Does a 15-Year-Old Need Two Doses of Flu Vaccine?
No, a 15-year-old needs only one dose of influenza vaccine per season, regardless of prior vaccination history. 1
Age-Based Dosing Algorithm
The number of influenza vaccine doses required is determined by age at the time of first dose administration:
Children 9 Years and Older (Including 15-Year-Olds)
- Require only 1 dose per season 1
- This applies regardless of:
Children 6 Months Through 8 Years
- Require 2 doses (at least 4 weeks apart) if they have received fewer than 2 doses of any influenza vaccine before July 1 of the current season 1
- Require only 1 dose if they have previously received 2 or more total doses of any influenza vaccine before July 1 of the current season 1
Rationale for Single-Dose Recommendation
The two-dose requirement for younger children is based on immunogenicity studies showing that vaccine-naive children need both a priming dose and booster dose to mount adequate antibody response 2. However, by age 9 years, children have typically had sufficient prior exposure to circulating influenza strains (either through natural infection or vaccination) to respond adequately to a single annual dose 1.
Studies demonstrate limited or no improvement in antibody response when a second dose is administered to adults and older children during the same season 1. The pooled absolute increase in vaccine effectiveness of a second dose was only 15 percentage points for children younger than 9 years, and this benefit was not statistically significant when the age range was broadened 3.
Common Pitfalls to Avoid
- Do not delay vaccination to obtain a specific vaccine product—any available age-appropriate influenza vaccine should be administered 1
- Do not confuse first-time vaccination status with age-based requirements—for children 9 years and older, even first-time recipients need only 1 dose 1
- Do not administer a second dose to a 15-year-old who received one dose earlier in the same season, as this provides no additional benefit 1