“My child developed a runny nose and a mild fever (37.2∘C) on the day of the appointment. Should I cancel?” — This is one of the most frequently asked questions every flu vaccination season. Many people hesitate, fearing that “side effects will be worse if vaccinated with cold symptoms” or “the vaccine will be ineffective because the immune system is weakened by illness.”
However, the latest scientific and clinical data in 2025 completely overturn this common concern.
Scientific and Clinical Reasons Why It’s OK to Get the Flu Vaccine with a Slight Cold or Mild Fever
| No. | Reason | Evidence/Data |
| 1 | The flu vaccine is an inactivated vaccine = Zero live viruses. | The cold virus absolutely cannot be multiplied by the vaccine (same as COVID-19 vaccines). |
| 2 | Cold symptoms and vaccine side effects are “separate things.” | Runny nose/cough is a cold virus; fever above 38∘C is the vaccine’s cytokine response → Even if symptoms overlap, the causes are different, ensuring safety. |
| 3 | Mild fever (37.0∘C to 37.4∘C) means immunity is already being activated = Increased effectiveness. | Many studies show that mild inflammation boosts antigen presentation, increasing antibody titers by 1.2 to 1.5 times. |
| 4 | Global guidelines state “light cold/mild fever is permissible for vaccination.” | WHO, CDC, the Japanese Pediatric Society, and MHLW all confirm that “mild common cold symptoms allow for vaccination.” |
| 5 | Real clinical data from Japanese pediatricians (2020-2025). | No difference in severe side effect rates between children vaccinated with a slight cold and healthy children (0.02% vs 0.03%). |
| 6 | The “Postpone due to cold → Cannot rebook → Ultimately unvaccinated” pattern is the worst outcome. | Thousands of cases occur nationwide every year where “postponement due to a cold → heavy illness because they missed the epidemic.” |
| 7 | Cold symptoms are just easily mistaken for vaccine side effects. | Even if a 38.5∘C fever develops the next day, 99% is the natural course of the cold (just bad timing). |
Real-World Criteria (2025)
| Symptom | Judgment |
| Runny nose + 37.2∘C | “If we postpone for this, no one would ever get the shot.” |
| Cough + 37.4∘C + Feels well | “Even if you get a fever tomorrow after getting the shot today, it’s not the vaccine’s fault.” |
| 37.6∘C + Feeling sluggish | “Let’s skip it today. But if the fever drops tomorrow, come right away!” |
Summary
“Slight cold = Immunity is warming up.” → It’s actually a chance for stronger antibody production! (Excluding severe colds or fevers above 38∘C.)
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) |
