Factors increasing risk for pertussis in children evaluated

By Helen Albert, Senior medwireNews Reporter

Research shows that children with pertussis infection are significantly less likely to have had all five diphtheria, tetanus, and acellular pertussis vaccine (DTaP) doses than uninfected children.

Risk for pertussis infection also increased significantly with increasing number of years since vaccination, notes the team, "consistent with a progressive decrease in estimated vaccine effectiveness each year after the final dose of pertussis vaccine."

Lara Misegades (US Centers for Disease Control and Prevention, Atlanta, Georgia, USA) and colleagues analyzed data collected from 682 suspected, probable, and confirmed pertussis patients aged 4-10 years, who were diagnosed between January and December 2010 during the California outbreak.

For each child with pertussis, three matched controls without pertussis who were treated by the same clinicians as the patients were selected (n=2016).

As might be expected, significantly more patients than controls had received no pertussis-containing vaccines, at 7.8% versus 0.9%.

Writing in the Journal of the American Medical Association, Misegades and co-workers report that children with pertussis were a significant 89% less likely to have received all five doses of the DTaP vaccine than controls.

When time since completion of the DTaP series of vaccinations was taken into account, children who had pertussis were significantly less likely to have had their fifth dose of vaccine in the last 12 months than controls, at 2.8% versus 17.6%.

This discrepancy increased with increasing time since last DTaP vaccination, showing a steady decline in vaccine efficacy with number of years since last vaccination.

"The increasing incidence of pertussis, changing epidemiology, and demonstrated decline in the estimated DTaP vaccine efficacy over time have raised concerns about the current U.S. pertussis vaccine program and may prompt consideration of alternative schedules," write the authors.

"Ultimately, improved control of pertussis may require a vaccine that provides longer duration of protection or differently affects transmission in the community," they conclude.

Writing in an accompanying editorial, Eugene Shapiro (Yale university School of Medicine, New Haven, Connecticut, USA) commented: "Although there have been substantial accomplishments in controlling pertussis with vaccination, the success has been far from complete. Recent data highlight the need to develop pertussis vaccines with acceptable adverse effects that induce more durable immunity and to use such vaccines to maintain immunity in the entire population."

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