Letter to the Editor: Epidemiological Comments on the Effectiveness of the Varicella Vaccine in Korea

Abstract

We read with great interest the paper by Lee et al. 1 about the effects of one-dose varicella (chickenpox) vaccination on disease severity among pediatric varicella patients in Korea, given the recent concern about the effectiveness of the varicella vaccine in Korea. 2,3 Lee et al. 1 reported that vaccinated patients (breakthrough cases) had significantly less moderate-tosevere symptoms than non-vaccinated patients, which is consistent with the existing literature from other countries. 4,5 However, we think the paper by Lee et al. 1 can inadvertently mislead the reader into believing that varicella incidence in Korea has significantly increased even after the introduction of a national varicella immunization program in 2005 and the effectiveness of the varicella vaccine has been insufficient to prevent against varicella in Korea.

Letter to the Editor: Effectiveness of the Varicella Vaccine Among Korean Children: Suggestions for Future Research

“…The authors’ finding is in strong contrast with a low level (13.0%) of varicella VE reported in a previous case-control study. 2 But it was generally in line with our position 3 , 4 based on a case-coverage simulation analysis that the real VE against varicella in the previous case-control study would have been 65–90% if selection bias would have been corrected.…”

Letter to the Editor: Effectiveness of the Varicella Vaccine in Korea: Unresolved Issues

“…However, we have found that Lee et al 1 misrepresented our simulation analysis and its results presented in our previous letter. 2 In addition, we have found that in their response, the authors were misleading to suggest that an age-shift phenomenon among varicella cases in Korea has occurred with an increasing annual incident rate of varicella after the introduction of the one-dose varicella national immunization program (NIP) in 2005. In this letter, we explicate and defend our simulation analysis that was a key basis for our position that the effectiveness of varicella vaccines in the authors' previous case-control study 3 may have been considerably underestimated.…”

“…We read with interest the response by Lee et al 1 to our previous letter 2 on the effectiveness of the varicella vaccine in Korea. However, we have found that Lee et al 1 misrepresented our simulation analysis and its results presented in our previous letter.…”

Seroprevalence comparison of different varicella vaccines among Turkish children

“…However, the case–control study has been criticized due to possible selection bias. 11–13 A recent national birth-cohort study 14 among Korean children confirmed that there is at least a moderate level (49.9–86.1%) of one-dose vaccine effectiveness against VZV, although it may have been underestimated. 11 , 13 On the other hand, the same research group 9 , 10 of the erroneous case–control study has continued to argue that the incidence rate of varicella cases in Korea has increased even after the national varicella immunization program.…”

“… 11–13 A recent national birth-cohort study 14 among Korean children confirmed that there is at least a moderate level (49.9–86.1%) of one-dose vaccine effectiveness against VZV, although it may have been underestimated. 11 , 13 On the other hand, the same research group 9 , 10 of the erroneous case–control study has continued to argue that the incidence rate of varicella cases in Korea has increased even after the national varicella immunization program. However, as we said elsewhere, 11 their argument has been based on data from the Korea National Notifiable Disease Surveillance System in which only varicella cases notified by medical doctors and other responsible persons are included and counted.…”