25538 Influenza A (H1N1) Epidemic Course within and Between States and H1N1 Influenza Vaccine Uptake, 2009-2010

Tuesday, March 29, 2011
Columbia Hall
Carla Black, PhD , Epidemiologist, Centers for Disease Control and Prevention

Background:   The course of the 2009 H1N1 epidemic varied by state, and in many states the peak in disease activity had passed before the vaccine became available in mid-October.

Objectives:  Examine the association between the course of the 2009 H1N1 epidemic and attitudes regarding risk of acquiring H1N1 and H1N1 vaccination coverage.

Methods:  The peak of the epidemic in each state was approximated by the peak week of influenza emergency department visits between April 2009 and March 2010 as determined using electronic healthcare reimbursement claims submitted to SDI Health, a medical claims warehouse. H1N1 vaccination coverage estimates and attitudes regarding risk of acquiring H1N1 during October and November 2009 were obtained from the National 2009 H1N1 Flu Survey, a national random-digit dial telephone survey.

Results:  Final season H1N1 vaccination coverage levels were significantly lower for states with an early epidemic peak before October 10, 2009 (19.8%; 95% CI:16.4-23.7) than for states with an epidemic peak October 31, 2009 or later (30.4%; CI:27.5-33.6) (p=0.0001). Among residents of states with an early epidemic peak, concern about becoming ill with H1N1 peaked at 43.2% during the week ending October 24, and steadily decreased to a low of 23.4% during the week ending November 7. Conversely, among states with a late disease peak, concern about acquiring H1N1 steadily increased throughout the survey period to a high of 41.2% during the week ending November 14.

Conclusions:  The association between a late epidemic peak and higher vaccination coverage suggests that higher epidemic activity near the time when H1N1 vaccine became available had an impact on vaccine-seeking behavior. The level of concern about acquiring disease was highest in those states where disease activity peaked when H1N1 vaccine became available. Earlier availability of vaccine in areas with early disease activity may facilitate higher vaccination coverage in future pandemics.