How Long Do RSV Vaccine Side Effects Last?

For most people, RSV vaccine side effects clear up within one to three days. The most common reactions are injection-site pain, fatigue, and muscle aches, and they tend to peak within the first day or two before fading quickly. Severe reactions are rare, and fewer than two percent of vaccinated adults end up seeking medical care for any symptom linked to the shot. That said, the timeline can shift depending on which vaccine you received, whether you got it alongside another shot, and your overall health.

What the Most Common Side Effects Look Like

Three RSV vaccines are approved for older adults in the United States: GSK’s Arexvy (an adjuvanted protein vaccine), Pfizer’s Abrysvo (a bivalent prefusion F protein vaccine), and Moderna’s mResvia (an mRNA vaccine). Their side-effect profiles overlap heavily, though the rates differ. A systematic review covering all three products found that local injection-site pain occurred in roughly 23 to 29 percent of recipients and systemic symptoms appeared in about 7 to 11 percent.¹ Serious adverse events occurred in less than one percent of participants across clinical trials.

Those averages can mask meaningful differences between the two most widely used vaccines. A post-licensure study within a large Southern California health system surveyed more than 13,000 older adults who received either the GSK or Pfizer vaccine and tracked their symptoms for 14 days. The results showed a clear gap: about 57 percent of GSK recipients reported injection-site pain versus roughly 14 percent of Pfizer recipients. Fatigue was reported by about 36 percent of the GSK group compared to 22 percent of the Pfizer group, and muscle aches followed a similar pattern at about 26 percent versus 13 percent.² Fever was less common overall but still higher in the GSK group at about 8 percent compared to about 3 percent for Pfizer.

The higher reactogenicity with the GSK vaccine is not a surprise and is largely attributable to its AS01E adjuvant, a compound added to boost the immune response. Adjuvants are common in vaccines for older adults because the aging immune system responds less vigorously on its own. The trade-off is that adjuvanted vaccines tend to produce more noticeable short-term reactions. A phase 3 trial of the GSK vaccine found that about 60 percent of participants reported injection-site pain, about a third reported muscle aches, and a similar proportion reported fatigue.³ Only about 1.5 percent had a grade 3 (severe) local reaction, and about 3 percent had a grade 3 systemic reaction. So while you might feel more sore after the GSK shot than the Pfizer one, the overwhelming majority of those reactions are mild or moderate.

The One-to-Three-Day Window

The defining feature of RSV vaccine side effects is how fast they resolve. In a study of Italian older adults receiving the adjuvanted GSK vaccine, most solicited adverse events lasted one to three days, and only about 3.5 percent of participants experienced any reaction classified as severe.⁴ The phase 3 trial of the same vaccine reported a median duration of two days for both injection-site and systemic symptoms.³

In practical terms, if you get vaccinated on a Monday, you can expect any soreness or fatigue to peak by Tuesday and feel mostly normal by Wednesday or Thursday. Some people sail through with barely a sore arm, while others feel run down enough to want to take it easy for a day. The Southern California real-world study confirmed that these patterns hold outside of controlled clinical settings: most symptoms were transient and did not require medical care, with only about 2 percent of recipients in either vaccine group reporting that they sought care for a vaccine-related symptom.²

Getting the RSV Vaccine Alongside a Flu Shot

Many older adults wonder whether getting the RSV vaccine at the same visit as their annual flu shot will make the side effects worse or last longer. A clinical trial that gave adults 65 and older an RSV vaccine and high-dose influenza vaccine simultaneously found that the answer is mostly no. The frequency of local reactions in the RSV arm was about 71 percent whether the vaccines were given together or separately. The median duration of local side effects from the RSV component was two to three days when co-administered, compared to two to four days when given alone. Systemic reactions like fatigue and headache lasted a median of one to two days regardless of whether the flu shot was given at the same time.⁵

The flu shot arm itself produced slightly fewer local reactions (around 59 to 64 percent) with a median duration of one to two days, which is typical for influenza vaccines. Grade 3 local reactions were minimal in both arms, at about 0.5 to 1.2 percent. If you are planning to get both shots in one visit, the evidence suggests you will not be adding extra days of discomfort by doing so.

Do Booster Doses Feel Worse?

The question of RSV vaccine boosters is still evolving. Current recommendations for most older adults involve a single dose, but clinical trials have explored what happens with a second dose roughly 12 months later. In a phase 1 trial of Moderna’s mRNA-based RSV vaccine, the booster injection did produce more reactions than the first shot. However, the severity, the time it took for symptoms to appear, and the duration were all similar to the first dose.⁶ In other words, more people felt something after the booster, but it did not last longer or hit harder than the first time around.

This mirrors what we see with many other vaccines where a primed immune system responds more quickly and sometimes more vigorously to a second exposure. If and when RSV booster doses become routine, you can reasonably expect a similar one-to-three-day recovery window.

Side Effects in People With Weakened Immune Systems

People with compromised immune systems often worry about whether a vaccine will trigger an outsized reaction. With RSV vaccines, the evidence so far is reassuring. A study of immunocompromised individuals with blood cancers found that about 25 percent experienced mild reactogenicity, with no severe events reported.⁷ That is actually a lower rate than what healthy older adults typically report, which makes sense because a suppressed immune system tends to mount a weaker inflammatory response to a vaccine, producing fewer of the aches and fatigue that come from immune activation.

A large study of U.S. adults aged 60 and older found that the vaccine still provided substantial protection in immunocompromised individuals, with effectiveness against RSV-related illness ranging from about 67 to 73 percent depending on age group. Among transplant recipients, effectiveness was lower but still meaningful, though stem cell transplant patients saw the smallest benefit.⁸ The duration of common side effects in these populations has not been studied separately in enough detail to quote a different timeline, but nothing in the current data suggests they linger longer than in healthy adults.

Rare but Serious Adverse Events

The side effects most people experience are short-lived nuisances. But post-licensure surveillance has identified a rare but real signal for Guillain-Barré syndrome, a neurological condition that causes muscle weakness and sometimes temporary paralysis. GBS typically develops within a few weeks of vaccination rather than a few days, placing it in a completely different category from the transient soreness and fatigue that most people worry about.

A study of England’s older adult RSV vaccination program estimated the additional risk at about 23 cases per million doses, with the researchers concluding that this risk was far outweighed by the vaccine’s benefits.⁹ A U.S. analysis put the overall excess GBS risk at about 11 per million doses across both major vaccine brands, with the Pfizer product (Abrysvo) carrying a slightly higher estimated rate of about 18 per million and the GSK product (Arexvy) about 5 per million.⁸ Neither study found an excess risk of immune thrombocytopenia (a condition involving low platelet counts) after RSV vaccination.

Early clinical trial data had also raised questions about atrial fibrillation, a type of irregular heartbeat. Some trials showed slightly higher rates of atrial fibrillation in the vaccine group. A large population-based study settled this concern: RSV vaccination was not associated with an increased risk of new-onset or recurrent atrial fibrillation within 42 days, compared with people who received an influenza or Tdap vaccine instead.¹⁰ A separate large study confirmed that rates of heart failure hospitalization, heart attack, and atrial fibrillation did not differ between the RSV-vaccinated group and the unvaccinated group.¹¹

What VAERS Data Does and Does Not Tell You

If you search for RSV vaccine side effects online, you may come across alarming-sounding reports from the Vaccine Adverse Event Reporting System. VAERS is a passive surveillance tool run by the CDC and FDA. Anyone can submit a report, and the system captures events that happen after vaccination regardless of whether the vaccine caused them. A study analyzing more than 7,900 VAERS reports for the two major RSV vaccines identified dozens of statistical signals, including reports of immune thrombocytopenia and, for the Pfizer product used during pregnancy, signals related to pregnancy bleeding, fetal death, and reduced fetal movement.¹²

These signals are starting points for investigation, not proof that the vaccine caused any particular event. VAERS data cannot establish causation because it lacks a comparison group and relies on voluntary, unverified reports. However, the pregnancy-related signals are worth knowing about because they influenced the current recommendations around when Abrysvo is given during pregnancy, a topic covered below.

The Maternal Vaccine During Pregnancy

Pfizer’s Abrysvo is the only RSV vaccine approved for use in pregnant people, given between 32 and 36 weeks of pregnancy to protect the newborn through transferred antibodies. The side-effect experience for the mother is generally similar to what older adults report: arm soreness, fatigue, and headache that resolve within a few days.

The bigger concern during Abrysvo’s development was whether the vaccine might increase the risk of preterm birth or other complications for the baby. A systematic review and meta-analysis found that maternal RSV vaccination did not increase the risk of serious adverse events or preterm delivery.¹³ The vaccine’s approval window was limited to 32 to 36 weeks specifically because of a numerical imbalance in preterm births observed during the original trial when it was given earlier in pregnancy. Whether that imbalance was a true signal or a statistical fluke remains debated, but the narrowed window was adopted as a precaution.

Antibodies transferred from the vaccinated mother to the baby have a limited lifespan. RSV-specific antibodies in infants from vaccinated mothers have an estimated half-life of roughly 38 to 49 days, depending on the antibody type.¹⁴ This means the protection is strongest in the first couple of months of life and gradually fades, which is why the vaccine is timed to cover the infant’s first RSV season.

Nirsevimab for Infants Is a Different Story

Nirsevimab (brand name Beyfortus) is sometimes discussed alongside RSV vaccines, but it is actually a monoclonal antibody rather than a vaccine. Instead of training the immune system to make its own antibodies, it delivers pre-made antibodies directly. The distinction matters for side effects: because nirsevimab does not activate the immune system the way a vaccine does, the typical inflammatory reactions like muscle aches and fever are largely absent.

In a trial of healthy late-preterm and term infants, serious adverse events were reported in about 6.8 percent of infants who received nirsevimab and about 7.3 percent of those who received a placebo, meaning the rates were essentially identical.¹⁵ A meta-analysis of nirsevimab trials found no statistically significant difference between the treatment and placebo groups for serious adverse events, gastrointestinal events, or reactions graded as severe.¹⁶ A pooled analysis across all pivotal trials confirmed that most adverse events in nirsevimab recipients were mild or moderate and unrelated to the treatment itself.¹⁷

The most common reaction to nirsevimab in infants is mild irritation at the injection site. If your baby received nirsevimab and you are wondering how long side effects last, the honest answer is that most infants show no noticeable reaction at all. The long-term safety picture is still being filled in, as the meta-analysis authors noted, but the short-term data across thousands of infants is clean.

When to Call Your Doctor

For the typical injection-site pain, fatigue, headache, or low-grade fever, you can manage symptoms with over-the-counter pain relievers and rest. These should resolve within about three days. Contact your healthcare provider if you experience any of the following:

High fever: a temperature above 103°F (39.4°C) that persists beyond 48 hours
Weakness or tingling: progressive weakness in the legs or arms, especially if it starts in the feet and moves upward, which could signal Guillain-Barré syndrome
Severe allergic reaction: difficulty breathing, swelling of the face or throat, or a widespread rash, typically within minutes to hours of vaccination
Symptoms that worsen after day three: most vaccine reactions follow a clear trajectory of peaking early and fading, so new or worsening symptoms beyond the first few days deserve medical attention

GBS symptoms usually begin two to six weeks after vaccination, well outside the window when most people are monitoring for typical side effects. The condition is treatable, and most people recover, but early recognition matters. If you notice unusual weakness or numbness in your limbs in the weeks following vaccination, that warrants a call even if the common side effects resolved on schedule days earlier.