The time-associated impact of the Newborn Influenza Protection Act on infant influenza rates in New York State.
BACKGROUND
Influenza presents with increased morbidity and mortality in children ≤5 months of age. Vaccination of caregivers is indicated, but immunization rates are estimated at only 30%. The 2009 New York State Neonatal Influenza Protection Act (NIPA) mandated offering of influenza vaccine to caregivers during the post-partum hospitalization. The purpose of this study was to determine the impact of NIPA on infant influenza rates.


METHODS
Data on laboratory-confirmed influenza cases between 2006 and 2012 were extracted from the New York State Electronic Clinical Laboratory Reporting System (ECLRS). Data on infant cases were categorized by age (0-5 months) and location [New York City (NYC), outside NYC] based on reporting laboratory site. The total number of influenza cases and the percentage of total cases in the infant age group were normalized to the number of reporting laboratory sites. The χ2-test was used to compare the proportions of cases pre- and post-implementation. Year-to-year trends were assessed by linear regression. All tests of significance were two-sided and evaluated at the P<0.05 level.


RESULTS
During the 6-year study period, 3154 cases of infant influenza were detected. In bivariate analysis, 1707 (54.1%) of cases occurred prior to NIPA implementation and 1447 (45.9%) of cases occurred after (P<0.001). Of the 1422 total infant cases detected in NYC, the percentages of influenza cases pre- and post-NIPA were 54.6% (777) and 45.4% (645), respectively (P<0.006). Outside NYC, the percentage of infant cases was reduced from 53.7% (930/1732) to 46.3% (802/1732, P<0.02). Prior to implementation, there was a year-to-year increase in the number of infant influenza cases statewide (P<0.04 for trend). The ratio of infant influenza cases normalized per ECLRS site in NYC increased each year after NIPA passage (P<0.01 for trend). The ratio of infant cases outside NYC decreased annually (P<0.05 for trend). No year-to-year trends were seen in the percentage of total influenza cases in the infant age group compared to total cases across all age groups either within or outside NYC.


CONCLUSIONS
Comparison of three influenza seasons before and after NIPA suggests a total statewide reduction in infant influenza. However, the greatest driver of this reduction occurs from reduced disease in infants outside NYC. We speculate that, with increased crowding within NYC, parental immunization as encouraged by NIPA may not create cocoon immunity.
Shetal
S
Shah
Catherine
C
Messina
D017028:Caregivers / Q000331:legislation & jurisprudence*; D006760:Hospitalization; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D007252:Influenza Vaccines; D007251:Influenza, Human / Q000453:epidemiology / Q000517:prevention & control*; D016014:Linear Models; D009518:New York / Q000453:epidemiology; D010043:Outcome and Process Assessment, Health Care; D049590:Postpartum Period; D013997:Time Factors; D014611:Vaccination / Q000331:legislation & jurisprudence*
D007252:Influenza Vaccines