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Pertussis vaccination decreased severe illness, illness duration

Children immunized with acellular pertussis vaccine had less severe illness and significantly reduced illness duration, according to recent study findings.

Amy D. Sullivan, PhD, MPH, of the communicable disease services at Multnomah County Health Department in Portland, Ore., and colleagues evaluated 753 case reports of pertussis from Aug. 1, 2010, to July 31, 2012, to determine the effect of acellular pertussis vaccines (DTaP and Tdap). Of the patients, 633 were aged 6 weeks to 18 years and 98.7% had vaccination history and illness data.

Therapy was initiated in less than 20 days after cough onset in 75% of cases. Nineteen patients were positive for pneumonia with hospitalization in 12 patients. No deaths occurred.

Twenty-seven percent of patients were not up-to-date with their vaccines compared with 46% who were up-to-date. Ninety-three percent of the 453 patients who were ever vaccinated had received acellular pertussis vaccines only, according to the results published in Clinical Infectious Diseases.

Decreased odds of hospitalization and frequency of pneumonia were seen among all vaccinated patients whether up-to-date or not up-to-date compared with those who were never vaccinated. Hospitalizations were five times less likely among vaccinated patients, they were also 2.5 times less likely to develop severe illness compared with patients who were never vaccinated.

During the study period, 67% of patients stopped coughing.

“While pertussis vaccination alone may not completely prevent illness, even incomplete vaccination decreases cough duration and protects against severe disease manifestations,” the researchers wrote. “Our results suggest that the current Advisory Committee on Immunization Practices (ACIP) immunization guidelines are effective at limiting individual-level pertussis severity and morbidity,” the researchers wrote. “However, reducing the high proportion of breakthrough infections at the population-level may necessitate improved vaccine formulations and wider coverage. Also, as the protective effect of vaccination was found to be independent of antimicrobial therapy, both vaccination and early treatment strategies are likely to be important for improving outcomes.”

The researchers also said they strongly recommend adherence to the ACIP vaccination guidelines and early initiation.

In an accompanying editorial, Jussi Mertsola, MD, of the department of pediatrics at Turku University Hospital and Turku University in Finland, wrote that the study results stress the importance of high vaccine coverage.

“The important question is, are we able to get with the current vaccines high enough herd immunity in the whole population to effectively protect the vulnerable young infants under the vaccination age,” he wrote. “The cumulating data indicates that the answer is negative.”

For more information:

Barlow RS. Clin Infect Dis. 2014;doi:10.1093/cid/ciu156.

Mertsola J. Clin Infect Dis. 2014;doi:10.1093/cid/cui161.

Disclosure: The study was funded in part by the CDC. The researchers report no relevant financial disclosures.