Nearly all children will catch the common wintertime respiratory infection known as RSV before they turn 2, sometimes with serious consequences, but for decades researchers have been unable to develop any means to prevent it.
Now a vaccine for Respiratory Syncytial Virus, as RSV is formally called, is showing promise in early trials at the Johns Hopkins University, giving researchers and doctors hope of stemming the leading cause of hospitization for children less than a year old. Every year, the virus sends an estimated 2 million children under age 5 to the doctor and 57,000 to the hospital, according to the U.S. Centers for Disease Control and Prevention.
"We really think it's a breakthrough in vaccination for infants and young children," said Dr. Ruth A. Karron, director of the Center for Immunization Research and a professor in the Bloomberg School of Public Health's department of international health.
Karron led the initial study of the vaccine, made from a weakened live virus. The goal was to make something strong enough to prevent the disease but weak enough that it didn't sicken young children.
The vaccine was created in a novel way, by deleting the gene for a particular protein that acts as something of a regulatory switch, controlling replication of RSV's genetic material, Karron said. When the protein is eliminated, the virus produces fewer copies of itself, lessening the chances it makes someone sick. Elimination of the switch also prompts the virus to produce larger amounts of other proteins that boost the immune response.
A crude vaccine was tested on children in the 1960s and when they were infected later with RSV it made them much sicker than if they hadn't been inoculated. For years after that, there was no progress on a vaccine, said Dr. Pedro Piedra, another vaccine researcher at the Baylor College of Medicine in Houston.
Piedra is working on a separate vaccine that would be administered to pregnant women to protect their infants in the first several months of life, much like the flu vaccine, which is generally only given directly to those 6 months and older.
Someday this combination of RSV vaccines could provide "blanket protection" from RSV from birth through childhood.
"I think everyone is encouraged when you see a promising vaccine work in target groups," Piedra said of the vaccine being tested at Hopkins. "We've been without a vaccine for over 50 years for this major respiratory disease of young children."
The vaccine wouldn't protect older people who already have been sickened by the virus because it wouldn't induce a strong enough response from their immune systems.
The new RSV vaccine was developed by the National Institutes of Health's Laboratory of Infectious Diseases in partnership with Gaithersburg-based MedImmune. The initial trial on humans was conducted at Johns Hopkins and results were published in Science Translational Medicine.
Karron said her team now will test a similar vaccine with the same gene deletion in larger groups of children, with the goal of having an approved preventive product in several years.
That was good news to Baltimore-area pediatricians who said they are in the middle of RSV season.
Dr. Susan Lipton, a pediatrician and infectious disease specialist at Sinai Hospital in Northwest Baltimore, said doctors' offices are packed with sniffling and coughing kids, many likely with RSV. They get the same advice as those with any respiratory virus: stay home, rest and drink plenty of fluids.
Lipton is most concerned about premature babies who are least equipped to handle the infection. She advises parents of infants to keep them away from crowds, cover their carriers with blankets, and make sure caregivers wash their hands regularly, especially during winter months.
"Be a dragon mommy and tell people not to kiss your babies," she said, noting that RSV is highly contagious.
When young children become sick, they are prone to bronchiolitis, an infection of the tiny airways to the lungs, and pneumonia, an infection in the lungs. Those complications lead to hospitalization in 2 percent to 3 percent of cases, Lipton said.
There is a medication that can lesson severity of symptoms for children most at risk, but it costs $1,000 a month and may not be covered by insurance. Doctors typically treat severe symptoms such as breathing problems with oxygen. They also provide intravenous fluids for those who don't or can't drink enough.
Dr. Rachel Plotnick, a pediatrician at the Greater Baltimore Medical Center in Towson, said a vaccine to prevent RSV and its complications "would be awesome."
The virus is not often fatal in the United States, although worldwide nearly 200,000 children under age 5 die annually, according to public health data.
Many parents don't know their children have RSV because they don't take them to the doctor. When they do, they are rarely tested.
Plotnick said she recognizes the wheezing sound of RSV when she hears it but unless the children are straining for air, she typically tells parents it's a virus and to treat it like any cold with fluids and pain relievers.
"I hear that breathing and I know," she said. "If they're young, there is a high risk of hospitalization, and no one wants their kids to be in the hospital. Babies with RSV look miserable. I would be happy if we could prevent it."
Even with a potential vaccine now on the horizon, it's hard to gauge if parents will be clamoring for it given heightened public debates over whether the many vaccines and immunizations babies and young children already receive early in life are warranted. Karron believes well-informed parents, especially those worried about their children becoming sick with RSV and needing hospitalization, will come around.
"There's education to be done because parents have kids who had RSV but were not told," she said. "I believe once parents understand the burden of this disease, they will welcome a vacinne."
She said she would not be suprised if the vaccine eventually became part of the schedule of vaccines for children recommended by various medical organizations and pediatric associations.
"This is something pediatricians will be very excited about because it is the leading cause of hospitalization among young children," Karron said. "My guess is it will be broadly recommended. There is a recognized unmet need for this vaccine."