7,10 In our study serum IgA level was elevated

in 6-12% of infants <2years of age and in 4% of 6-year-old children. It has been reported that IgA against the PT antigen rises in 20-40% and IgA against the anti-filamentous hemaglutinin is increased in 30-50% of natural infections.7,10 In this study we measured IgA against three of Bordetella Inhibitors,research,lifescience,medical pertussis antigens (anti-pertussis toxin, anti-filamentous hemaglutinin and anti-lipopolysaccharides antibodies). Therefore, we presumed that the sensitivity of IgA in our study would be higher than the quoted figures for the measurement of separate antigens. Besides, as the half-life of IgA antibodies is considerably shorter than IgG, the presence of this antibody denotes a recent infection. Based solely on IgA levels, we estimated the prevalence of natural infection in our studied population of vaccinated children at ages of 4, 6, 12, 18, and 72 months to Inhibitors,research,lifescience,medical be between 9-11%, with the highest percentage was at 18 months. In infants aged 2 months, yet to receive their DwPT vaccination, 5% revealed evidence of recent exposure to Bordetella pertussis. Because of the low sensitivity of IgA, these records are believed to be only a part of the real figures. Some investigators

have used cut-off points for Inhibitors,research,lifescience,medical single serum samples derived from the mean+2SDs of anti-pertussis IgG to document natural infection.13-17 In our study we used a similar Inhibitors,research,lifescience,medical strategy to estimate the frequency of the naturally

infected vaccinated children through measuring anti-pertussis IgG. IgA positive children were excluded from each age group as naturally infected children. Then, a cut-off point of mean+2SD of the anti-pertussis IgG was assumed in the remaining samples (uninfected group) as the maximum level of vaccine induced antibody. Any rise from this level was considered as a natural pertussis infection. However, even these figures are an underestimation of naturally infected individuals, because inclusion of IgA negative but IgG positive individuals in the uninfected group would increase Inhibitors,research,lifescience,medical the mean IgG levels. Consequently, the cut-off point of mean+2SD would rise, resulting in the underestimation of truly infected children. Neither natural infection nearly nor vaccination against pertussis provides permanent immunity.3,4,9 The protective effect of the DwPT vaccine is reported to last for a varying Selleckchem ATM Kinase Inhibitor period from 4-12 years. Moreover, only about 52% of children would have a protective level of antibodies 4 years after receiving the vaccine.3,18 In a recent study from Australia it was noticed that the peak rate of pertussis had shifted from the age of 8-9 years to 12-13 years, after the 5th dose of the DwPT vaccine was introduced as a pre-school booster in 4-5 year-old children. The authors concluded that the protection provided by the DwPT vaccine declines 6-9 years after the last dose.