Latest Reported Side Effects (2025–2026)
Introduction
COVID-19 vaccines have been administered to billions of people worldwide since late 2020. They have substantially reduced severe disease, hospitalization, and death from SARS-CoV-2 infection. Like all medical products, COVID-19 vaccines can cause side effects — most of which are mild and transient — but rare and more serious reactions have also been identified through ongoing safety surveillance. Authorities including the U.S. Centers for Disease Control and Prevention (CDC), the World Health Organization (WHO), European Medicines Agency (EMA) and others continuously monitor vaccine safety and publish updated findings.
1. Common, Expected Side Effects
These are the effects most frequently reported in clinical trials and real-world use. They reflect the immune system’s normal response as the body builds protection.
Typical Common Side Effects
Most common vaccine reactions are mild to moderate, short-lived (1–3 days), and self-resolving:
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Pain, redness or swelling at the injection site
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Fatigue (tiredness)
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Headache
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Muscle aches (myalgia), joint pain
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Fever and chills
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Diarrhea
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Nausea
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Lymph node swelling (rare)
These symptoms are transient and indicate that the immune system is responding to the vaccine.
Example data from safety monitoring:
Between May 2024–April 2025, the Netherlands’ vaccine-safety database reported hundreds of cases of malaise, headache, fatigue, myalgia, chills and arthralgia (joint pain) among vaccine recipients — most of them mild and typical.
2. Severe Allergic Reactions (Rare)
Severe allergic reactions to COVID-19 vaccines are very rare, but they are a known safety concern and monitored globally.
Anaphylaxis
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An anaphylactic reaction can occur after vaccination, usually within minutes to an hour.
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Symptoms include difficulty breathing, rapid heartbeat, hives, swelling of the face or throat.
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Because of this risk, people are ordinarily observed for 15–30 minutes after vaccination at clinics, so treatment (e.g., epinephrine) can be given immediately if needed.
Risk level:
Rates of anaphylaxis are extremely low — on the order of about 1 case per 100,000 vaccinated persons in most monitoring systems.
3. Myocarditis & Pericarditis (Rare but Noted Signal)
Myocarditis (inflammation of the heart muscle) and pericarditis (inflammation of the outer lining of the heart) have been identified as rare adverse events following mRNA COVID-19 vaccines (e.g., Pfizer-BioNTech, Moderna).
Key Features
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Occur most often in young males, especially after the second dose of mRNA vaccines.
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Symptoms include chest pain, shortness of breath, and palpitations.
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Most cases are mild and respond well to rest and standard care, though some require hospitalization.
Mechanism & Timing
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Typically within 5–10 days post-vaccination for myocarditis.
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Pericarditis can appear somewhat later (1–3 weeks).
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Cases after booster doses are reported but rarer than after primary doses.
4. Guillain-Barré Syndrome (GBS) Signals Identified
The CDC’s Vaccine Safety Datalink surveillance system has reported a statistical signal for Guillain-Barré Syndrome (GBS) following mRNA COVID-19 vaccines in older adults (≥65). GBS is a rare neurological condition that causes weakness and sometimes paralysis.
What the Signal Means
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A statistical signal doesn’t confirm causation — it means more investigation is needed.
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If a real association exists, the additional cases are estimated to be similar to those seen after other adult vaccines (i.e., low frequency).
5. Stroke Signals (Under Study)
Surveillance also noted possible signals for ischemic stroke after certain vaccine formulations in older age groups — but evidence is not yet sufficient to confirm a safety issue. Studies are ongoing.
6. Very Rare or Inconclusive Signals
2.1. Reporting Systems vs Causation
Safety monitoring systems (e.g., VAERS, European EudraVigilance, Lareb in the Netherlands) collect reports of events following vaccination — but:
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A report of an event after vaccination doesn’t prove the vaccine caused it.
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Many reported events are coincidental (e.g., underlying conditions or unrelated health issues happening around the same time).
2.2. Chronic Fatigue & Long COVID-like Symptoms
Extensive review in Germany found no new safety signals for chronic fatigue or long COVID-like symptoms specifically following vaccination.
7. Pregnancy & Breastfeeding
Large data sets continue to indicate that COVID-19 vaccines do not increase risks of miscarriage, stillbirth, preterm birth, or birth defects. Vaccination offers protection against severe maternal COVID-19 infection, which itself is linked to adverse pregnancy outcomes.
8. Abnormal Uterine Bleeding Reports
Studies in South Korea and elsewhere have reported abnormal uterine bleeding (AUB) following COVID-19 vaccination — most reports being mild and self-limited, but under investigation to understand patterns and mechanisms.
Important note: such bleeding changes are not proof of causation and could be influenced by stress, infection, or hormonal fluctuations unrelated to the vaccine.
9. Side Effect Profiles by Vaccine Type
Different vaccines have somewhat different side effect patterns:
mRNA Vaccines (Pfizer-BioNTech, Moderna)
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Common: injection site pain, fatigue, headache.
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Rare: myocarditis/pericarditis, GBS signals in some age groups.
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Similar common reactions as mRNA vaccines.
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Very rare reports of myocarditis/pericarditis and allergic reactions are being monitored.
Viral-vector Vaccines
Some earlier vaccines (e.g., Adenovirus-based like Johnson & Johnson) have been phased out in many countries due to rare blood-clotting signals.
10. Data from Regulatory and Safety Agencies
FDA (U.S.)
Recent reporting indicates the FDA is considering adding a “black box warning” — the strongest label — to COVID-19 vaccines to highlight serious risks and restrictions, based on discussed safety signals like myocarditis.
EMA (European Medicines Agency)
EMA continues to list myocarditis/pericarditis, anaphylaxis, and Guillain-Barré among rare but monitored reactions, but emphasizes that overall benefits outweigh risks.
WHO & CDC Safety Reviews
Both WHO and CDC maintain that serious adverse events are rare and that the benefit–risk balance remains strongly positive. Vaccination continues to be recommended for eligible populations, including high-risk individuals and older adults.
11. Post-Marketing Surveillance Trends
Reporting Rates
National surveillance data show that:
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Reports of side effects continue to be collected and analyzed.
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Most reports are mild.
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Serious events are rare relative to the number of doses administered.
No New Safety Signals
Recent reports from national agencies (e.g., Paul-Ehrlich-Institut, Germany) indicate no new safety signals through the end of 2024 compared to prior years.
12. How Side Effects Are Monitored
COVID-19 vaccine safety is tracked through multiple, overlapping systems:
| System | Region | Description |
|---|---|---|
| VAERS | U.S. | Passive reporting of post-vaccine events |
| Vaccine Safety Datalink | U.S. | Active surveillance using health records |
| EudraVigilance | EU | European safety monitoring database |
| Lareb | Netherlands | National adverse event analysis |
| WHO global data | Global | Aggregated international safety signals |
These systems distinguish reporting from confirmed causality — scientists use statistical methods and clinical review to determine actual vaccine-related risks.
13. Interpreting Safety Data
Signal vs. Causation
A signal in vaccine safety surveillance means something unusual or unexpected was observed statistically — but it does not automatically prove the vaccine caused the event. Further study and clinical judgment are required.
Every health authority’s assessment weighs:
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The benefits of vaccination (prevention of severe COVID-19, hospitalization, death, long COVID).
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The risks of side effects.
For almost all groups, the benefits of COVID-19 vaccination are considered to outweigh risks, especially for older adults and people with underlying health conditions.
14. Special Populations
Children and Adolescents
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Reports of myocarditis are highest in adolescent males, but these cases are still rare and outcomes are generally good with treatment.
Pregnant & Breastfeeding People
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No evidence of increased risk of miscarriage or congenital anomalies directly due to vaccines.
Immunocompromised Individuals
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May have a reduced immune response, but vaccines are still recommended due to higher COVID-19 risks.
15. What Should You Do if You Experience Side Effects?
Mild reactions usually resolve within a few days — rest, hydration, and over-the-counter pain relievers may help.
Seek medical care immediately if you experience:
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Severe shortness of breath
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Chest pain or palpitations
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Fainting or severe headache
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Unusual bleeding or weakness
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Signs of anaphylaxis
16. Summary: Key Takeaways
| Type of Side Effect | Frequency | Notes |
|---|---|---|
| Injection site reactions | Very common | Mild, short-lived |
| Systemic symptoms (fever, fatigue) | Common | Normal immune response |
| Anaphylaxis | Rare | Treatable, short-term observation recommended |
| Myocarditis/Pericarditis | Very rare | Mostly mild, largest signal in young males |
| GBS signal | Rare signal | Under ongoing evaluation |
| Ischemic stroke signal | Under study | Not confirmed |
| Long-term chronic symptoms | No confirmed new signals | Anecdotal reports exist, but no causal link established |
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