What’s in the RSV vaccine, its side effects and when you can get one

Models created by 3D printing of the pre-fusion and post-fusion form of a protein from the respiratory syncytial virus, or RSV, at the Faulkner Nanoscience and Technology Building at the University of Texas at Austin on March 31, 2022. (Photo for The Washington Post by Montinique Monroe)

The first vaccine to prevent the respiratory disease caused by RSV was approved this week by U.S. regulators for use in adults 60 and older.

The shot, developed by pharmaceutical giant GSK, will be rolled out ahead of the fall and winter RSV season, when transmission peaks. Most people are infected by respiratory syncytial virus repeatedly over a lifetime and experience only a mild cold, but babies and vulnerable older adults can become severely ill.

Depending on the season, 60,000 to 120,000 older adults are hospitalized in the United States with RSV each year, and 6,000 to 10,000 die, according to the Centers for Disease Control and Prevention. In an earnings presentation released last week, GSK said it has “millions of [vaccine] doses ready to be shipped.”

Here’s what you need to know about the newly approved vaccine, from how it works to what happens next.

What’s in the RSV vaccine?

The new vaccine, called Arexvy, contains a harmless version of a protein found on the outside of the virus. That viral protein shape-shifts after it infects a person’s cells, so the vaccine uses a version that has been locked into a lollipop shape - in effect, training the immune system to block the virus before it can enter.

The vaccine also contains an adjuvant, an ingredient used to rev up the immune system. Arexvy uses the same adjuvant that’s in GSK’s shingles shot, Shingrix, but half of the dose.

Does this vaccine use a new technology?

No. This is a protein-based vaccine, similar to ones that are used against other diseases, including a hepatitis B vaccine, a shingles shot and an influenza vaccine. The protein in the vaccine is produced by cells in a laboratory.

How effective is the new RSV vaccine?

RSV causes trouble when it gets deep into the lungs, resulting in lower respiratory tract disease. That can develop into pneumonia.

In a clinical trial with nearly 25,000 participants, Arexvy was shown to be 83 percent effective in preventing lower respiratory tract disease caused by RSV in older adults. It was 94 percent effective against severe disease. The results were published this year in the New England Journal of Medicine.

Whom is this vaccine for?

Although people of all ages can become infected with RSV, this vaccine is approved for people 60 and older, who are at risk for severe illness because of their declining immune responses.

“Older adults, in particular those with underlying health conditions, such as heart or lung disease or weakened immune systems, are at high risk for severe disease caused by RSV,” Peter Marks, director of the Food and Drug Administration’s Center for Biologics Evaluation and Research, said in a statement.

GSK is conducting a clinical trial to test the vaccine in people as young as 50.

Does the vaccine have side effects?

As with many vaccines, common side effects included pain at the injection site, fatigue, muscle pain, headache and joint stiffness.

There were 10 cases of atrial fibrillation, a heart condition, within a month of vaccination in participants who received the shot, compared with just four cases in the placebo group.

There was also one case of Guillain-Barré syndrome, a rare neurological disorder in which the body’s immune system attacks nerve cells. In two patients who received the vaccine alongside the influenza vaccine, there were cases of acute disseminated encephalomyelitis, inflammation that affects the brain and spinal cord. One of those patients died.

The FDA is requiring the company to study the potential risk of Guillain-Barré and the brain and spinal cord inflammation as the vaccine goes into wider use. GSK will also track cases of atrial fibrillation.

Are more RSV vaccines coming?

Yes. Some experts call this the beginning of a renaissance for RSV. After decades of failure, new insights into the shape of a key RSV protein allowed scientists to create successful vaccines and a better preventive treatment.

A Pfizer RSV vaccine for older adults is under review, with a decision expected this month. The FDA is also reviewing the safety and effectiveness of Pfizer’s vaccine as a maternal vaccination, given during pregnancy. Virus-blocking antibodies are passed from mother to baby, providing the developing infant with temporary protection.

Moderna reported in January that its RSV vaccine was successful in protecting older adults and has said it plans to submit its data to regulators by the end of June. Another company, Bavarian Nordic, expects results from its RSV vaccine trial in the middle of this year, with plans to request approval from regulators if it is successful.

A monoclonal antibody developed by AstraZeneca and Sanofi also is under review; it can be used to provide vaccine-like protection to babies over an entire season. At this time, a monoclonal antibody made by Sobi is available to high-risk children and must be given once a month.

When will I be able to get this vaccine?

GSK plans to make the vaccine available in advance of the fall and winter RSV season.

In June, experts who advise the CDC on vaccines are anticipated to meet to make recommendations on how approved RSV vaccines should be integrated into public health care.