Response to a letter to the editor regarding ' the comparison of seroconversion rates among different varicella vaccines administered Turkish children; MAV/06 and vOka'.

To the Editor:

We appreciate the interest in our study and would like to respond to the letter entitled “Seroprevalence comparison of different varicella vaccines among Turkish children”.[1]

Choi and Kwon pointed out a significant interpretational error of seroprevalence results as seroconversion ones. However, we disagree with them due to the difference in seroprevalence and seroconversion definitions. As known, seroprevalence means the percentage of individuals who have antibodies to an infectious agent, and a seroprevalence survey estimates the rate of people in a population who may have been previously infected.[2] These two terms may have different meanings but can be used to express the same condition for chickenpox. Because, varicella is an infectious disease characterized by vesicular rashes specific to this infection. It is not challenging for the clinicians and parents to distinguish this infection from other rashes, while routine screening of asymptomatic individuals for VZV infection is currently not recommended. Therefore, we questioned all parents for having a history of vesicular rash before we included a child in this study. Another concern may be the passive transfer of the antibodies from mother to baby. It is well-known that the antibodies transferred from the mother declined at 6-month of life and have been accepted as negative at 1-year old. Besides, an asymptomatic course of varicella was not considered in both vOKA and MAV-06 groups.

Moreover, both groups had children with similar age and demographic characteristics, and both groups were asked the same questions.[3] In Choi’s letter, it was stated that antibodies were not checked before vaccination and Turkish children were positive at a rate of 5% before vaccination in another study.[4] Since both vaccine groups have the same characteristics; this should not cause a problem in comparison. In conclusion, we still think that the hypercorrect definition of this study is the comparison of seroconversion rate.

Although FAMA assay has a higher sensitivity and specificity than anti-VZT IIFT IgG we wanted to evaluate the two vaccines in our population but couldn’t do the FAMA assay.[4] The dilution of 1:10 that was used in anti-VZT IIFT IgG assay was performed according to the manufacturer’s recommendations. We would like to do a similar evaluation comparing FAMA and anti-VZT IIFT IgG in our future studies. Finally, the vaccine studies discussed in our article are scientific articles published in peer-reviewed journals.

In addition, we conduct an epidemiological study evaluating the effectiveness of MAV/06 varicella vaccine among Turkish children.