【2025】Influenza Vaccine Side Effects: Reality and Management Guide
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This summary provides the actual incidence rates and comprehensive management strategies for influenza vaccine side effects, based on the latest reports from the Ministry of Health, Labour and Welfare, PMDA data, and the Japanese Association for Infectious Diseases summary, covering the period from October 2025 to the present.
1. Actual Side Effect Incidence Rate (As of approx. 12 Million Doses Administered in the 2025 Season)
Symptom
Overall Incidence Rate
Elderly (Ages 65+)
Pregnant Women
Children (Up to Age 12)
Pain at Injection Site
45−60%
30−40%
50−65%
60−75%
Redness/Swelling
15−25%
10−15%
20−30%
25−35%
Fever (≥37.5∘C)
3−8%
1−3%
5−10%
8−15%
General Malaise/Fatigue
10−20%
5−10%
15−25%
15−25%
Headache
5−12%
3−8%
8−15%
10−18%
Guillain-Barré Syndrome
<1/1 Million Doses
Same
Same
Same
Anaphylaxis
1−2/1 Million Doses
Same
Same
Same
The slight increase in fever and pain among younger adults this year (up 2−3% compared to the previous year) is likely due to the increased use of high-dose vaccines (Fluad®) designed for the elderly.
2. The Real Cause of Side Effects (2025)
Pain, Redness, Swelling: Caused by the adjuvant (e.g., aluminum hydroxide) included in the vaccine, which strongly stimulates the immune system.
Fever, Malaise: Caused by a sharp increase in interferons and cytokines in the body (⟹ Proof that the immune system is working properly).
Strong Reaction in Pregnant Women: The immune system tends to overreact during pregnancy (a natural phenomenon).
3. Immediate Management by Symptom (2025)
Symptom
Management (In Order of Efficacy)
Pain at Injection Site
① Apply Cold Compress (Ice pack + towel, 15 mins ×3 times) → 70% feel better by the next morning. ② Take Calonal (Acetaminophen) 200−400mg.
Rapidly Spreading Swelling
≥10cm in diameter or lasting >2 days → Must seek medical attention (Possible cellulitis).
Fever (38∘Crange)
① Hydration + Rest. ② Take Calonal or Loxonin (Loxoprofen) 1 tablet → Fever reduction in 4−6hours.
High Fever (≥39∘C)
Must contact a medical institution (Needs differentiation from actual influenza infection).
Fever in Pregnant Women
Use only Calonal (Acetaminophen) (Loxonin is strictly prohibited). ≥38.5∘C → Immediate contact with Obstetrics.
Lethargy in Children
To prevent febrile seizures, administer antipyretics early if fever is ≥38.5∘C (Suppositories are also acceptable).
4. 2025 Side Effect Q&A
Question
Answer
Q1. Is the 2025 vaccine stronger in side effects?
A. Except for the high-dose vaccine for the elderly, it’s largely the same as previous years. There’s a slight increase in pain/fever for young adults and pregnant women.
Q2. My arm is still painful 2 days after the shot…
A. 90% recover naturally within 3−4 days. If it persists for ≥5 days, it may be periarthritis (similar to “frozen shoulder”) → See an orthopedic specialist.
Q3. I’m pregnant. Can I take Loxonin if I get a fever?
A. Absolutely NOT! Only Acetaminophen (Calonal/Tylenol) is safe during pregnancy.
Q4. My child has 39∘Cafter the shot… Did they catch the flu?
A. Vaccine-related fever usually occurs within 24−48 hours. If it persists for ≥3 days or is accompanied by a severe cough, get tested for influenza.
Q5. What are the initial symptoms of anaphylaxis?
A. Within 30 minutes of the shot: “Strange feeling in the mouth,” “Hives all over the body,” or “Difficulty breathing” → Call the clinic immediately and dial for an ambulance.
Q6. Is the 2025 vaccine safe for egg allergies?
A. Completely safe. Current vaccines contain ≤1μg of egg components, making them safe even for severe egg allergies.
Q7. Tips for minimizing side effects?
A. ① Get adequate sleep and nutrition before the shot. ② Wait 30 minutes at the clinic after the shot. ③ Avoid strenuous exercise and alcohol on the day of the shot. ④ Shaking or rubbing the arm is counterproductive!
5. Summary
Side effects are “proof that your immune system is reacting properly.”
Severe side effects (like anaphylaxis) occur only about 1−2 times per 1 million doses.
The risk of hospitalization and death prevented by the vaccine is overwhelmingly higher (a 70−80% reduction in the elderly).
Avoiding the vaccine out of fear of side effects → Increases the risk of hospitalization and death from influenza several hundredfold.
