Of the three respiratory viruses Americans are grappling with this winter, two — the coronavirus (Covid-19) and the flu — are known threats. The third virus, RSV, which has already sent thousands of children to hospitals, is a mystery to many.
However, RSV is all too familiar to pediatricians, a leading cause of infant mortality worldwide, and particularly dangerous for babies born prematurely.
Worldwide, RSV led to about 3.6 million hospitalizations in 2019, and more than 100,000 deaths among children under five, most of them in poor countries, according to the New York Times.
“He’s, unfortunately, one of those big killers that nobody knows,” said Dr. Keith Klugman, who directs the pneumonia program at the Bill & Melinda Gates Foundation, referring to the virus.
“You survive RSV if you get care, breathing support, and oxygen,” he added. Without this, children will die.”
The virus also poses particular risks to pregnant women, children and adults with immunodeficiency, and adults over 65 years of age.
There are no vaccines and treatments for the disease, but after decades of faltering progress, more than 30 preventive options loom, nine of which are in advanced trials.
And Pfizer announced, on Tuesday, that its vaccine for RSV showed an efficacy of 82 percent against hospitalization among infants less than 90 days old, and 69 percent among those under six months of age.
The vaccine has not yet met the Food and Drug Administration’s approval threshold, but the company plans to submit its vaccine for approval before the end of the year.
In October, GSK reported that its RSV vaccine has an 83 percent effectiveness against serious infections in adults over the age of 60.
The vaccine is under review by regulatory agencies in Europe and Japan, and the US Food and Drug Administration is expected to begin reviewing it by the end of the year.
And pandemic restrictions have kept RSV mostly away from children for the past two years. But this year, children who are severely infected with RSV are filling hospitals weeks before the usual wave. And there are more of these young patients sicker than those seen before the pandemic because they have built up little immunity to RSV
Children who survive infection with the emerging coronavirus can develop damage to the lungs, which makes them more susceptible to pneumonia. Much of the damage is a consequence of the infection, not the infection itself.
Most older children and adults are exposed to RSV several times in their lives, and the immunity they acquire prevents severe illness, if not infection.
Among the elderly, RSV causes about 14,000 deaths annually.
RSV was diagnosed in the 1950s, and attempts to develop a vaccine began in the 1960s, but researchers’ efforts have been frustrated for decades. The field suffered a further setback when the candidate vaccine appeared to increase the risk of contracting the virus.
A technical discovery in 2013 at the National Institutes of Health revived the field, allowing scientists to design powerful vaccines.
At the time of its trial, the GSK vaccine had an efficacy of about 94 percent against severe disease in adults between the ages of 70 and 79 or those with underlying medical conditions.
Another alternative to protecting infants is to immunize pregnant women. Research has shown that the mother’s antibodies can cross the placenta to the fetus, protecting the baby during the first few months after birth.
In the Pfizer trial, about 7,400 pregnant women received a single dose of the experimental RSV vaccine or a placebo during the late second to third trimesters. Researchers tracked women’s health for six months after birth and infants for at least one year.
The trial involved 18 countries and multiple seasons of randomized trials in both the northern and southern hemispheres. Dr Klugman of the Gates Foundation said he hopes to “roll out a vaccine very, very quickly” and have it available even in poor countries by 2024.
Some companies are testing the simultaneous administration of RSV and influenza vaccines and so far have found that neither appears to interfere with the other. Others are working to extend protection from the coronavirus vaccine.
Experts said the scale of coronavirus cases this year underscores the urgent need for vaccines and may work to convince parents to vaccinate their children as soon as vaccines are available.