Researchers think they may have developed a vaccine that could protect babies from a virus that kills 200 U.S. children a year and puts 75,000 into the hospital.
Respiratory syncytial virus or RSV infects almost every child at some time, and usually causes little more than a bad cold. But in some babies, it causes a serious form of pneumonia that kills anywhere between 66,000 and 199,000 children globally every year.
There are vaccines against influenza, whooping cough and many different pneumonia-causing bacteria, but not against RSV.
"It's the next mountain to climb in terms of serious respiratory illness in children," Dr. Ruth Karron at Johns Hopkins University said in a statement.
"Part of the delay has been a delay in the recognition of the importance of RSV," she told NBC News. "We have made wonderful vaccines against other causes of pneumonia in children … As those vaccines were being developed there was frankly less attention paid to RSV."
And one vaccine tested back in the 1970s actually made children more vulnerable to infection later, which scared researchers off for a long time.
There is an immune treatment for very high risk babies called palivizumab and sold under the brand name Synagis by MedImmune. It's a so-called monoclonal antibody that helps the immune system fight RSV and when injected once a month can reduce a baby's risk of being hospitalized with RSV.
Now a team at the National Institutes of Health has genetically engineered the virus to make a preventive vaccine that should be safe and effective. They leave the virus "alive" but the genetic changes make it less likely to cause a dangerous infection, while at the same time making it more visible to the immune system.
Karron's team tested the vaccine in 15 adults and 45 babies. Some of the babies had already had an RSV infection while others had not.
They made a needle-free vaccine that could be dripped into the nose. Like the needle-free FluMist flu vaccine, the idea is to stimulate immune cells in the nose and respiratory tract first, and then throughout the body, they report in the journal Science Translational Medicine.
Almost all of the babies developed a strong antibody response to the vaccine, meaning their bodies produced immune system proteins that should neutralize a virus before it could cause an infection. To protect against RSV, people also need a second immune response in cells called T-cells, and the researchers have not been able to measure that yet in the babies.
The adults did not have an antibody response, but are likely to have already had natural RSV infections and to have overcome them. They were tested first for safety reasons.
"In order to induce an immune response, a live vaccine has to replicate," Karron said. "A vaccine that would replicate in adults would not be weak enough for children. We wouldn't go directly from animal studies into young children," she added.
"We don't anticipate that this would be a vaccine that's used in adults."
This vaccine is being developed in a three-way partnership with NIH and MedImuune, which makes FluMist, Karron said. It's one of several that groups are working on.
"Many RSV candidate vaccines are currently being explored, of which 12 are in clinical development as of this writing," wrote Dr. Anne Moscona, an expert in childhood respiratory disease at the Weill Cornell College of Medicine in New York.
It's likely that more than one type of RSV vaccine will be needed to conquer the disease, Moscona wrote in a commentary.