SAFETY AND IMMUNOGENICITY OF HYDROGEN PEROXIDE-INACTIVATED PERTUSSIS TOXOID IN 18-MONTH-OLD CHILDREN

The immunogenicity and adverse effects of an acellular pertussis vaccine consisting of a purified pertussis toxin inactivated with hydrogen peroxide (PTxd) was evaluated. Children aged 15 to 30 months were injected with 10 (n = 33) or 50-mu-g (n = 34) of PTxd or with diphtheria and tetanus toxoids and whole cell pertussis vaccine (DTP) (n = 34). All children had previously received three doses of DTP during infancy. Both dosages of PTxd induced higher IgG antibody (p < 0.05 for 10-mu-g dose and p < 0.01 for 50-mu-g dose) and pertussis antitoxin responses (p < 0.01 for 50-mu-g dose) than DTP. The 50-mu-g dose gave slightly higher (though not significantly) antibody responses than the 10-mu-g dose of PTxd. None of the vaccines induced detectable IgM or IgA antibody responses to pertussis toxin. At 24 h, local reactions occurred in none of the children injected with 10-mu-g PTxd, 12% with 50-mu-g PTxd and 78% with DTP. Fever at 24 h occurred in 13% after 10-mu-g PTxd, in none after 50-mu-g PTxd and in 53% after DTP. Recipients of DTP, but not of PTxd, had significant increases in neutrophils and decreases in lymphocytes and haematocrit at 24 h (all p < 0.05). None of the groups showed changes in blood glucose at 24 h. PTxd induced pertussis toxin antibody levels similar to those observed in patients convalescing from natural pertussis. This acellular pertussis vaccine deserves further evaluation for safety and immunogenicity in infants and for efficacy in preventing pertussis.