After getting the influenza vaccine, have you ever been told by a nurse or doctor, “Please take only a shower today and wait 6 hours before taking a bath”? Although many hospitals now say, “You can go right away,” this “6-hour post-vaccination waiting rule” stubbornly persisted as a long-standing custom in Japan.
Until When Was “No Bath for 6 Hours” Advised? The History and Reasons
| Period | Official/On-Site Advice | Who Said It? |
| ∼ 2000s | “Please refrain from bathing for 6 hours.” | Nearly 100% of hospitals and public health centers. |
| 2001 ∼ 2010 | “Preferably wait 6 hours…” | About half of the hospitals. |
| 2011 ∼ 2018 | “Shower is OK immediately, avoid long baths.” | Many pediatric clinics still advised 6 hours. |
| 2019 ∼ 2022 | “There are no specific bathing restrictions.” | MHLW and the Japan Pediatric Society officially withdrew the advice. |
| 2023 ∼ 2025 (Current) | Completely a thing of the past. | 99% of hospitals say, “It’s OK to take a bath immediately.” |
Why Did They Say “Wait 6 Hours” in the Past? (The True Reasons)
| Reason | Actual Truth |
| ① To prevent bacteria from entering the needle puncture site. | → Almost an urban legend. The flu vaccine is a subcutaneous/intramuscular injection, and the needle hole closes in a few minutes. There are zero reported cases of infection from bathing worldwide. |
| ② A lingering effect of the DPT (Diphtheria-Pertussis-Tetanus) vaccine. | → This is the true culprit! The old DPT vaccine contained a large amount of killed Bordetella pertussis bacteria, which often caused suppuration (pus formation) at the injection site. Bathing was genuinely observed to worsen these cases. |
| ③ Old vaccines had more impurities. | Older manufacturing methods from the 1970s ∼ 1980s carried a minor contamination risk (today’s vaccines are purified over 1,000 times more). |
| ④ Custom: “We’ve always said so.” | Unique Japanese culture of “Just in Case” (念のため文化, nen no tame bunka). |
The Official Withdrawal (The Decisive Moment)
- 2019: The Japan Pediatric Society explicitly stated on its website: → “Restrictions on bathing after influenza vaccination are not necessary.”
- 2021: The Ministry of Health, Labour and Welfare (MHLW) completely deleted the “wait 6 hours” notation from its vaccination guidelines.
- 2022 onwards: The advice was removed from new nursing textbooks.
The Current National Standard Rule (2025): “Only the 30-minute post-vaccination wait (for anaphylaxis countermeasure) is necessary; after that, baths and showers are immediately OK.” → It is standard practice for 99.9% of doctors, both pediatricians and internists, to say, “Please take a bath right away.”
Conclusion in One Word: The “wait 6 hours” rule is a lingering curse from the DPT vaccine 40 years ago. → As of 2025, it is a completely obsolete superstition!
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) |
