One of the biggest reasons people hesitate to get the influenza vaccine may be anxiety over “severe side effects.” Serious adverse reactions like anaphylaxis, Guillain-Barré Syndrome (GBS), and Acute Disseminated Encephalomyelitis (ADEM)—which sound alarming—do indeed exist.
However, the latest data from the Ministry of Health, Labour and Welfare (MHLW) and clinical practice as of 2025 demonstrates that the frequency of these occurrences is extremely rare. Anaphylaxis occurs in only 1 to 2 people per million—a rate less than 1/10th the chance of dying in a plane crash and less than 1/1000th the chance of dying in a traffic accident.
Reality of Individuals with “Actual Severe Side Effects” from the Flu Vaccine (2025 Latest MHLW Reports + Clinical Summary)
| Type of Severe Side Effect | Frequency (Actual Data in Japan) | Who is Most Susceptible? | Example of Actual Symptoms |
| Anaphylaxis | Approx. 1–2 per 1 million people | Severe egg allergy, rubber (latex) allergy, history of anaphylaxis to vaccines | Difficulty breathing, drop in blood pressure, full-body hives 5–20 minutes post-shot |
| Guillain-Barré Syndrome (GBS) | Approx. 1 per 2–3 million people | Slightly more common in men aged 50–70s | Weakness in hands and feet starting 1–3 weeks post-shot |
| Acute Disseminated Encephalomyelitis (ADEM) | Approx. 1 per 5 million people or less | Extremely rare in children | High fever + impaired consciousness + seizures |
| Thrombocytopenic Purpura | Approx. 1 per 3 million people | Slightly more common in children | Bruising all over the body 1–3 weeks post-shot |
| Severe Local Reaction (Cellulitis-like reaction) | Approx. 1 per 10,000 people | Slightly more common with Fluad (for elderly) | The injected arm swells tightly, accompanied by a 39°C fever for 3 days |
“People Who Should Truly Be Careful” List (2025)
| Person | Must Consult a Doctor / Should Refrain |
| History of Anaphylaxis to the Influenza Vaccine | Absolute Contraindication (Cannot get the shot) |
| History of Anaphylaxis due to an Egg Allergy | Standard vaccine is NG → Recombinant Vaccine is OK |
| History of Guillain-Barré Syndrome | Must consult a doctor (Risk vs. Benefit assessment) |
| Fever of ≥37.5∘C on the day of vaccination | Postpone the appointment |
| Severe Immunodeficiency (High-dose steroids, undergoing chemotherapy) | OK for inactivated vaccines, but requires doctor’s judgment |
Conclusion
The probability of a severe side effect is:
- Less than 1/10th the chance of dying in a plane crash.
- Less than 1/1000th the chance of dying in a traffic accident.
- Only a few hundred to a thousandth of the chance of dying or being hospitalized from the flu itself.
Therefore, saying “I won’t get the shot because I’m afraid of severe side effects” is completely counterproductive.
For seniors and those with underlying conditions, “Not getting the shot is 100 times more dangerous!”
At-Home Testing Kit Ranking (Combined COVID-19 and Influenza)
Here is the English translation of the ranking table for at-home diagnostic kits that test for both COVID-19 and Influenza A/B:
| Rank | Product Name (Manufacturer) | Targets Detected | Sensitivity (Detection Rate) (Estimate: 12-48h Post-Onset) | Result Time | Approximate Price (Per Test) | Suitability for Pregnant Women / Children | Key Features & Availability |
| 1 | Panbio COVID-19/Flu A&B | COVID + Flu A/B | COVID: Approx. 90% | Flu: Approx. 85% | 15 mins | ¥1,980 – ¥2,480 | ◎ (Shallow Nasal Swab) |
| 2 | クイックナビ-Flu+COVID | Same (COVID + Flu A/B) | COVID: 88% | Flu: 80–85% | 15–20 mins | ¥1,780 – ¥2,200 | ◎ (Designed for children’s use) |
| 3 | KBMラインチェック nCoV/Flu | Same (COVID + Flu A/B) | COVID: 85% | Flu: Approx. 80% | 15 mins | ¥1,480 – ¥1,980 | ◎ |
| 4 | イージードック Flu＆COVID-19 | Same (COVID + Flu A/B) | COVID: 87% | Flu: 82% | 15 mins | ¥2,200 – ¥2,600 | ◎ (Many cases of use by pregnant women) |
