Analysis of Outbreak of Varicella at a Day-Care Center Despite Vaccination Article by Galil Karin - Essay Example

Kona Vishnu Critical Analysis 19 November 2005 Critical Analysis of "Outbreak of Varicella at a Day-Care Center Despite Vaccination" Galil Karin and et al. The New England Journal of Medicine in an article named "Outbreak of Varicella at a Day-Care Center Despite Vaccination" stated that "Although the vaccine affords excellent protection against moderate and severe Varicella, a modified form of Varicella develops in some vaccinated persons after exposure to someone with an infectious case. By definition, these breakthrough cases occur more than 42 days after vaccination and are usually caused by wild-type virus." This implies that a modified form of Varicella may develop in a vaccinated person on exposure to an infected case and the effectiveness of vaccine is only for 42 days and also the infection may be due to a wild-type virus, thus defeating the very purpose of inoculation. 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 failure when it was dichotomized into vaccination at less than 14 months of age and vaccination at older ages. Firstly it implies that the vaccine is effective only for a period of three years. But the article contradicts this fact in the earlier paragraphs. Secondly it is not discussed any where regarding age at which the vaccine is to be administered and children below 12 months were not considered for statistical analysis at all. In the discussion part it is reported that "The cumulative attack rate among unvaccinated, susceptible children 12 months of age or older was approximately 86 percent in Building A and 9 percent in Building B. The low attack rate in Building B suggests that most children in this building were never exposed to Varicella." It is stated that the transmission of virus is through air and the two buildings in question are only 20 yards apart, then the results could be expected to be atleast consistent to some extent, but on the contrary the results are quiet different and not convincing. The article relies on reports given by parents or physicians for diagnosis, thus leading to either overestimating or underestimating the effectiveness of vaccine, further the article states that "the small number of children in the day-care center limited our ability to explore the independent effects of the time since vaccination and the age at vaccination in multivariate analyses." Hence the results cannot be totally relied on. The results ought to have been taken by laboratory testing and not through parents or physicians feedbacks. With all the contradictions it is reported that "Although the vaccine provided suboptimal protection against Varicella in this outbreak, it provided robust protection against moderate and severe Varicella and has reduced the incidence of Varicella dramatically in the United States. Given the approximately 11,000 hospitalizations and 100 deaths due to Varicella that occurred annually in the era before vaccination, vaccination remains the most effective strategy for protecting children and adults against illness and death due to Varicella." To conclude I feel that the effectiveness of vaccine formulation in question is doubtful and not 100%. Works Cited Galil Karin, M.D., M.P.H., Brent Lee, M.D., M.P.H., Tara Strine, M.P.H., Claire Carraher, R.N., Andrew L. Baughman, Ph.D., M.P.H., Melinda Eaton, D.V.M., Jose Montero, M.D., and Jane Seward, M.B., B.S., M.P.H. "Outbreak of Varicella at a Day-Care Center despite Vaccination." The New England Journal of Medicine Volume 347:1909-1915 December 12, 2002 Number 24. Read More