Two respiratory syncytial virus (RSV) vaccines are coming to the market nearly 60 years after the National Institutes of Health first attempted to develop one. In May 2023, pharmaceutical companies GSK and Pfizer received approval from the U.S. Food and Drug Administration (FDA) for their RSV vaccines within weeks of each other. Both vaccines are currently available. Here’s what you need to know about RSV and the two new vaccines designed to protect against it.
What is RSV?
Respiratory syncytial virus, commonly referred to as just “RSV,” is an RNA virus that can cause cold-like symptoms and lung and respiratory tract infections. RSV has an A subtype and a B subtype. According to the Centers for Disease Control and Prevention (CDC), infection with RSV can cause symptoms such as:
- Reduced appetite.
- Runny nose.
In mild cases, RSV will resolve in about a week or two. But similar to influenza, RSV can be more serious for very young children and older adults. Every year an estimated 58,000 to 80,000 children under 5 and 60,000 to 160,000 older adults are hospitalized because of an RSV infection, according to the CDC. The CDC also says that an estimated 6,000 to 10,000 older adults die annually from RSV in the U.S.
According to Gregory A. Poland, M.D., director of the Mayo Vaccine Research Group, RSV can be particularly severe for older people because they’re more likely to also have other medical conditions like lung or heart disease.
The RSV vaccines
Enter the RSV vaccines: GSK’s Arexvy and Pfizer’s Abrysvo. Both vaccines have completed initial phase 3 trials and are now approved for people 60 years of age or older. Currently, the vaccines are approved for one dose because researchers are uncertain how long the vaccines will protect an individual, says Dr. Poland, but each should be available in time for the 2023 to 2024 viral season. Below we break down what you need to know about the trial and efficacy of each vaccine.
Arexvy: GSK’s RSV vaccine
Let’s start with GSK’s Arexvy. A study of 24,966 participants showed that Arexvy had an overall efficacy of 82.6% in preventing lower respiratory tract disease — such as pneumonia — caused by RSV. Its efficacy was 94.6% in preventing lower respiratory tract disease in older adults with one or more relevant medical conditions, such as a cardiorespiratory condition. The most common side effects reported by participants were:
- Pain at the injection site (60.9%).
- Fatigue (33.6%).
- Muscle aches and pains (28.9%).
- Headaches (27.2%).
The study also found a slight excess of abnormal heart rhythm (atrial fibrillation) cases. A separate study reported one case of Guillain-Barre syndrome, a condition in which the immune system attacks the nerves, in a vaccinated participant. Another study of Arexvy and a flu vaccine reported two cases of acute disseminated encephalomyelitis, a neurological disorder that induces swelling in the brain and spinal cord, one of which was fatal, in vaccinated participants.
Abrysvo: Pfizer’s RSV vaccine
Pfizer’s trial of 34,284 participants showed that Abrysvo had an 85.7% efficacy in preventing RSV lower respiratory tract disease with three or more symptoms. It dropped to 66.7% when looking at people with just two or more symptoms. The most common side effects reported were:
- Fatigue (15.5%).
- Headaches (12.8%).
- Pain at the injection site (10.5%).
- Muscle pain (10.1%).
There was one serious allergic reaction, one case of Guillain-Barre syndrome and one case of Miller Fisher syndrome — which is a variant of Guillain-Barre syndrome — reported among vaccinated participants.
According to Dr. Poland, the studies were too small in number to demonstrate if the vaccines reduced death rates from RSV. As with any vaccine, the large-scale release will show the vaccine’s full effects and patterns over time and across respiratory infection seasons.
Dr. Poland suggests that anyone with Guillain-Barre syndrome or another neuroinflammatory disorder speak with their doctor before getting the vaccine.
Vaccination for pregnant people
In August, the FDA also granted approval for Abrysvo to be used in pregnant people to protect infants from lower respiratory tract disease. Maternal immunization allows the vaccine’s antibodies to travel through the placenta and into the baby, says Dr. Poland.
A study of over 7,000 pregnant people showed that when the vaccine was given to those at 32 through 36 weeks gestational age, it was 91.1% effective in preventing severe lower respiratory tract disease in infants for three months and 76.5% effective for six months. Commonly reported side effects in pregnant people included:
- Pain at the injection site (40.6%).
- Headache (31.0%)
- Muscle pain (26.5%).
- Nausea (20.0%)
There were slightly higher rates of preterm births among those given Abrysvo compared to placebo, but there was not enough data to say whether the vaccine caused preterm birth. Thus, the vaccine is intended to be given to those at 32 through 36 weeks gestational age. The vaccinated group also saw slightly higher rates of pre-eclampsia in pregnant people, as well as low birth weight and jaundice in infants.
The long road to an RSV vaccine
Researchers tested an RSV vaccine decades ago, so why did it take so long for the first ones to get approved? Namely, the first attempts didn’t go so well. A vaccine for children started clinical trials during the winter of 1965 to 1966 in four locations around the United States. The National Institutes of Health (NIH) had based the vaccine’s development on polio and influenza vaccines without knowledge of RSV’s structure or function (something that is no longer an issue!). In trials, the vaccine inadvertently made children who had the vaccine sicker than those who didn’t, something known as a “vaccine-enhanced disease.” As Dr. Poland says, “That put a damper on the development of RSV vaccines for over 50 years.”
Will older adults take the RSV vaccine?
Dr. Poland expresses concerns over whether older adults will take the RSV vaccines when they become available.
“These two vaccines are coming at a time when there has never been more vaccine rejection, hesitancy and questioning of vaccines,” he says.
There’s no denying that vaccines are a polarizing subject in the U.S. The debate throughout the last few years over whether to take the COVID-19 vaccine is a prime example. As of May 2023, the CDC reported that 69.4% of people in the U.S. had completed the primary series of the COVID-19 vaccine. The numbers were significantly higher for individuals 65 and older, with 94.4% of people in that age range receiving the full course of the vaccine.
It is unclear whether this will translate to people 60 and over getting the RSV vaccine.
“I think any vaccine right now is contentious in the public’s mind,” says Dr. Poland. “I think it could be a hard sell — even though the benefits of the vaccine are clear in these large phase 3 clinical trials.”
Dr. Poland says physicians remain concerned about a repeat of last year — a “tridemic” of RSV, influenza and COVID-19.
“For the first time in history, we have good vaccines to protect against all three respiratory viruses and prevent the consequent illness, hospitalizations, disability and deaths due to these viruses in older adults,” he says.
If you have questions or hesitations about the RSV vaccine, talk to a member of your healthcare team.
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