Pertussis booster important in second year of life

By Megan Brooks

NEW YORK (Reuters Health) - One or two doses of the diphtheria-tetanus-acellular pertussis (DTaP) vaccine provides good protection against pertussis in the first year of life, new research from Australia shows.

However, researchers also found the effectiveness of three doses wanes quickly in preschoolers without a booster dose.

Waning effectiveness of five doses of acellular pertussis vaccines is "well documented" after six years of age, but less is known regarding fewer doses in younger children, said Dr. Helen E. Quinn of the Australian National Centre for Immunisation Research and Surveillance of Vaccine Preventable Diseases in Westmead and colleagues in a paper online in Pediatrics February 10.

To investigate, they evaluated the effectiveness of one and two doses of the DTaP vaccine before six months of age and of three doses from six months to four years using a case-control approach.

They included 4584 Australian children, aged two to 47 months old, who had pertussis between 2005 and 2009. Each child with pertussis was matched to 20 children without pertussis.

The researchers found the vaccine's effectiveness in preventing pertussis hospitalization increased from 55.3% with one dose before four months of age to 83.0% for two doses received before six months of age.

The vaccine effectiveness of three doses was 83.5% between six and 11 months, 70.7% between two and three years of age, and 59.2% between three and four years of age.

This study shows that the "acellular pertussis vaccine provides protection from as early as the first dose, and good protection after two doses. This emphasizes the importance of having the first and second doses on time," Dr. Quinn told Reuters Health by email.

"This is an important study," Dr. Nicola P. Klein, who wasn't involved in the new research, noted in a telephone interview with Reuters Health. She is co-director of the Kaiser Permanente Vaccine Study Center in Oakland and senior research scientist in the Division of Research at Kaiser Permanente Northern California.

Until now, "there hasn't been a study that has actually looked at waning protection in younger children, especially after the infant doses, which is an important issue since infants are at such high risk for death and morbidity from pertussis," Dr. Klein explained.

Dr. Quinn and colleagues think their data have important implications for policy and practice in all countries using acellular vaccines.

"First, with respect to protection of young infants, our finding of robust protection after one or two doses argues for the first dose to be given as early as possible, with six weeks of age approved for the first dose by all major regulatory authorities. Second, they provide strong support for a booster dose in the second year of life, either as a delayed third dose after a two-dose primary schedule or a fourth dose if three primary doses are given before six months of age," the authors write.

Dr. Klein said "standard practice in the United States is to give a booster dose during the second year of life and so I think this tells us that we are doing the right thing by giving that booster dose."

The study was supported by the Communicable Diseases Network of Australia.

SOURCE: http://bit.ly/1gqAYk7

Pediatrics 2014.

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