Of the three respiratory viruses Americans are facing this winter, two – the coronavirus and the flu – are well-known threats. The third respiratory syncytial virus, which has already sent thousands of babies to hospitals, is a mystery to many.
For pediatricians, however, RSV is all too familiar. It is a leading cause of infant mortality worldwide and particularly dangerous for babies born prematurely.
Worldwide, RSV led to approximately 3.6 million hospital admissions in 2019 and over 100,000 deaths in children under 5, mostly in poor countries.
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“Unfortunately he is one of those great killers that no one knows about,” said Dr. Keith Klugman, who heads the pneumonia program at the Bill & Melinda Gates Foundation.
“You survive RSV if you have access to treatment, respiratory support and oxygen,” he added. “In the absence of those, the children will die.”
The virus also poses particular risks for pregnant women, immunocompromised children and adults, and adults over the age of 65. There are no vaccines and treatments available. But after decades of stalled progress, more than 30 preventative options are on the horizon, nine of which are in an advanced stage of testing.
On Tuesday, Pfizer announced that its RSV vaccine showed 82% effectiveness against hospitalization among infants under 90 days of age and 69% among those under 6 months of age.
The vaccine hasn’t reached the Food and Drug Administration’s threshold for preventing doctor visits, but the company plans to submit its vaccine for approval later this year.
In October, GSK reported that its RSV vaccine was 83 percent effective against serious illness in adults over the age of 60. The vaccine is under review by regulatory agencies in Europe and Japan, and the FDA is expected to begin its review later this year.
Pandemic restrictions have kept RSV at bay mostly for the past couple of years. But this year, critically ill children with RSV are filling hospitals weeks earlier than usual. More of these young patients are sicker than those seen before the pandemic because they had developed poor immunity against RSV.
Babies who survive an RSV infection can suffer lung damage, making them more susceptible to pneumonia. Much of the damage comes from the consequences of the infection, rather than the infection itself.
Most older children and adults are exposed to RSV multiple times in their life, and the immunity they gain prevents serious illness, if not infection. Doctors have only recently begun testing for RSV in adults, leading to the realization that in some years RSV infections can compete with those caused by the flu.
“We just don’t appreciate it as much because diagnostics are not yet as available as they are for COVID or influenza,” said Dr. William Schaffner, an infectious disease physician at Vanderbilt University Medical Center in Nashville, Tennessee.
Among the elderly, RSV causes approximately 14,000 deaths per year. The recognition of the scale of the problem is partly responsible for the push by pharmaceutical companies to develop vaccines.
RSV was identified in the 1950s, and attempts to develop a vaccine began in the 1960s, but researchers have been thwarted for decades. The field was further set back when a candidate vaccine appeared to increase the risk of the virus.
A technical discovery in 2013 at the National Institutes of Health revived the field, allowing scientists to design powerful vaccines. In its trial, GSK’s vaccine was approximately 94% effective against serious illness in adults between the ages of 70 and 79 or in those with underlying medical conditions.
“We think we have a vaccine that can really be a very important solution to prevent serious respiratory diseases associated with RSV in the elderly,” said Dr. Phil Dormitzer, who leads vaccine development at GSK.
Several research groups are working on vaccines for young children. A group, led by Dr. Coleen Cunningham, chief pediatrician at Children’s Hospital of Orange County and chair of the Department of Pediatrics at the University of California, Irvine, is developing a nasal vaccine containing a weakened version of the virus for children 6 – 24 months of age.
“The upside is that it’s not a hit, so you don’t have to worry about needles,” Cunningham said. The vaccine would awaken antibodies in the nose, where the virus enters, rather than in the blood and thus could more effectively prevent infection.
Researchers are trying to find a balance where the virus is too weak to cause symptoms and yet strong enough to produce a robust immune response. The results so far are promising, Cunningham said.
In younger children, who are the most at risk, there is not enough time for vaccines to build sufficient immunity. An alternative is to give children a monoclonal antibody, a laboratory version of a powerful antidote to the virus, which can prevent infection.
One of these antibodies, Synagis, was approved in 1998 and is injected once a month into babies born after 32 weeks of gestation or less, or those who have heart or lung problems that exacerbate their risks. In studies, the antibody reduced hospitalization for RSV infection by 55%.
But Synagis is rarely used because it is prohibitive, Cunningham said.
Newer monoclonal antibodies can last longer and cost less. A committee of the European Medicines Agency has recommended the approval of a single dose of Beyfortus, manufactured by Sanofi and AstraZeneca, to protect children from RSV for an entire season.
Another alternative to protect children is to immunize pregnant women. The mother’s antibodies can cross the placenta to the fetus, research has shown, protecting the baby for the first few months after birth.
In the Pfizer study, approximately 7,400 pregnant women received a single dose of the experimental RSV vaccine or a placebo during the end of the second and third trimesters. The researchers monitored the health of the women for six months after giving birth and of the babies for at least a year.
The process spanned 18 countries and multiple RSV seasons in both the Northern and Southern Hemisphere. Klugman of the Gates Foundation said he hopes the vaccine “will spread very, very quickly” and will also be available in poor countries by 2024.
Some companies are testing the simultaneous administration of the RSV and flu vaccines and have found so far that neither seems to interfere with the other. Others are working to extend the duration of protection from an RSV vaccine.
The scale of RSV cases this year underscores the urgent need for vaccines and could serve to persuade parents to immunize their children once vaccines are available, experts said.
“Ironically, perhaps, if these outbreaks have a useful purpose, it will be to make RSV better known,” said Klugman, “so that when vaccines arrive, there will be an enthusiastic opportunity for women to protect. their children “.
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