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Immunization prevented varicella hospitalizations in Australia
Children who were hospitalized in Australia for varicella were more likely to be unimmunized, according to study results published online.
Helen S. Marshall, MBBS, MD, MPH, of the Vaccinology and Immunology Research Trials Unit, Women’s and Children’s Hospital, Adelaide, Australia, and colleagues used coded data on discharge diagnoses from major tertiary hospitals in four Australian states both before and after varicella vaccine introduction in 2006. The investigators employed active surveillance to capture clinical features and genotyped the varicella strains.
Helen S. Marshall
With 80% coverage achieved, hospitalizations decreased 68%, the researchers said, adding that 80% of the children who were hospitalized were not immunized, including three immunocompetent children who needed intensive care. Of the children who were hospitalized, complications were less severe than in the pre-vaccine era.
“Our study findings provide strong evidence of the effectiveness of varicella vaccine in preventing not only severe cases of varicella requiring hospitalisation from complications but also in reducing severe cases of zoster,” Marshall told Infectious Diseases in Children.
Complications occurred in 44% of children, the most common of which included secondary skin infections (n=25) and neurologic conditions (n=14). There were no deaths; but three immunocompetent unimmunized children had severe multiple complications requiring intensive care. All strains genotyped were “wild-type” varicella, with clade 1 (European origin) predominating, according to the researchers.
“The results of our study support the need for increased awareness about severe varicella in the community and vaccination providers,” Marshall and colleagues wrote. “Previous studies have shown a lack of parental knowledge about varicella vaccination, but considerable concern about children acquiring the infection. Immunization of children who were ineligible by age or missed out on the funded program should be encouraged.”
Disclosure: Marshall reports no relevant financial disclosures.
Helen S. Marshall, MBBS, MD, MPH, can be reached at Department of Paediatrics, Women’s and Children’s Hospital, 72 King William Rd., North Adelaide, 5006, South Australia; email: helen.marshall@adelaide.edu.au.
Perspective
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The phrase, “Eternal vigilance is the price of liberty,” is attributed to an early American patriot, possibly Patrick Henry or Thomas Jefferson. This political rule might also be applied to vaccine programs. To be sure that routinely used vaccinations continue to be effective and provide freedom from disease, epidemiologic studies examining targeted illnesses in vaccine eras will always continue to be necessary.
Regarding the efficacy of varicella vaccine, Marshall and her Australian colleagues performed an important analysis of hospitalizations for severe varicella in Australian children. They conducted the study between 1999-2001, before introduction of varicella vaccine in that country, and between 2007-2010, after varicella vaccination was introduced, to analyze the effect of varicella vaccination in disease prevention. There was a 70% decrease in hospitalizations for varicella in vaccinees compared to non-vaccinees. Clearly the vaccine prevented severe varicella. Most hospitalized children (80%) had not been vaccinated and no vaccinated child with breakthrough varicella required intensive care in the hospital. It is interesting, however, that on occasion even a vaccinated child with breakthrough varicella had to be hospitalized.
Most of the infecting viruses were genotyped, which yielded significant virologic information. There were two recombinant viruses, although details of genotyping of these viruses nor the illness they caused were not described. There were also three Clade 2 (Asian) wild types although these too were not described as to whether they had some characteristics of the vaccine type (Oka) virus.
In particular, knowing whether these viruses had Pst1 restriction sites or not would be of great interest with regard to genotyping in the United States, where such viruses have only very rarely been described. In fact, they are unusual even in Japan, and very rarely described outside of Japan. Further analysis of these two types of viruses could provide significant epidemiologic information about the behavior of variacella-zoster virus (VZV). Clinical information on the illnesses theseVZVs caused would also be useful; for example whether they caused numerous skin lesions or pneumonia or were associated with bacterial superinfection or central nervous system complications.
The vaccinated children had received only one dose. These data also underscore the need for two doses to provide the best protection against varicella. The authors also fail to mention the main reason that two doses are necessary for high level protection, failure to seroconvert against VZV after one dose alone. Various studies have shown the rate of seroconversions to range from 95% to 76% after one dose. Primary vaccine failure after one dose is more likely to be the cause of breakthrough varicella than loss of immunity after one dose. Clearly two doses, as instituted for all children, provides better protection against VZV than one dose.
Continued disease surveillance over future years such as that performed in the current study will be needed to provide “eternal vigilance” resulting in freedom from VZV infections.
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