Infectious Diseases-Related Hospitalizations During Oral Polio Vaccine (OPV) and Non-OPV Immunization Periods: An Empirical Evaluation of all Hospital Discharges in California (1985–2010)

Abstract

Abstract Background Live attenuated vaccines such as oral polio vaccine (OPV) can stimulate innate immunity and may have off-target protective effects on other pathogens. We aimed to address this hypothesis by examining changes in infectious diseases (ID)-related hospitalizations in all hospital discharges in California during OPV (1985–1996) and non-OPV immunization periods (2000–2010). Methods We searched the Office of Statewide Health Planning and Development database for all hospital discharges with any ID-related discharge diagnosis code during 1985–2010. We compared the proportion of ID-related hospitalizations (with at least 
1 ID-related discharge diagnosis) among total hospitalizations during OPV immunization (1985–1996) versus non-OPV immunization (2000–2010) periods. Results There were 19 281 039 ID-related hospitalizations (8 464 037 with an ID-related discharge diagnosis as the principal discharge diagnosis for the hospitalization) among 98 117 475 hospitalizations in 1985–2010; 9 520 810 ID hospitalizations/43 456 484 total hospitalizations in 2000–2010 versus 7 526 957/43 472 796 in 1985–1996. The risk ratio for ID-related hospitalizations in 2000–2010 versus 1985–1996 was 1.27 (95% confidence interval [CI], 1.26–1.27) for all diagnoses and 1.15 (95% CI: 1.15–1.16) for principal diagnoses. Increases also existed in the proportion of lower respiratory and gastrointestinal infections. Discussion The proportion of ID-related hospitalizations was lower in the OPV immunization period compared to the period after OPV was discontinued. When focused only on hospitalizations with ID as the principal discharge diagnosis, the signal remained significant but was smaller. These findings require replication in additional studies.