RSV vaccines have a strong overall safety profile, with most side effects being mild and short-lived. In clinical trials involving tens of thousands of participants, serious adverse event rates were essentially the same in vaccinated and unvaccinated groups. That said, a few rare signals, particularly a small increased risk of a neurological condition called Guillain-Barré syndrome, have prompted ongoing monitoring. Here’s what the data actually shows.
Common Side Effects in Older Adults
RSV vaccines are currently recommended for adults 60 and older, and the side effect profile in this group looks similar to what you’d expect from a flu shot. In the large phase 3 trial for Moderna’s mResvia vaccine, the most frequently reported reactions were injection site pain (56%), fatigue (31%), headache (27%), muscle pain (26%), joint pain (22%), and chills (12%). The vast majority of these were mild or moderate. Only about 3% to 4% of reactions were rated severe.
Serious adverse events, the kind that require hospitalization or are medically significant, occurred at nearly identical rates in the vaccine and placebo groups: 7.8% versus 7.9% over roughly 10 months of follow-up. That’s an important number because it suggests the vaccine itself isn’t driving serious health problems beyond what would happen naturally in this age group.
The Guillain-Barré Signal
The most closely watched safety concern is Guillain-Barré syndrome (GBS), a rare condition where the immune system attacks the nerves, causing weakness and sometimes temporary paralysis. Early real-world monitoring through the CDC’s reporting system found GBS reports at rates of 1.8 to 4.4 cases per million doses administered, depending on the vaccine brand. Both figures are higher than the expected background rate in a population that age.
To put this in perspective, GBS occurs naturally in about 1 to 2 people per 100,000 each year regardless of vaccination. The signal here is small in absolute terms, but it’s real enough that the CDC and FDA continue to track it closely. This is one reason the vaccines are recommended with “shared clinical decision-making” rather than as a universal recommendation for all older adults. If you have a history of GBS, this is worth discussing before getting vaccinated.
Atrial Fibrillation: A Small Imbalance
In clinical trials for Pfizer’s Abrysvo vaccine, FDA reviewers noted a slight numerical imbalance in atrial fibrillation (an irregular heart rhythm) within the first month after vaccination: 10 cases in the vaccine group compared to 4 in the placebo group. Both numbers represent less than 0.1% of participants, so the absolute risk is very low. It hasn’t been established as a causal effect, but it’s on the radar for post-market surveillance.
Safety During Pregnancy
Abrysvo is the only RSV vaccine approved for use during pregnancy, given between 32 and 36 weeks of gestation to protect newborns. The key safety question here has been preterm birth. When the vaccine was tested across a broader window of 24 to 36 weeks, researchers observed a slightly higher rate of preterm delivery compared to the narrower 32-to-36-week window. The FDA concluded there isn’t enough data to confirm or rule out a causal link, which is why the approved timing is restricted to that later window.
For newborns, rates of neonatal jaundice were similar between vaccine and placebo groups (7.2% versus 6.7%), and other infant health outcomes like eczema, asthma, and reflux showed no meaningful differences. The FDA approved the vaccine after determining that adverse event rates in both mothers and infants were not significantly different from placebo.
Getting RSV and Flu Shots Together
Many people in the target age group want to get their RSV vaccine at the same visit as a flu or COVID-19 shot. A phase 3 trial tested this directly with the Moderna RSV vaccine given alongside a standard flu vaccine. Local reactions (soreness at the injection site) were similar whether the vaccines were given together or separately. Systemic reactions like fatigue and muscle pain were slightly more common with co-administration, but the difference was small and driven mainly by mild increases in tiredness and soreness. Getting both vaccines at once does not appear to create a meaningfully worse experience for most people.
People With Weakened Immune Systems
RSV vaccines are not live vaccines, so they don’t pose the theoretical risk of causing infection in immunocompromised people. However, the clinical trials that led to approval mostly enrolled healthy older adults, leaving significant gaps in data for people with conditions like organ transplants, active cancer treatment, or autoimmune diseases on immunosuppressive therapy. The Infectious Diseases Society of America’s 2025 guidelines note that vaccine effectiveness is likely lower in immunocompromised individuals, and tailored approaches are still being studied. The vaccines are not contraindicated in this group, and current guidance supports giving RSV, flu, and COVID-19 vaccines together for immunocompromised patients.
Who Should Not Get the Vaccine
The only firm contraindication is a history of severe allergic reaction (anaphylaxis) to any component of the specific vaccine product. Each vaccine has its own formulation, so if you’ve had a reaction to one brand, it doesn’t necessarily rule out the other. The ingredient lists are available in the package inserts, and your pharmacist or doctor can review them with you if you have known allergies to vaccine components.
How Safety Is Being Tracked
Because RSV vaccines are relatively new, post-market monitoring is ongoing through multiple systems. The CDC uses VAERS (Vaccine Adverse Event Reporting System) to collect reports of any adverse events after vaccination, and V-safe, a smartphone-based tool where vaccinated individuals can log how they feel in the days and weeks afterward. Anyone, not just healthcare providers, can submit a VAERS report. The CDC has committed to monitoring real-world safety and effectiveness each respiratory virus season, which means the safety picture will continue to sharpen over time.