There is good news on the horizon. This time next year there may be an RSV vaccine to protect newborns. Pfizer recently released the results of its Phase 3 clinical trial for a vaccine to be given to a pregnant person before giving birth, transferring immunity to the newborn. Pfizer says the vaccine has an efficacy of 81.8% for newborns in their first 90 days. Up to 6 months, the efficacy is still 69.4%. Pfizer plans to submit the vaccine to the FDA for approval by end of this year.
RSV Surging Across the U.S.
RSV is very easily transmissible. If a child in daycare is infected, the chances are high that other children will get sick. If a child brings the RSV home, family members will most likely also get sick, although some may have minimal symptoms. RSV season varies in different parts of the world and even in the United States. Certain areas, such as South Florida, have a much longer season. This year is proving to be a tough one with flu, RSV, colds, and COVID-19 all circulating at the same time. “A child can get infected with more than one virus at a time—and this can lead to the problems we have been seeing with very ill children, including ICU beds overflowing and pediatric hospitals in different parts of the USA having to open field hospitals or make contingency plans,” says Kunjana Mavunda, MD, MPH, a board-certified pediatric pulmonologist. It is unclear why RSV is surging currently. “This is happening about a month earlier than usual," addsZachary Rubin, MD, a double board-certified pediatric allergist. “COVID mitigation strategies such as wearing a mask and physical distancing helped reduce the spread of RSV as well.” He says since most people are not following those strategies, there are more people in close contact with each other, which may spread RSV faster. “It is exciting, however, that we may have an RSV vaccine available in the next 1-2 years,” says Dr. Rubin.
Vaccinating During Pregnancy To Prevent RSV in Newborns
The Pfizer bivalent RSV vaccine is still in trials with promising results in 7400 pregnant women. The drugmaker reports the vaccine is well tolerated with no safety concerns in adults and their newborns. The vaccine promises to provide protection to newborns through the pregnant parent and can be used for older adults as well. With high efficacy rates, Pfizer says the results of its phase 3 clinical trials show that the vaccine provides protection against severe illness and death. “This adenovirus vaccine shows strong promise to provide protection with a good safety profile in pregnant women and their infants,” says Suellen Hopfer, PhD, an assistant professor in the public health program at the University of California, Irvine. “A starting point is to recommend immunizing pregnant women and thereby conferring protection for their unborn child and providing protection when their child is born.” Dr. William Haseltine, Chair and President of ACCESS Health International, Inc, believes the vaccine is “badly needed and timely, given the current rising RSV infection rate. Clinical trials demonstrated that babies born to vaccinated mothers had greatly reduced rates of RSV infection.” Dr. Haseltine believes the best strategy to protect newborns is to protect the mother as newborns depend on maternal antibodies not their own. Older children 6 months and older could eventually be candidates for vaccination.
Why Newborns Are at High Risk for RSV
RSV mainly affects the lower respiratory airways. Since infants have very tiny airways compared to kids and adults, they are at higher risk of developing severe respiratory distress and possibly pneumonia. RSV is a unique virus. When someone gets infected with RSV, they do not develop long-term immunity. This means that one can get infected repeatedly. Almost all babies have had RSV at least once by the time they turn 2 years old. The most common symptoms are runny nose, fever, cough, and wheezing. But it can be as severe as bronchitis, bronchiolitis, pneumonia, and even death. Children in the high-risk group may need ICU admission and mechanical ventilation. “Some infants may have trouble eating or drinking,” says Zachary Rubin, MD, a double board-certified pediatric allergist. “However, other children may have signs of respiratory distress, including shortness of breath, flaring of the nostrils, straining of chest or stomach while breathing, turning blue around the lips, or short periods without breathing, also called apnea.” For most people, RSV is just a cold. They may have a runny nose, mild cough, or a sore throat. Patients with immune problems, young children, children with chronic medical problems, and the elderly tend to get more severe symptoms. “Unfortunately, after a severe RSV infection, the patient’s airway remains reactive, and they may have problems with recurrent wheezing,” says Dr. Mavunda. “When a patient needs hospitalization, it may take up to four weeks for the airway to become healthy. If an infant gets another respiratory viral illness such as influenza, parainfluenza, metapneumovirus, or even RSV again, the symptoms may be severe.” A baby’s immune system is also still developing. That means components of the immune system that are supposed to protect the airway may not be present yet. Dr. Mavunda says newborns have more severe symptoms because their airways are so small. “RSV attacks the respiratory mucosa. When [those] cells are damaged, the virus produces clumps of cells that then [close up] the airway. Also, the cilia which brush debris/mucus out of the airway are damaged,” he says. Airways of preemies are even smaller than those of newborns. This puts them at a higher risk of complications when infected with RSV. Children with congenital airway problems, chronic lung disease, complicated heart disease, neurologic disease, and some genetic disorders are also at a much higher risk of developing complications after an RSV infection.
The First RSV Vaccine Was a Failure
“A different kind of vaccine was developed and tested in the 1960s, which led to enhanced respiratory disease (ERD) in infants where the vaccine not only did not protect these children, it made them susceptible to having a more severe reaction to the virus if they were exposed,” says Dr. Hopfer. In fact, more children were hospitalized in the vaccinated group than those who were not vaccinated. Sadly, the deaths of two children are also attributed to this initial vaccine. Dr. Haseltine explains the difference between the vaccine in the 1960s and the ones being worked on now. “The structure of the original antigen did not induce protective antibodies,” he says. “Elegant work on the detailed structure of the protein revealed that it needed to be stabilized. The newly stabilized antigen induces protective antibodies whereas the previous one did not.”
Other RSV Vaccines in the Works
There are several vaccines in development, but the Pfizer one is the only one in a position ready to apply for approval. In March 2022, the New England Journal of Medicine published an article about an injection for newborns to prevent RSV called nirsevimab. The study found the injection was 74.5% effective in preventing RSV. There are other vaccines, particularly geared toward older people. Drugmakers GSK, Janssen, and Bavarian Nordic are working on those shots. Dr. Haseltine says they must be administered with powerful immune stimulants for an older population that is more resistant to vaccines. Such a vaccine could save many lives. Dr. Hopfer agrees that the efficacy data made available by Pfizer is very promising and provides an opportunity for protection for seniors, especially those who are vulnerable to RSV just as newborns and premature babies under 5 are.
