Bronchiolitis : An RSV vaccine that may protect against the chest infection shows promise in mice

An experimental vaccine warded off the respiratory syncytial virus, the most common cause of the chest infection bronchiolitis, in newborn mice

By Carissa Wong

An experimental vaccine has shown promise at protecting mice from the respiratory syncytial virus (RSV), the pathogen that most commonly causes the chest infection bronchiolitis in young children.

“Over years of work, we showed that this vaccine… was the magic sauce to unlock infant immunity [in mice],” says Ofer Levy at Boston Children’s Hospital in Massachusetts.

Almost all children catch RSV before they turn 2 years old. In both children and adults, most develop cold-like symptoms. But some children are more vulnerable to RSV’s complications, including those who were born prematurely or those with a lung, heart or immune condition.

Worldwide, RSV is estimated to cause more than 59,000 deaths each year in children under 5, with no drugs approved to treat the bronchiolitis it causes and no vaccines to ward off RSV in the first place.

In an effort to fill this vaccine need, Levy and Simon van Haren, also at Boston Children’s Hospital, and their colleagues developed a vaccine that contains key immune-stimulating molecules, called adjuvants, along with a fragment of a protein that RSV uses to enter cells, called F protein.

Twelve newborn mice, aged 4 to 7 days old, were injected with the vaccine or a saline solution. The mice were then exposed to RSV seven weeks later.

About two weeks after RSV exposure, the virus was found in the lungs of the mice that were given saline, but not in the vaccinated mice. The concentration of RSV in the noses of the vaccinated mice was also 100 times lower than in the control mice, suggesting that the virus had more effectively infected the upper airways of the unvaccinated mice.

The researchers also looked at the vaccinated mice’s immune response to RSV.

“The adjuvant combination robustly enhanced antibody and useful T-cell responses and indicated protection against RSV infection in infant mice,” says Levy.

When tested in human blood cells taken from newborns, the vaccine also generated a favourable immune response.

One limitation of the study is that the mice were adults by the time the experiment ended. In people, RSV causes bronchiolitis in young children. The immune response of the mice at several weeks old, when they were adults, may therefore not apply to young children.

The researchers hope to next test the vaccine in non-human primates and then people.

“Humans and mice are very different systems, though they do have many similarities… If everything goes smoothly, we’d hope to start trials in people within five years,” says Levy.

Journal reference: Nature Communications, DOI: https://doi.org/10.1038/s41467-022-31709-2