Targeting Pandemic Influenza Vaccine Reminders Using a Statewide Immunization Information System (IIS)

Background: Children with chronic conditions are at increased risk for influenza and related complications.  During the 2009-10 season, these children were considered priority cases for H1N1 and seasonal influenza vaccination.

Objectives: Describe the feasibility and utility of using a statewide IIS to target H1N1 and seasonal influenza vaccine reminders to chronically ill children during the 2009-10 influenza pandemic.

Methods: The Michigan Care Improvement Registry (MCIR) was used to identify 202,133 children with ≥1 chronic condition.  We excluded from analysis 53,516 children (26%) including: age <6 months or >18 years; received ≥1 dose prior to reminder; deceased; or, unknown address.  Reminders were mailed (12/7/2009); for each child receiving a reminder, a comparison group without chronic conditions was matched on birth month/year and county.  We evaluated H1N1 and seasonal influenza vaccination following mailing (through 1/31/10).

Results: A total of 6,234 (4%) reminders were returned as undeliverable. Among the remaining children receiving reminders (n=142,383), influenza vaccination was more frequent among children with chronic conditions (H1N1 7%, seasonal 5%) compared to their counterparts without chronic conditions (H1N1 4%, seasonal 3%), or with undeliverable reminders (H1N1 4%, seasonal 3%).  Vaccination rates remained relatively low at the end of the season among the entire MCIR population, both for those with chronic conditions (H1N1 24%; seasonal 24%) as well as no chronic conditions (H1N1 16%; seasonal 15%).

Conclusions: The feasibility of targeting mid-season vaccination reminders to priority cases during an influenza pandemic may be influenced by IIS reporting delays.  The low overall vaccination rates observed in MCIR, versus national estimates, may reflect incomplete dose recording.  This suggests limited ability to target mid-season reminders to unvaccinated children and to measure the effectiveness of such reminders during influenza pandemics.  Future initiatives should consider strategies to improve the timeliness and completeness of influenza dose reporting during pandemic events.