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Last winter, the world faced a “tripledemic,” a significant increase in COVID-19, flu, and respiratory syncytial virus (RSV) cases. RSV is a common respiratory virus that usually causes mild cold-like symptoms, but the virus can be life-threatening in young children and older adults.

In November 2022, RSV sent thousands of infants and children under 4 years old to the hospital at unprecedented levels in the U.S. This significantly strained the country’s hospital system, and some parents had to either travel or experience long waits to find a pediatric bed for their children. 

While last winter’s surge was particularly tough, each year the CDC reports that up to 160,000 older adults and 80,000 children younger than 5 years are hospitalized in the U.S. due to RSV infection.

The virus was discovered in the 1950s, and a vaccine has been in the works for decades with multiple candidates now approved by the FDA. In 2023 alone, multiple vaccines were approved for different populations:

“The reason why it was so difficult to develop is because when you develop vaccines, you got to find the right target that elicits a safe immune response that’s long lasting,” Dr. Zachary Rubin, an Illinois-based pediatrician specializing in allergy treatment and clinical immunology, tells PGN. “They finally found a target of where the immune system can basically create antibodies, these protein tags that can bind to the RSV virus.” 

Read on to find out more about RSV vaccines and their importance. 

Which RSV vaccines or treatments are currently approved or in the approval process? 

GSK’s single-dose vaccine for people 60 years and older, called Arexvy, was approved on May 3; and a single-dose vaccine for older adults from Pfizer (called Abrysvo) was approved on May 31. Abrysvo was also approved on August 21 for use in pregnant people, aiming to prevent lower respiratory tract disease (LRTD) and severe LRTD, which the virus can cause in infants from birth to 6 months.  

Additionally, on July 17, the FDA approved Beyfortus (nirsevimab), an RSV antibody treatment for newborns and infants developed by Sanofi and AstraZeneca. While not a vaccine, this treatment is a single dose given directly to newborns and infants in their first RSV season and to kids up to 2 years old who are vulnerable to severe RSV in their second season.

How do these vaccines work? 

The newly developed RSV vaccines use a form of a protein that’s part of the virus to elicit an immune response. “The RSV virus has something called viral fusion F protein that talks to your body cells to then enter into [them],” Rubin explains. “And so if you create a vaccine, that only gives that F protein, essentially, the immune system looks at that as a foreign substance, gobbles it up, and then creates antibodies that can bind to that F protein and neutralize it.”

Rubin offers an analogy to better understand: “So if you have a lock and a key, and you put gum on the key, then it’s not going to open the door. Think of the gum as the antibody that’s made by the vaccines’ immune response. And so that gunks up the ability for the virus to be able to hit the cells. It’s neutralized. It can’t work anymore.”

Why are RSV vaccines important now?

Experts believe last winter’s “tripledemic” happened because public health measures like isolating, mask-wearing, and social distancing during the pandemic kept us away from other viruses, which made our immune systems more vulnerable.

“This is something that I suspect is going to become more problematic each year, where we’re going to have a lot of people getting sick all at once, especially in the fall and the wintertime,” says Rubin. 

After decades in development, experts agree that RSV vaccines could help relieve the significant burden of RSV, including helping to prevent the millions of infant hospitalizations due to the virus around the world.

“If we’ve got an available vaccine that can reduce the risk of getting severely ill from one of these big [viruses], especially for young kids and [the] elderly, I would strongly encourage it,” Rubin adds. “Because we want to try to do whatever we can to keep kids and older adults healthy, safe, and out of the hospital.”

Are there any safety concerns?

The FDA’s approval process includes several safeguards to ensure vaccine safety before they reach the public. This includes receiving input from the Vaccines and Related Biological Products Advisory Committee (VRBPAC), made up of external experts in different science and public health areas. During the FDA’s recent VRBPAC meeting about the Pfizer vaccine in early March, some panel members said they were concerned about side effects reported during the vaccine’s trials, including one patient who developed Guillain-Barré syndrome (GBS) and another person who developed Miller Fisher syndrome, which is a type of GBS.

Despite this, the committee voted to recommend approval of both the Pfizer and GSK vaccines. Many experts agreed that the risk of severe illness from RSV is greater than any potential rare side effects from a vaccine.

“This type of phenomenon [GBS] can happen with infection; so when you get an infection, your immune system gets confused sometimes and creates an autoimmune phenomenon, meaning the immune system is attacking your normal healthy tissue,” Rubin explains. “The likelihood [of this] happening from a vaccine is far less compared to the actual infection itself. So we would say that the risks are not as great with a vaccine, that the benefits of the vaccine outweigh the risks of it, because you can prevent cases of Guillain-Barré syndrome by vaccination.” 

Pfizer and GSK told the New York Times that they will continue to monitor the vaccines’ safety once approved.

What does the availability of vaccines mean?

Approval of both the Pfizer and GSK vaccines for older adults in addition to the approval of Pfizer’s vaccine for pregnant people in August means that RSV vaccines are available before the start of the fall RSV and flu season.