The Side Effects of RSV Vaccines

These post-shot symptoms “can happen with any vaccine,” says William Schaffner, M.D., a professor of medicine at Vanderbilt University School of Medicine in Nashville, Tennessee, and they’re generally a sign that the body is mounting an immune response.  

“There’s no free lunch out there. And there is no perfect drug or vaccine. All of them have some sort of side effects,” Schaffner says.

Scientists probe link between vaccines, Guillain-Barré syndrome

Serious side effects from vaccines are uncommon, but they can happen. A new report from the Centers for Disease Control and Prevention (CDC) finds that a small number of older adults developed a rare neurological disorder known as Guillain-Barré syndrome (GBS) after RSV vaccination.

Though its cause is not fully understood, GBS often occurs after an infection with a virus or bacteria, and on very rare occasions can develop in the days or weeks after getting a vaccine, the CDC says. When GBS occurs, the immune system mistakenly attacks part of the nervous system, resulting in symptoms that can range from mild (some muscle weakness) to severe (paralysis).

Most people who get GBS — 3,000 to 6,000 each year in the U.S. — fully recover from the syndrome, the CDC says, but some are left with permanent nerve damage. Although anyone can get it, adults 50 and older are at greatest risk.

Federal researchers analyzed data from VAERS and found about five cases of GBS were reported for every 1 million older adults who received Pfizer’s vaccine (Abrysvo), and about 1.5 cases of GBS were reported for every 1 million older adults who received GSK’s vaccine (Arexvy) from May 2023 to April 2024. The researchers acknowledge the rates were “more common than expected,” but they say the benefits of the shots outweigh the risks.

The risk for GBS is “very, very, very low,” Schaffner says. “And you have to compare it with the serious illness that RSV can produce in people older than 60 years of age.”

RSV typically causes cold-like symptoms, but in some cases, those symptoms can progress to a lung infection or pneumonia. RSV can worsen other health conditions such as asthma or chronic obstructive pulmonary disease (COPD). “Particularly as you get progressively older, the risk goes up for serious disease,” Schaffner says. “And that can be compounded if you have chronic underlying medical conditions.”

The CDC estimates that RSV sends 177,000 older Americans to the hospital annually; about 14,000 older adults die each year from an RSV infection.  

GBS was flagged as a rare side effect in the clinical trials testing the RSV vaccines. (The CDC report notes that findings from surveillance systems such as VAERS are “generally consistent with those from trials.”) A handful of cases of atrial fibrillation, or an irregular heart rhythm, were also reported in the clinical trials, and a small number have been picked up in the surveillance system. 

In the latest CDC report, the authors note that the CDC and FDA are “conducting active safety evaluations to assess risks for GBS and other adverse events of special interest after RSV vaccination.” The latest data does not change recommendations, “because the risk of RSV serious infection in these highly vulnerable populations is vastly greater than is the risk of Guillain-Barré,” Schaffner says.  

Questions? Talk to your doctor

If you’re concerned about potential side effects from the RSV vaccine, Talaat says you should talk to your doctor.

The RSV vaccine is recommended as a single dose for adults 75 and older and for people 60 to 74 who have health conditions that put them at higher risk for severe disease, such as lung or heart problems, or who live in a nursing home.

The CDC says the best time to get vaccinated for RSV is in late summer and early fall — “just before RSV usually starts to spread in the community.”