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Despite pertussis epidemic, vaccination rates remained stable

VANCOUVER, British Columbia — Despite a pertussis outbreak in Washington state, no differences in vaccination rates were found among infants, according to data presented here.

From Oct. 1, 2011, to Dec. 31, 2012, Washington state experienced a pertussis epidemic, with infants being the hardest hit population.

Elizabeth R. Wolf, MD, FAAP, of the University of Washington, Seattle Children’s Research Institute, and colleagues compared infants up-to-date with diphtheria-tetanus-acellular pertussis vaccine (DTaP) before (n=39,500), during (n=40,811), and after (n=41,285) the epidemic. Inclusion criteria was met by children aged 3 to 8 months with at least one record in the Washington State Immunization Information System and documented county of residence.

“We chose infants because they are the age group that has the greatest risk of pertussis disease as well as complications,” Wolf said during a presentation. “They also receive the greatest number of vaccinations at one time.”

Up-to-date status was determined by one or more doses of vaccine at aged 3 months, two or more doses at aged 5 months, and three or more doses at aged 7 months.

Researchers sought to determine the effect of the epidemic on DTaP rates throughout the state and whether county incidence modified the effect.

No significant differences were found between up-to-status with DTaP among pre-epidemic and epidemic time points among the state level (absolute difference=2.1%; 95% CI, 1.6-5.9). No significant difference was found between pre-epidemic and post-epidemic vaccination rates.

“This is an unexpected result, one explanation may be that despite the epidemic, the fear of vaccine-related adverse events is greater than the fear of disease, which occurred during the 2009 swine flu epidemic,” Wolf said.

This was also true among infants in the study during both time points at the county level, despite incidence in county of residence.

“These results may challenge conventional wisdom that vaccine acceptance uniformly increases when risk of disease is high,” Wolf concluded. — by Amber Cox

For more information:

Wolf ER. Abstract #3380.7. Presented at: PAS 2014; May 2-6, 2014; Vancouver, British Columbia.

Disclosure: The researchers report no relevant financial disclosures.