Acceptance of varicella vaccination

ABSTRACT

Varicella is a common vaccine-preventable disease that usually presents in children as a mild infection; however, severe complications also occur. The burden of varicella is significant in the terms of incidence, complication, and hospitalization rate related to varicella and economic disease burden. Despite the evidence of overall positive effects of varicella vaccination, there are great differences in the implementation of varicella vaccination and in the uptake of the vaccine from country to country. Improving acceptance of varicella vaccination on the national and on the individual level would decrease the burden of the disease on the health of children and on health-care resources. In studies determining factors of parental acceptance of varicella vaccination questions specific for varicella vaccination were highlighted. Addressing these issues with open, evidence based communication is important to improve and maintain the trust of the public in varicella vaccination.

KEYWORDS:

• Varicella vaccination
• chickenpox
• routine vaccination
• vaccine hesitancy
• vaccine acceptance

Introduction

Varicella is a common vaccine-preventable infection caused by the varicella-zoster virus (VZV). Primary infection, also known as chickenpox, mainly affects children and presents with a vesicular pruritic rash. Usually, the disease is self-limiting; however, it may lead to severe complications as skin and soft tissue infection, viral pneumonia, and encephalitis, even in immunocompetent people.¹

Since the development of live-attenuated varicella vaccine by Takahashi in 1974, the vaccine became widely available all over the world.¹ Effectivity of varicella vaccination has been proven in many studies.^2,3 According to the experience of countries with universal childhood varicella immunization policies, vaccination reduces varicella morbidity, complication, and hospitalization rate, decreases the incidence of herpes zoster and induces herd immunity.^4–7

World Health Organization (WHO) recommends the introduction of varicella vaccination in the routine childhood immunization schedule in countries where varicella is an important public health burden and resources are sufficient to ensure reaching and sustaining vaccine coverage ≥80%.⁸ The burden of VZV infection is definitely significant: in 2014, the WHO estimated that approximately 4.2 million severe complications leading to hospitalization and 4200 related death occur globally each year.⁹ Economic disease burden, healthcare resource utilization, and work loss related to varicella infection are also substantial, as described in studies and reviews for Europe,^6,10–13 for the Middle East,¹⁴ for Latin America and the Caribbean,^15,16 and for the Asia-Pacific region.¹⁷

Despite the evidence of overall positive effects of varicella vaccination, there are great differences in the implementation of varicella vaccination and in the uptake of the vaccine from country to country.

As vaccination stands at the intersection between the individual and the society;¹⁸ the need, the benefits, and the responsibilities regarding vaccination arise at these two levels: the level of the society, represented by the national health-care governments of countries, and at the level of the individuals deciding pro or contra on taking the vaccination. Varicella vaccination rate, and as a result varicella disease burden, incidence, and number of complications lay on these two pillars: decision on varicella vaccination on national and on individual level.

Acceptance of varicella vaccination on national level

In 2018, varicella vaccination was recommended in 34 predominantly high-income countries, including Australia, Argentina, Brazil, Canada, Germany, Japan, Mexico, Saudi Arabia, Turkey, and the United States.^3,19 As of 2020, varicella vaccination is universally recommended in 12 European countries, of which 9 implemented publicly founded universal varicella vaccination (UVV) programs.^20,21 In the recent years, new countries have adopted UVV: after the introduction of varicella vaccination in the immunization program in Finland in 2017, UVV was most recently introduced in Hungary and Iceland, with 2-dose schedules in both countries.^11,21–23 In Hungary, budget financed mandatory UVV is available since 2019 and varicella vaccination is given at 13 and 16 months of age, separately from MMR vaccination, whereas in Iceland varicella vaccination is given together with other vaccines at the age of 12 and 18 months, from the beginning of 2020. Other countries recommend varicella vaccination to selected risk groups only or as a post-exposure prophylaxis.²¹ In some of them, the opinion on UVV seems to be changed: for example, the UK adopted a selective program; however, UVV is now being reconsidered in the country based on positive experiences with the vaccination elsewhere, and on the availability of zoster vaccination.²⁴

Despite the significant global burden of the disease and the well-established efficacy and effectiveness of the vaccine, many countries still do not routinely vaccinate against VZV.²⁵

Until the varicella vaccine is included in the routine childhood vaccination schedule, uptake of the vaccine will remain lower than ideal, and is more affected by factors influencing parents’ decision regarding vaccination. Vaccines not included in the routine schedule are less likely to be seen as important ones by parents. Even among parents not opposing vaccination altogether, there is a big difference between parents with an ‘active demand’ for vaccines, and those ‘passively accepting’ them.²⁶ Parents actively seeking vaccination labeled as ”immunization advocates” accounted for 33% of the parents in the study by Gust et al.²⁷ Vaccination rate for available but not actively recommended vaccines is generally much lower compared to the vaccines included in the schedule. In Hungary, before the introduction of UVV, the varicella vaccination rate was below 20%, compared to the >99% vaccination rate for all vaccines in the childhood vaccination schedule.²³ In Poland DTP3 coverage (98%) significantly exceeds coverage rates for vaccines not included in the routine schedule, as varicella (4.2%), pneumococcus (36.4%), or rotavirus (12.7%).²⁸ Cost of vaccination and whether parents or the state reimburse the vaccination of children may play an important role in this difference. For example, a US study found an association between state financing policy and uptake of pneumococcal conjugate vaccine.²⁹ The introduction and financing of national immunization programs against varicella would decrease the burden of varicella on the individual patients and on the health-care resources globally.

Acceptance of varicella vaccination at individual level

In countries where varicella vaccination is not included in the routine childhood vaccination schedule, uptake of varicella vaccine relies mostly on the intention of parents to vaccinate. Public acceptance of vaccines is impaired by vaccine hesitancy, recognized as one of the top 10 threats to global health by WHO in 2019.³⁰ According to WHO/UNICEF data, the three main reasons given for vaccine hesitancy were: 1) risk–benefit concerns; 2) lack of knowledge and awareness on vaccination and its importance, and 3) religion, culture, gender, and socioeconomic issues regarding vaccination.³¹

Determinants of varicella vaccine acceptance were examined in several studies and according to these, the most important factors associated with varicella vaccination were the recommendation of this vaccination by the physician, and the perception of varicella as a severe enough disease to deem vaccination important.^23,32–36 Moreover, besides the general determinants of vaccine acceptance that apply to the uptake of all childhood vaccines, these studies have highlighted a few aspects that are more unique for the parental acceptance of varicella vaccination.

“It wasn’t that bad” – the role of personal experience

For most vaccine-preventable diseases, many parents today may lack awareness of danger: since they have not personally seen the devastating effect of tetanus, measles, pertussis, or poliomyelitis, some of them do not consider vaccination against these diseases important enough. This is not the case for varicella, as most parents had varicella as a child and/or have seen the disease in others. However, this factor may backfire for the acceptance of varicella vaccination. If parents remember chickenpox as a mild infection and if they have learned to accept chickenpox as a normal part of childhood it can undermine their willingness to vaccinate their children against it. Acceptance of varicella vaccination is much higher in those parents and health-care workers, who consider varicella a severe infection and who have seen complications of VZV infection.^23,33 Raising awareness in parents reluctant to vaccinate against varicella that not all cases of the infection are mild may help them to reconsider their decision. The availability of disease burden data and system for reporting varicella rates varies from country to country, contributing to low burden perception.²¹ Varicella-related hospitalization rate without UVV ranges from 9 per 100,000 in Sweden to 75 per 100,000 in France³⁷ and most of the complications develop in previously healthy children.³⁸ Improving knowledge about the burden of the disease likely increases vaccine acceptance and uptake.

“Does it really work?” – the case of breakthrough varicella

Concerns regarding the efficacy of vaccines are always mentioned among the reasons for vaccine hesitancy. For varicella vaccination cases of breakthrough varicella are often erroneously seen by parents as proof of lack of effectivity of the vaccine. In our survey, 50% of the parents who vaccinated their first child, but did not vaccine, or do not plan to vaccine their next child(ren) against varicella stated that they lost trust in the vaccine because their first child got varicella despite being vaccinated.²³ To maintain the trust of the public in varicella vaccination, open communication upon vaccination on the expected effect of the vaccination is crucial: the vaccine does not provide 100% protection from the wild virus, vaccine effectiveness is 99.4% against severe varicella after one dose, and 92% after 2 doses against all varicella – in 8% of the children immunized with 2 doses mild infections may occur.²

“For how long does it work?” – the long-term effect of varicella vaccination

When deciding on childhood vaccination, parents rarely consider the length of protection provided by the vaccine against the given disease; efficient ‘for-now’ protection from childhood infections seems to be the expectation from vaccines. In our survey, we have found that for varicella vaccination some parents consider protection until the reproductive age an important question, and have concerns about whether the vaccine will provide immunity not just to prevent childhood infections, but also to prevent the acquisition of varicella during a future pregnancy of their child.²³ This concern is not typical for other vaccines and raises a valid question regarding longevity of immunity in varicella-vaccinated individuals. According to a study on US air force recruits, chickenpox disease induces longer-lasting seropositivity compared to varicella vaccination and anti-VZV seroprevalence decreases below 80% 5 years after vaccination.³⁹ Other papers have not entirely confirmed these findings. In another study the authors have found a higher level of VZV-specific CD4 T cells in chickenpox infected individuals, but no differences in the mean antibody levels after a mean of 17 years of vaccination or withstanding the disease.⁴⁰ Other authors have described the presence of VZV-specific plasma cells and CD4 T cells in the bone marrow in all of their varicella-vaccinated subjects up to 20 years after their last VZV vaccination.⁴¹ Measurement of serum IgG titers alone may not accurately reflect vaccine protection and VZV antibody assays may differ in their ability to reliably detect vaccine seroconversion.^42,43 According to a systematic literature review, severe varicella breakthrough infections occur mostly within 5 years of vaccination, in children rather than adults; none of the cases developed during pregnancy, and all the breakthrough varicella cases spreading to organs other than the skin developed in one-dose vaccinees.⁴⁴ Concerns that widespread vaccination may result in a shift of the infection toward older individuals, partly owing to VZV reactivation, were not confirmed so far.^3,21 According to the 22 year review of the post-marketing safety data of the live varicella vaccine, after >212 million doses distributed globally, breakthrough cases of immunocompetent patients were rare and developed in children of 3–16 ages rather than in adults.⁴⁵ The risk of developing herpes zoster among vaccinated people is significantly lower compared to children who had natural chickenpox infection.²¹ The 2-dose schedule seems to establish effective and long-lasting humoral and cellular immunity.²¹

According to studies evaluating factors contributing to a parental decision on the acceptance of varicella vaccination, the most important determinant was the recommendation of the vaccine by a physician.^23,34,36

Pediatric health-care providers have an unparalleled role as ‘advocates for immunization’ in ensuring better vaccination rates of children. Pediatricians are the most trusted sources of parents on immunization, and this trust is not only based on the information they provide.^23,26,46 Trust is also based on their personal relationship making the ‘leap of faith’ to accept vaccination despite their potential uncertainties possible.^26,47 The way health-care professionals communicate about immunization plays an important role in building trust toward vaccination. Understanding, respecting, and addressing the concerns of parents, using motivational interviewing techniques and best communication practices are described to be successful in increasing vaccine acceptance at the individual level.^46,48,49

Conclusions

Experiences of countries with UVV have shown the beneficial effect of varicella vaccination on varicella incidence, hospitalization, and complication rate, economic disease burden, and mortality. Varicella vaccination is an important step in the improvement of public health. Effective communication grounded on evidence-based data, addressing the concerns related to varicella vaccination to the general public, to health-care providers, and to representatives of the health-care government of countries could increase acceptance of varicella vaccine at the national and individual level.

Disclosure of potential conflicts of interest

No potential conflicts of interest were disclosed.