmission in families and in the community—particularly since many are asymptomatic when they get infected.

“We are seeing children of all ages experiencing infection, with some requiring hospitalization,” says Pia Pannaraj, MD, MPH, an infectious disease specialist at Children’s Hospital Los Angeles. Dr. Pannaraj was awarded $4.2 million from the National Institutes of Health to study immunity in children who have received a COVID-19 mRNA vaccination, and in breastfeeding infants as young as 6 months of age.

While vaccination is the most effective way to prevent severe COVID infection and transmission among adults and school-aged children, no vaccine is currently available for infants under 6 months, who are at high risk for life-threatening complications from COVID-19. “This research will help us better understand the levels of immunity generated by vaccination, how that differs by age, or in the case of infants too young to vaccinate, what level of immunity is transferred through the antibodies in their mothers’ milk,” says Dr. Pannaraj, Director of the Pediatric Immunization Advancement Laboratory and Vice Chair of Research, Pediatrics at CHLA.

Immunity can differ by age

The immunity studies that have informed vaccine dosing and booster timing so far have mostly focused on adults. Dr. Pannaraj notes that as the immune systems of young children are still developing, they may respond to COVID-19 vaccination differently than adults.

The study will follow 560 children and their families over five years, measuring levels of immunity at different time points and in multiple ways. CHLA researchers will sample blood and the mucus lining of the upper respiratory passages of infants every three to six months to measure COVID-19 vaccine-induced antibodies. “When we're exposed to these viruses, the first exposure is usually in the nose or mouth, so we're also testing for antibodies in those areas,” says Dr. Pannaraj, who is also Associate Professor of Clinical Pediatrics and Molecular Microbiology and Immunology at the Keck School of Medicine of USC.

Breastmilk from vaccinated mothers may protect infants too young to be vaccinated from COVID-19 and other viruses, such as respiratory syncytial virus (RSV) or the flu. “We're studying children under 6 months because we're looking at maternal immune responses, so if mom got the vaccine, how does she pass on antibodies through the placenta?” says Dr. Pannaraj. “We are studying antibodies in breast milk to understand how immunity from vaccinated mothers is passed to infants.”

The researchers will also test a different type of immunity, called cellular immunity, by comparing T cells—a type of white blood cell that fights infection—in children with those of adults. T cells are a key marker of immune protection against breakthrough infection. “We will see what immunity is being produced and how long it lasts,” says Dr. Pannaraj. “Those are two of the main questions. The other big question is what protects you from getting the disease?”

Tracking family immunity over time

The researchers will combine data from the new study with samples from a previous COVID-19 vaccination and household transmission study of 1275 adults, children and pairs of breastfeeding mothers and their infants, launched in 2020 and which is still ongoing.

“Our goal was to study who got COVID-19, who didn’t, and why,” says Dr. Pannaraj. “We began enrolling families in the studies at the start of the COVID-19 pandemic. Now some of them are on the third or fourth COVID infection and it helps us to be able to understand what it is about those particular individuals or families that make them more susceptible to repeat infections.”

Dr. Pannaraj notes that earlier studies on COVID-19 lack important information on children and many are missing exposure histories. “It is important to follow the same individuals over an extended time to have the necessary time points,” says Dr. Pannaraj. “We can then predict what will be protective.”

Learn about research at the Pannaraj laboratory.