Influenza Vaccine Interval: 4 Weeks is Ideal for Children! Complete Summary & Best Schedule for Those Under 13

Children under the age of 13 require two doses of the influenza vaccine to build solid immunity. Receiving these two doses at the correct interval is the key to achieving maximum preventative effect.

The latest recommendation in Japan as of 2025 is for an interval of “2 to 4 weeks.” Specifically, what doctors honestly recommend as the timing that yields the “highest antibody level” is exactly 4 weeks later. Conversely, if the interval is shorter than the minimum of “at least 2 weeks (13 days),” the vaccination is not covered by insurance and the effectiveness is drastically reduced.

Influenza Vaccine “Interval” Guidelines

Example 2-Dose Schedule for Children (Under 13)

“Absolute Must-Follow Rules”

• The 2nd dose must be at least 13 days after the 1st dose → If shorter, it won’t be covered by insurance and the effect will drastically decrease.
• The maximum interval should not exceed 8 weeks (56 days) → If the gap is too long, the effect of the second dose will decline.
• Getting more than 2 doses in the same season is prohibited (Meaningless + not covered by insurance).

“Best Interval”

• “Exactly 4 weeks yields the highest antibody levels.”
• “3 weeks is a bit early, 5 weeks is a bit late.”
• “Exactly 2 weeks may reduce the effectiveness to about 70–80%.”

For children, the goal is to “get the 1st dose in October and finish the 2nd dose in November.” → This fully prepares them for the epidemic from December through March! Adults and teenagers (13+) only need 1 dose, so getting it done by the end of November is perfect!

Since today is November 22, 2025, if a child received their first dose around October 25th, they would be right on schedule for the ideal 4-week interval this week!

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: