Important: VAERS reports alone cannot determine if a vaccine caused an adverse event. Reports may contain incomplete, inaccurate, or unverified information. Correlation does not equal causation.
Vaccine Side Effects
A comprehensive look at adverse events reported to VAERS (Vaccine Adverse Event Reporting System). This data shows what was reported after vaccination — not what was caused by vaccination.
What Are Vaccine Side Effects?
Vaccine side effects range from common, mild reactions like soreness at the injection site to rare, serious adverse events. VAERS collects reports of all health events that occur after vaccination, regardless of whether the vaccine caused them.
This distinction is critical: a VAERS report means something happened after vaccination, not because of vaccination. Someone who gets vaccinated and then catches a cold will generate a VAERS report, even though the vaccine didn't cause the cold.
Most Commonly Reported Side Effects
The most frequently reported symptoms in VAERS largely align with known, expected reactions to vaccination:
Vaccine-Specific Guides
In-depth side effect analysis for the most commonly searched vaccines:
Side Effects by Vaccine
Different vaccines have different side effect profiles. The table below shows the most-reported vaccines in VAERS. Click any vaccine to see its complete adverse event data.
| Vaccine | Reports | Deaths | Hospitalizations |
|---|---|---|---|
| Covid19 (covid19 (pfizer-biontech)) | 1,121,388 | 26,537 | 122,692 |
| Zoster Live (zostavax) | 140,312 | 397 | 4,720 |
| Influenza (seasonal) (fluvirin) | 119,695 | 1,081 | 8,325 |
| Varicella (varivax) | 93,126 | 308 | 3,357 |
| Measles + Mumps + Rubella (mmr Ii) | 89,976 | 497 | 5,174 |
| Hep B (engerix-b) | 73,280 | 1,522 | 5,447 |
| Pneumo (pneumovax) | 71,157 | 305 | 4,359 |
| Dtap (no Brand Name) | 66,714 | 1,457 | 5,590 |
| Hib (pedvaxhib) | 60,298 | 2,413 | 8,487 |
| Tdap (boostrix) | 52,846 | 129 | 2,191 |
Common vs Serious Side Effects
The vast majority of reported side effects are non-serious — things like headaches, fatigue, fever, and injection site pain. These are expected immune responses that typically resolve within days.
Serious outcomes (hospitalization, disability, death) represent a small fraction of all reports. Of 2,638,237 total reports:
- Hospitalizations: 232,938 (8.8% of reports)
- Deaths: 46,609 (1.8% of reports)
Remember: these are reported rates from a passive system, not actual risk rates. The real rate of serious adverse events from vaccines is much lower than what VAERS raw numbers suggest due to reporting bias and the denominator problem.
When Do Side Effects Occur?
Most vaccine side effects appear within the first few days after vaccination. Our onset timing analysis shows that the majority of reported adverse events begin within 0-3 days of vaccination, which is consistent with known immune response timelines.
You can explore onset patterns for any vaccine using our Onset Calculator tool.
Do Side Effects Go Away?
Our recovery rates analysis shows that the majority of people reporting adverse events to VAERS indicate recovery. However, VAERS lacks systematic follow-up, so "not recovered" often means the condition was still ongoing when the report was filed — not necessarily that it's permanent.
Understanding VAERS Limitations
Before drawing conclusions from this data, understand these key limitations:
- Anyone can file a report — VAERS is open to patients, parents, healthcare providers, and manufacturers
- Reports are not verified — the information may be incomplete, inaccurate, or coincidental
- Correlation ≠ causation — a report after vaccination doesn't mean the vaccine caused the event
- Underreporting exists — some events are never reported to VAERS
- Over-reporting also exists — media attention and legal incentives can increase reporting for specific vaccines
For a deeper understanding, read our articles on the denominator problem and reporting bias.