Drugs › Respiratory syncytial virus Anti-F protein monoclonal antibody
Brand name · Nirsevimab
Beyfortus: adverse event reports filed with FDA
1,410 reports list it as a suspect or interacting product, 2023–2026. Class: Respiratory syncytial virus Anti-F protein monoclonal antibody.
- 1,410
- reports as suspect product
- 0% of all reports · about 513 a year
- 680
- reports, 12 months to June 2026
- 410 in the 12 months before
- 58.9%
- marked serious by the reporter
- 78.5% across the class
- 2.6%
- record death among outcomes, as reported
- 36 reports · not verified by FDA
1,410 adverse event reports received by FDA list the brand name Beyfortus (nirsevimab) as a suspect or interacting product, from October 2023 to June 2026. A further 4 reports list it only as a concomitant medication, and those are not counted in the figures on this page.
In the 12 months to June 2026, 680 reports listed it, up 66% from 410 in the 12 months before. FDA releases FAERS data quarterly, so the newest months are incomplete and grow in later releases. Over its reporting history that is about 513 reports a year and 0% of the 20,646,523 reports in the database, and 8.6% of the reports for the respiratory syncytial virus Anti-F protein monoclonal antibody class. How many people take it is not in the data, so a count is not a rate of occurrence.
Reporters most often recorded drug ineffective (18%), incorrect dose administered (15.1%) and respiratory syncytial virus bronchiolitis (14.3%). A report can list several reactions, so shares add to more than 100%; 212 different terms appear across these reports. Drug ineffective is recorded in 18% of these reports, a larger share than in the median respiratory syncytial virus Anti-F protein monoclonal antibody drug (1.5%).
58.9% of the reports are marked serious by the reporter (78.5% across the class); 2.6% record death among the outcomes and 38.2% record hospitalisation, as reported. 48% of the reports came from physicians, and the largest patient age group is under 2 (74%). FDA states that "a causal relationship cannot be established between product and reactions listed in a report" and that for any given report "there is no certainty that a suspected drug caused the event."
Reports by month, five years
Reports by the month FDA received them. FDA releases FAERS data quarterly, so the newest months are incomplete and grow in later releases.
By year received
2026 covers reports received through June 2026 only.
Reactions recorded in the reports
share of Beyfortus reports recording the termmedian drug in respiratory syncytial virus anti-f protein monoclonal antibody
- Drug ineffectivethe medicine did not work as expected18%254
- Incorrect dose administeredthe wrong dose was given15.1%213
- Respiratory syncytial virus bronchiolitis14.3%201
- Bronchiolitis9.4%133
- Pyrexiafever6.1%86
- Coughcough6%85
- Extra dose administered5.6%79
- Expired product administeredthe product was used past its expiry date3%42
- Respiratory syncytial virus test positive3%42
- Dyspnoeashortness of breath2.6%36
- Product storage errorthe product was stored wrongly2.6%36
- Oxygen therapy2.2%31
- Rashskin rash2.2%31
- Respiratory distressdifficulty breathing1.9%27
- Apnoeapauses in breathing1.8%26
- Rhinitis1.8%25
- Wheezingwheezing1.8%25
- Rhinorrhoeaa runny nose1.7%24
- Urticariahives1.6%23
- Poor feeding infant1.6%22
- Vaccination failure1.5%21
- Vomitingbeing sick1.4%20
- Infantile apnoea1.2%17
- Inappropriate schedule of product administrationthe product was taken at the wrong times1.1%15
- Pneumonialung infection1.1%15
- Respiratory syncytial virus bronchitis1.1%15
- Underdoseless than the intended dose1.1%15
Top 30 of 212 MedDRA preferred terms recorded across these reports, with a plain-language gloss where one is available. One report can record several terms. The hollow bar is the median share across the 3 drugs in the respiratory syncytial virus anti-f protein monoclonal antibody class; it describes the reports, not the patients. FDA states that adverse event reports "represent a small percentage of total usage numbers of a product", that "common products may have a higher number of adverse events due to the higher total number of people using the product", and that the data "by themselves are not an indicator of the safety profile of the drug or biologic."
Outcomes recorded
Outcome flags as the reporter set them; a report can carry several, and "other serious" is FDA's own category for serious reports outside the named outcomes. Grey bar: all 16,458 reports in the class. FDA has not verified any outcome and states that the reports "cannot be used to estimate the incidence of these events."
Patients and reporters
Patient age
Patient sex
Who reported
Age and sex as stated in the report; the reporter's qualification is the primary source recorded by FDA. 48.6% of reports give the United States as the country of the event or reporter.
Reason for use recorded
| Indication as recorded (MedDRA) | Reports | Share |
|---|---|---|
| Antiviral prophylaxis | 315 | 22.3% |
| Respiratory syncytial virus immunisation | 293 | 20.8% |
| Immunisation | 176 | 12.5% |
| Prophylaxis | 50 | 3.5% |
| Respiratory syncytial virus infection | 32 | 2.3% |
| Respiratory syncytial virus bronchiolitis | 3 | 0.2% |
The indication field is filled in by the reporter and is often blank; shares are of all 1,410 reports.
In context
| Measure | Beyfortus | Respiratory syncytial virus Anti-F protein monoclonal antibody | All reports |
|---|---|---|---|
| Reports as suspect product | 1,410 | 16,458 | 20,646,523 |
| Share of that pool | — | 8.6% | 0% |
| Reports, latest 12 months | 680 | — | 1,332,454 |
| Marked serious | 58.9% | 78.5% | 57.4% |
| Death recorded among outcomes, per 1,000 reports | 26 | 115 | 91 |
| Hospitalisation recorded, per 1,000 reports | 382 | 596 | 213 |
| Consumer-filed share | 11.3% | 32.7% | 45.8% |
| Top term, share of reports | Drug ineffective 18% | median 1.5% | 6.3% |
Shares are of reports, not of patients treated. The number of people taking a product is not in the data, so none of these figures is a rate, and differences between columns reflect who takes a product, who reports and how long it has been sold. FDA states that adverse event reports "represent a small percentage of total usage numbers of a product", that "common products may have a higher number of adverse events due to the higher total number of people using the product", and that the data "by themselves are not an indicator of the safety profile of the drug or biologic."
Other drugs in the respiratory syncytial virus anti-f protein monoclonal antibody class
| Drug | Name type | Reports | Latest 12 months | Marked serious |
|---|---|---|---|---|
| Synagis | brand | 14,497 | 82 | 79.7% |
| Palivizumab | generic | 551 | 112 | 99.1% |
Ordered by report count for navigation only. FDA states that adverse event reports "represent a small percentage of total usage numbers of a product", that "common products may have a higher number of adverse events due to the higher total number of people using the product", and that the data "by themselves are not an indicator of the safety profile of the drug or biologic." A brand and its generic are separate rows because reporters name them separately.
Questions about Beyfortus reports
How many adverse event reports has FDA received for Beyfortus?
1,410 reports list Beyfortus as a suspect or interacting product in the openFDA FAERS release of 28 Sep 2026, covering reports received through June 2026. 680 of them arrived in the latest 12 months. Another 4 list it only as a concomitant medication.
What reactions are recorded in Beyfortus reports?
drug ineffective (18%), incorrect dose administered (15.1%), respiratory syncytial virus bronchiolitis (14.3%), respiratory syncytial virus infection (12.6%) and bronchiolitis (9.4%). These are MedDRA preferred terms coded from what the reporter described; a report can list several, and a term's presence is not a finding that Beyfortus was responsible.
How serious are the reports?
58.9% are marked serious by the reporter. Among the outcomes recorded, 2.6% of reports include death and 38.2% include hospitalisation. FDA has not verified these outcomes and states that the reports "cannot be used to estimate the incidence" of the events.
Who files these reports?
physician (48%), other health professional (34.3%) and consumer or non-health professional (11.3%). Most reports reach FDA through the manufacturer, which must forward reports it receives.
Are reports for Beyfortus rising?
680 reports in the 12 months to June 2026, up 66% from 410 in the 12 months before. FDA releases FAERS data quarterly, so the newest months are incomplete and grow in later releases. Counts also move with how many people take a product, its time on the market and publicity.
Do these reports show that Beyfortus was responsible for these reactions?
No. FDA states that "a causal relationship cannot be established between product and reactions listed in a report" and that for any given report "there is no certainty that a suspected drug caused the event." The reaction may relate to the condition being treated, to other medicines, or to something else.
Is this a list of the side effects of Beyfortus?
No. It is a count of what was reported to FDA. The adverse reactions observed in clinical studies are printed on the FDA-approved label, which a pharmacist or clinician can go through with you.
How do I report an adverse event?
Consumers and health professionals can report to FDA through MedWatch (Form FDA 3500 online, or 1-800-FDA-1088), or to the manufacturer, which must pass reports on. See the guide on how to report.
Where this comes from. Counts are built from the openFDA Drug Adverse Event (FAERS) bulk export released 28 Sep 2026, which holds reports FDA received through 30 Jun 2026. Drug names are as reported, resolved to the brand or generic name on the FDA label where openFDA's harmonisation matched them; classes are the pharmacologic class (EPC) from the label and the National Drug Code Directory of 17 Sep 2026. A report counts here when it lists Beyfortus as a suspect or interacting product; reports listing it only as a concomitant medication (4) are excluded. No report narrative, lot number, patient detail or reporter identity is published. See the methodology and sources; FDA's record is authoritative, and corrections are handled within five working days.
Drug data (FAERS) through 30 Jun 2026; device data (MAUDE) through 31 Aug 2026. Not medical advice.