Further the article states "To date, there is no evidence of an increase over time in the rate of breakthrough disease that would suggest waning immunity after vaccination." Then why does a person get infected after 42 days (though mildly)
In the case definition it is stated "We defined a case of natural Varicella as an illness involving a pruritic, maculopapulovesicular rash with no other apparent cause beginning from December 1, 2000, through January 11, 2001, in a child attending the day-care center who had not received Varicella vaccine or who had been vaccinated less than 14 days before the onset of rash. Breakthrough disease was defined as Varicella in a child who had been vaccinated more than 42 days before the onset of rash." Varicella here is defined in two ways first is natural Varicella and the second is Breakthrough disease, but what is the exact definition Is it that the second version is advanced form of Varicella infection or failure of the vaccine
In the statistical analysis "The effectiveness of the vaccine against moderate-to-severe disease was calculated by classifying mild cases as noncases." First and foremost it is not understood as to why children less then 12 months age and children with history of Varicella disease are not considered (numbering 18 children) And how could the mild cases be considered as noncases and ignored Everywhere in the paper stress is laid on the boys, why What about girls Is the Varicella disease restricted to only boys
In the Investigations on Index Case section it is stated "His only known exposure to Varicella-zoster virus was contact with an 11-year-old sister who did not attend the day-care center and who had herpes zoster (confirmed by Tzanck testing)." Point to be noted here is that the index patient was in contact with his sister, who was already infected by herpes zoster and not by Varicella zoster as stated in the article. Did this contact have any effect on already Varicella inoculated index patient The index patient though vaccinated earlier has become a carrier in this case.
In the outbreak section it is stated that the effect on 17 vaccinated cases were mild and in 8 unvaccinated cases was moderate or severe out of a total 25 cases and no infants or children with a history of Varicella disease were reported. The section further states that "No child had a severe complication of Varicella or required hospitalization. As compared with unvaccinated children, those who had been vaccinated had milder disease, had new lesions on fewer days, had rash that crusted more quickly, missed fewer days of day care, and were less likely to have fever." Here the table indicates that vaccinated cases were marginally better over unvaccinated cases.
In the risk for vaccine failure section it is stated
Two continuous variables - time since vaccination and age at vaccination - were associated with the risk of vaccine failure. Children vaccinated three or more years before the start of the outbreak had more than twice the risk of disease found among those vaccinated within three years before the outbreak. Age at vaccination did not remain significantly associated with vaccine