Protection against pertussis by acellular pertussis vaccines (Takeda, Japan): household contact studies in Kawasaki City, Japan

Effectiveness of an acellular pertussis vaccine in Japanese children during a non-epidemic period: a matched case-control study

The number of pertussis cases in Japan has decreased dramatically following the nationwide use of an acellular pertussis vaccine combined with diphtheria-tetanus toxoids (DTaP vaccines) which began in 1981. However, the effectiveness of the DTaP vaccine has not been systematically evaluated using appropriate epidemiological methods during a non-epidemic period in Japan. We evaluated the vaccine effectiveness (VE) of the Kaketsuken DTaP vaccine which contains two-component pertussis antigens in Japanese children from 1999 to 2001 using a matched case-control design and data from the Basic Resident Registration and Maternal and Child Health Handbooks. The DTaP vaccination history of 15 children with pertussis and 59 controls was obtained. The VE of 3 or 4 pertussis vaccinations compared with non-vaccination (baseline) was 96·9% for coughing attacks that lasted ⩾7 days, 96·4% for those lasting ⩾14 days, and 95·9% for those lasting ⩾21 days. These findings suggest that DTaP vaccination effectively prevented pertussis during a non-epidemic period in Japan.

Acellular pertussis vaccines

Although whole-cell pertussis vaccines have been highly effective in preventing whooping cough, their common and burdensome adverse reactions have spurred the development of safer alternatives. Seven acellular vaccines are licensed in one or more countries; four have been licensed thus far in the United States, and more may follow. Although the licensed acellular pertussis vaccines differ in their immunogenicity, adverse reactions, and efficacy, all are effective and, compared with whole-cell vaccine, are associated with markedly fewer and milder adverse reactions.

Factors influencing the spread of pertussis in households

The objective of this study was to compare the spread of pertussis in children and adults being secondary contacts after household exposure. The study was nested in an efficacy trial of an acellular pertussis vaccine. The spread of the disease was also monitored with respect to gender and antibiotic therapy. A total of 453 index cases, of which 133 were monitored for adult disease, fulfilled the WHO definition of pertussis. They had contacts to 173 unvaccinated children aged 6-47 months, and a total of 101 adults with pertussis were followed. Detection of the bacteria, or a significant increase of specific antibodies confirmed the diagnosis. Secondary spread of the disease was assumed, when a household member coughed for 7 days or more and had laboratory evidence for pertussis. Crude attack rates (AR) were 69% in children and 31% in adults (P < 0.05). AR in children were independent of gender but more women than men (P=0.02) were affected in those households where the index case was a child. Erythromycin treatment of the index case reduced the AR in exposed toddlers from 80% to 57% (P=0.06), and in exposed adults from 40% to 21% (P=0.2). Erythromycin therapy in contacts did not alter the clinical course of the disease significantly.

CONCLUSIONS

In a household study of pertussis, 69% of children and 31% of adults (more women than men) contracted the disease. Erythromycin reduced the number of infections in household contacts, but did not alter the clinical course in those who contracted pertussis.

Whole-cell and acellular pertussis vaccines

OBJECTIVE

To provide a review of pertussis vaccines, including information on efficacy, adverse reactions, and antibody production following administration of both whole-cell and acellular pertussis vaccines.

DATA SOURCES

A MEDLINE search and extensive review of journals was conducted to identify the information for this review.

DATA EXTRACTION

Pertinent studies reporting experience with pertussis vaccinations were reviewed.

DATA SYNTHESIS

The differences in efficacy, adverse reactions, and antibody responses between whole-cell and acellular pertussis vaccines are emphasized. The status of acellular pertussis vaccination in the US is defined.

CONCLUSIONS

Acellular (chemically detoxified or recombinant) pertussis vaccine formulation appears to cause fewer adverse reactions than whole-cell vaccine in most studies. Clinical efficacy and safety in the very young has not been well established. Thus, acellular pertussis vaccine is reserved for the 4th and 5th doses in the US. Oral or intranasal formulations of the pertussis vaccine are being evaluated.