chickenpox ( varicella ) is a highly contagious disease recognized by a characteristic and often pathognomonic maculopapular vesicular rash . varicella may lead to serious complications , including secondary bacterial skin and soft - tissue infections , cerebellitis , encephalitis , pneumonia , and coagulopathy . more than 95% of the non - vaccinated populations were infected with varicella , and most of them are younger than 20 years . children younger than 10 years of age , particularly those between 3 and 6 years , exhibit a high incidence of infection when they do not receive varicella vaccine as part of a universal vaccination program . in 1998 , the world health organization ( who ) recommended routine childhood varicella vaccination in countries where chickenpox significantly affects public health . since the introduction of universal vaccination , a number of countries have witnessed declines in varicella incidence , hospitalization , and/or mortality , including the united states of america , australia , italy , germany , and taiwan . varicella vaccination provides long - term effectiveness in preventing varicella and may reduce the risk of herpes zoster . furthermore , varicella vaccination is cost - effective in the asian regions . in singapore , the benefit  cost ratio of vaccination is 2.25 , which indicates that every us$1.00 invested in vaccination would save us$2.25 . similar findings were reported in 2 studies in taiwan , which reported a benefit  cost ratio of 2.06   and 0.9 , respectively . although varicella is a global health issue , disease burden varies by geographical region , climate , population density , and socioeconomic development . for example , the onset of varicella infection may be delayed in tropical countries because of virus inactivation by high ambient temperature and humidity . in hong kong , a city with subtropical climate , the average annual varicella notification and hospital attendance rates in children younger than 18 years are 981 and 285 per 100,000 individuals , respectively . moreover , complication rate is 47% among hospitalized cases . even though the varicella complication rate in hong kong is comparable with international data , the varicella vaccine was only introduced into hong kong 's universal childhood immunization program ( cip ) as a free but optional vaccine in july 2014 for children born on or after january 1 , 2013 . before the implementation of universal varicella vaccination , children in hong kong a survey conducted by hong kong 's department of health in 2009 reported that only 32.4% of local - born children had received varicella vaccine at the time . a 2012 survey of kindergartens revealed the varicella infection rates was 19.5% and the uptake of varicella vaccination rate was 57.6% . although varicella vaccine coverage has increased in hong kong , it remains below that of the united states ( 79.9%92.0% ) . previously noted barriers to vaccination in hong kong include uncertainties about the effectiveness and side effects of the vaccine and the lack of recommendations from doctors or the government . cross - sectional surveys conducted in the united states and turkey showed that positive parental health beliefs on the effect of varicella vaccine may affect parental decisions to vaccinate their children . however , both studies did not correlate parental health beliefs and vaccination status . in the present study , we investigate the varicella vaccination rates among preschool ( kindergarten ) and primary schoolchildren before the vaccine 's incorporation into hong kong 's universal cip ; the association between the rates and health beliefs and demographic characteristics of the parents of these children ; and the motivators and barriers of having the vaccination . a complete list of kindergarten and primary schools was downloaded from hong kong 's education bureau ( www.edb.gov.hk ) , which comprise 948 kindergartens and 615 local primary schools . fourteen kindergarten ( 1.5% ) and 5 primary schools ( 0.8% ) were randomly selected and their school principals were invited to participate . although no data are available on the age - specific varicella cumulative incidence in hong kong , several overseas studies reported varicella seroprevalence rates in children . various countries such as england , italy , australia , and korea   have varicella seroprevalence rates ranging from 58% to 75% by the age of 5 years , and 83% to 93% by the age of 12 years . from these figures , the sample size was estimated to be 1400 kindergarten students ( 350 cases for each age group within 25 years of age ) , and 1610 primary school students ( 230 cases for each age group within 612 years of age ) , which sum up to a total of 3010 students . this estimation gave a precision of 5% at a confidence interval of 95% for age - specific varicella cumulative incidence in our schoolchildren population . according to the education statistics ( www.edb.gov.hk ) and by assuming that the number of students in each kindergarten and primary school in hong kong are around 100 and 400 , respectively , we determined that 14 kindergartens and 5 primary schools can satisfy the sample size . after obtaining consent from the principals , questionnaire packages that contain information , consent forms , and self - administered questionnaires were distributed to the students . the students were then asked to bring home the packages for filling out by their respective parent or guardian . the questionnaire consisted of 4 parts : demographic information of the children and the respondents , children 's history of varicella infection and vaccination , 10 parental health belief statements regarding the varicella vaccine , knowledge on varicella transmission and therapy , and reasons / barriers for their having / not having varicella vaccination . most questions in the survey were in multiple - choice format , except for personal health beliefs and motivators / barriers for vaccination , in which participants were requested to answer with numbers in pre - specified ranges . each of the 10 parental health belief statements were scored from 1 ( completely disagree ) to 6 ( completely agree ) . the motivators / barriers of vaccination were graded using a 6-point likert scale from 0 ( completely disagree ) to 5 ( completely agree ) . only the parents of vaccinated children were asked to answer on the motivators of vaccination , whereas only the parents of unvaccinated children were asked to answer on the barriers . perceived knowledge and chance of infection were assessed by categorical responses ranging from  very inadequate / very unlikely  to  very adequate / very likely . completed questionnaires were collected , and data checking and entry into a pre - developed spss database were performed by student assistants . median and interquartile ranges were calculated by vaccination status for the variables that used the likert scale and subsequently compared by employing the mann crude odds ratios ( ors ) and their 95% confidence intervals were computed for each variable by vaccination status . ors with p values < 0.1 were entered to the multivariate logistic regression , and a stepwise procedure was used to select the final model . all analyses were conducted using spss version 20 ( spss inc , chicago , il ) . as individual schools may affect vaccination status , a school variable was added as a random factor in the regression using the approach of generalized linear mixed - effects model . a total of 5617 questionnaires were distributed , and 3484 completed questionnaires were returned , giving a response rate of 62.0% . previous history of varicella infection was noted in 20.7% ( 721 ) of the children . after excluding those with history of varicella infection and 36 with missing infection information , 2727 children were included in the succeeding analyses . among these 2727 children , 69.0% ( 1881 ) were reported to have been vaccinated against varicella , 53.2% ( 1452 ) were boys , and 91.8% ( 2503 ) were born in hong kong . furthermore , 56.2% attended kindergarten ( mean age : 4.14    0.96 years ) , 24.4% attended junior primary schools ( mean age : 7.28    0.92 years ) , and 16.7% attended senior primary schools ( mean age : 10.36    0.90 years ) . of the questionnaires , 77.9% ( 2124 ) were completed by mothers and 18.0% ( 492 ) by fathers ( table 1  ) . moreover , 94.5% of respondents indicated that they would allow their children to be vaccinated if the vaccine was included in the government 's universal cip . significant differences in vaccination rates were noted in relation to the child 's place of birth and school grade , respondent 's educational level and occupation , family income , and housing type ( table 1  ) . significant differences were also noted in perceived knowledge , perceived chance of infection , discussion with a family doctor , and willingness to pay ( table 1  ) . demographic characteristics of children and respondents ( n  =  2727 ) demographic characteristics of children and respondents ( n  =  2727 ) results of the scoring of the 10 parental health belief statements by vaccination status are presented below . among the respondents with vaccinated children , 6 statements obtained a median score of 5 , which implies that > 50% of respondents strongly agreed with these statements ( table 2 ) . for respondents with unvaccinated children , only 3 statements obtained median scores of 5 . all but one statement showed significant differences between the vaccinated and nonvaccinated groups ( table 2 ) . parental health beliefs on having their children vaccinated against varicella infection adjusted ors and their 95% confidence intervals from the logistic regression were calculated based on the final model selected using the stepwise procedure ( table 3 ) . children who were studying in senior primary school , respondents with educational attainments higher than the secondary level , family income of $40,000 , very adequate perceived knowledge on varicella , very high perceived chance of children being infected by varicella , discussion with a family doctor , and willingness to pay > $ 300 for the vaccine were associated with higher vaccination rates . except for my child may not need the chickenpox vaccine because chickenpox is only a minor illness , these health beliefs are as follows :  the chickenpox vaccine is very effective in preventing chickenpox ,   my child is very likely to contract chickenpox if he / she does not receive the vaccine ,   the chickenpox vaccine is worthwhile even if it does not provide lifelong immunity to chickenpox for my child ,  and  i am uncomfortable with the number of shots my child is receiving . the results from the application of the generalized linear mixed model with school as random effect are also presented in table 3 . multivariate analysis of the associations between demographic characteristics and the rate of varicella vaccination reasons for varicella vaccination were scored from 0 ( not important ) to 5 ( very important ) . the median scores for  recommendation by family doctors  and  recommendation by specialists  were both 5 , which implies that > 50% of respondents thought that these recommendations were very important ( table 4 ) . recommendation on tv / newspaper / magazine  obtained the lowest median score ( 3 ) among the 6 recommendations . of the parents with vaccinated children , 71.8% , 69.0% , and 45.7% rated family doctors , specialists , and the government , respectively , as very important motivators of vaccination . reported motivators for vaccination among parents of vaccinated students four statements on the barriers to varicella vaccination (  worry about adverse side effects ,   not sure about the effectiveness of the vaccine ,   no recommendation from doctors ,  and  no recommendation from the government / department of health  ) obtained the highest median scores ( 3 ) . by contrast , 4 other statements (  do nt know where to vaccinate ,   not aware of the existence of the vaccine ,   child fear of injection ,  and  child is too young  ) obtained the lowest median scores ( 0 ) , which shows that > 50% respondents thought that these factors were unimportant barriers ( table 5 ) . of the parents of unvaccinated children , 21.3% , 22.3% , 21.7% , and 26.0% rated adverse effects , uncertain effectiveness , no recommendation from doctors , and no recommendation from the government , respectively , as very important barriers to vaccination . varicella can pose serious threats of disease to fetuses , neonates , and non - immune or immunocompromised children and adults . the present study found that 69.0% of hong kong preschool and school children were reported to have received vaccination against varicella , although the vaccine was not yet included in hong kong 's cip at the time . this rate is higher than that in a similar study in hong kong reported a few years ago . the rate increase may be due to the educational campaigns conducted by the government and the discussions on including the vaccine in the cip over the recent years . the vaccine has been included as a free optional vaccine in the cip program since 2014 . hong kong 's rate of varicella vaccination appears slightly higher than those of several other countries that also do not include the vaccine in their routine immunization programs . the corresponding vaccination rates for these countries were 61.1% in athens , greece , 50% in japan , and 62.0% in shandong province , china . the higher rate of vaccination in hong kong may indicate the greater awareness or value placed on varicella prevention by hong kong parents . this study showed that parents with higher educational attainments , greater family income , greater perceived knowledge of varicella , and higher perceived chance of infection were significantly associated with positive vaccination . in the united states , higher maternal educational levels positively correlated with varicella vaccination . similarly , families with better parental educational attainments and higher family income showed greater vaccination rates in turkey and taiwan . promoting parental knowledge on vaccination is a key factor in improving immunization rates , especially in families with lower educational backgrounds and from cities with low socioeconomic ranking , as observed in israel . discussion with a family doctor is significantly associated with a greater propensity for vaccination , which indicates that an expert 's opinion importantly influences the perspective of the parents . recommendation from family doctors  and  recommendation from specialists  were the major reasons that the parents allowed their children to receive the vaccine . by contrast , other parents did not seek vaccination for their children mainly because of their lack of knowledge about the vaccine and lack of recommendation from the experts or government officials . a previous study conducted in sweden   also showed the great importance of the role of well - trained healthcare staff in providing advice and discussing measles , mumps , and rubella vaccination with concerned parents . the results may be explained by the relationship between health beliefs and other parental attitudes . the chickenpox vaccine is very effective in preventing chickenpox  and  my child may not need the chickenpox vaccine because chickenpox is only a minor illness  may be related to the perceived knowledge of parents on vaccination . parents are more willing to vaccinate their children when with adequate awareness on the effectiveness of vaccine and potential complications of varicella . my child is very likely to contract chickenpox if he / she does not receive the vaccine  may be associated with the perceived chance of children being infected . parents were more likely to allow vaccination of their children if they perceive that their children are otherwise at risk . the chickenpox vaccine is worthwhile even if it does not provide lifelong immunity to chickenpox for my child  was also associated with parental knowledge . when promoting varicella vaccination , clarifying the period of vaccine effectiveness is important . although children can not be immunized throughout their lives , long - term health benefits still encourage vaccination . surprisingly , i am uncomfortable with the number of shots my child is receiving  positively correlated with vaccination . greater awareness on the risk of infection and more knowledge on vaccination may have outweighed the discomfort parents feel while their children are being vaccinated . this explanation , however , should be justified in future studies . despite its effectiveness in preventing varicella in the united states , the varicella vaccine has not been included in the immunization program of many countries , including japan and mainland china . furthermore , our survey was completed only before varicella vaccination was added to hong kong 's cip . this immunization program is funded by the hong kong government and includes vaccines that are free of cost . the government announced in december 2012 the possible addition of the varicella vaccine to the cip , which was then launched to fruition in july 2014 . the present study indicated that 94.5% of the respondents would allow their children to be vaccinated if the vaccine was included in the cip . furthermore , high vaccination rates ( 95% ) have been reported for all other vaccines included in cip . the strength of this study lies in the large sample of > 2700 participants recruited from 14 kindergartens and 5 primary schools randomly selected across hong kong . however , an important limitation of this study is the potential for recall bias ; the vaccination status of the children reported by parents was not validated by official records . another limitation is that the number of children without varicella infection is likely less than the figure reported because of possible previous unrecognized infection . furthermore , the total of 19 schools recruited only accounted for a small proportion of all the schools in hong kong , which might limit the generalizability despite the large sample size . this suggestion could explain the greater likelihood of varicella vaccination among parents who felt uncomfortable for their children receiving more shots of vaccines , as revealed in present study . this survey has provided valuable information on the association between parental attitudes and varicella vaccination in the period before the inclusion of the vaccine to hong kong 's cip . our study suggested that to increase vaccination rates , government officials should organize more promotional activities to raise parents awareness on the inclusion of the vaccine in the cip as a free optional vaccine . once varicella vaccine is implemented as part of hong kong 's cip for a period of time and anticipated high vaccination rates are achieved , conducting a follow - up study would be valuable to demonstrate the effect of the policy change on parental attitudes and practices regarding varicella vaccination . if possible , evidence in terms of morbidity and complications could be gathered by reviewing hospital admission data to shed greater light on the general impact of the cip inclusion . in countries with universal immunization programs that still exclude the varicella vaccine , these countries do not include united states , australia , italy , germany , and taiwan , which have already been providing universal varicella vaccination . we hope to witness a future increase in the number of countries that would follow the who recommendation on including the vaccine in their routine immunization programs . among parents of hong kong preschool and schoolchildren , parental attitudes and demographic characteristics were associated with rates of varicella vaccination . as emphasized in the study , health professionals and the government play important roles in promoting varicella vaccination to the public .