Immunizations that prevent respiratory syncytial virus (RSV) infections in infants continue to be effective three years after the medications were approved, according to two new studies.
In a study published in JAMA Network Open in mid-September, Canadian researchers found one of these immunizations, a set of lab-grown antibodies called nirsevimab, reduced emergency department visits related to RSV by 77%, hospitalizations by 79%, and intensive care unit admissions by 97%.
Another important finding from the analysis of Ontario data: About 97% of infants who tested positive for RSV had no underlying condition and were otherwise healthy.
“The results were dramatic,” said lead author Sarah Buchan, PhD, in a University of Calgary press release.
Nirsevimab is not a vaccine, which is a preventive that teaches the immune system to make protective antibodies over a period of two weeks. Instead, nirsevimab provides babies with a collection of ready-made antibodies that begin protecting them immediately.
Concerns about resistance
Researchers have worried that viruses in circulation could evolve ways to thwart these antibody medications and make them less effective at preventing infection.
Scientists who monitor RSV have identified genetic mutations in some strains that allow them to break through the biological blockades provided by nirsevimab, also known as Beyfortus.
An earlier, experimental RSV immunization failed in clinical trials because of a resistant strain.
In an article published in Nature the same week as the JAMA Network Open study, researchers from Seattle’s Fred Hutchinson Cancer Center and the University of Washington examined 60,000 genetic sequences from public databases of actual viruses circulating around the world to look for resistance mutations.
Resistance was rare. Fewer than 1% of RSV sequences contained mutations that make them resistant to nirsevimab or a second monoclonal antibody called clesrovimab, sold as Enflonsia.
A new era in RSV prevention
RSV can cause serious illness in children. Just a few years ago, RSV was the leading cause of hospitalization for babies in the first year of life, sending up to 80,000 children under five to the hospital each year.
Today there are several ways to protect babies.
In addition to antibody preparations given to babies, the Food and Drug Administration also has approved an RSV vaccine for pregnant people. Vaccinating people against RSV late in pregnancy protects babies from birth.
The new study results are good news for babies, the study authors say. Before the monoclonal antibodies were approved, RSV was the leading cause of hospitalization for babies in the first year of life.
“It's so incredible as a pediatrician, and as a mom, that we now have these prevention tools for RSV,” said first author Cassandra Simonich, MD, PhD, a research associate at Fred Hutchinson and a pediatric infectious diseases specialist at Seattle Children’s Hospital, in a Fred Hutchinson press release.
Simonich and her colleagues plan to continue analyzing strains of RSV circulating around the world to monitor whether resistant strains are becoming more common.
“We know these tools work really well in reducing severe RSV infections in babies,” Simonich said. “We want to ensure that these tools stay effective, and this study is a step toward ensuring our prevention methods keep working.”
Resistance a common problem in infectious disease
Although drugs can prevent and treat a number of infectious diseases, many become less effective over time, as bacteria and viruses find ways around them.
Many bacteria have evolved mutations that help them resist antibiotics, for example, making some bacterial infections difficult or impossible to treat.
And while pneumococcal vaccines save lives by preventing complications such as pneumonia, scientists have found bacterial strains that have mutated in ways that could make vaccines less effective.
CIDRAP reporter Laine Bergeson contributed to this story.
