According to a new study published in the journal Archives of Pediatrics & Adolescent Medicine, children of parents who refuse vaccines are over eight times more likely to get chickenpox compared to fully immunized children [1]. The study, funded by the National Institute of Allergy and Infectious Diseases (NIAID), it is the first to assess the relationship between parental vaccine refusal and the risk of chickenpox in children.

Varicella zoster virus (VZV) is a virus of the herpes family that causes chickenpox in children. In adults, the virus can cause both shingles, a painful skin rash characterized by a band of blisters that wrap around the torso from the middle of the back to the chest, and postherpetic neuralgia, persistent nerve pain that occurs after skin rash and blisters heal. VZV or chickenpox is a classic childhood disease and is one of the most commonly refused childhood vaccines due to perceptions by parents and healthcare providers that it is the least severe of all vaccine-preventable diseases. More than 90% of cases occur in children less that 15 years of age, with the highest age-specific incidence occurring during the preschool and kindergarten years (ages 3 – 6) [2]. The varicella vaccine, introduced in the U.S. in 1995, has reduced the incidence of disease and hospitalizations due to chickenpox by 90% [3].

To establish the relationship between refusing vaccination and the risk of VZV infection, researchers used electronic health records of more than 86,000 children who were members of Kaiser Permanente, an integrated managed care organization, in Colorado between 1998 and 2008 to examine data on both vaccination and disease status.

They identified 343 patients with an ICD-9 (International Classification of Diseases, 9th Revision) diagnostic code of varicella infection. Patients were excluded if they met any of the following criteria:

• a history of varicella illness rather than acute infection
• diagnosis within 14 days of varicella vaccination
• diagnosis by telephone only
• reason for lack of vaccination not documented in the medical records
• medical contraindications to varicella vaccination

Thus, 133 of the 343 patients were clinically diagnosed with varicella vaccination and evaluated further. Each case was matched by age, sex and length of healthcare enrollment to 4 randomly selected controls; 39 children were excluded from this control population because they did not have immunization records. Thus, the final control population consisted of 493 children.

Among the 133 cases, seven patients (5%) had parents who refused all varicella immunizations compared to 3 (0.6%) among the controls. Parental refusal of varicella vaccination was strongly associated with medical record-verified varicella illness, resulting in an increased risk of chickenpox requiring medical care (odds ratio, 8.6) compared with children who were vaccinated. This means that children whose parents refuse varicella vaccination were 8.6 times more likely to get chickenpox compared to fully immunized children.

The percentage of attributable risk in patients whose parents refused the vaccine was 99.4%. This is the portion of cases attributable and avoidable to VZV infection, suggesting that all seven of the unvaccinated varicella cases in the study were due to vaccine refusal. According to Jason Glanz, Ph.D., an epidemiologist at Kaiser Permanente’s Institute for Health Research and lead author on the study [4]:

Varicella isn’t necessarily a mild illness, and it’s important for parents to know that choosing not to vaccinate their children not only places their child at risk for infection requiring medical care, but also places members of the community at risk. This study adds to the body of information showing that the benefits greatly outweigh the risks of this safe vaccine.

The study has several limitations: the study population was taken from a single managed healthcare plan and geographical area, which may limit the generalizability of the findings; there may be a diagnostic bias, as physicians are more likely to make a diagnosis of chickenpox in children who are unvaccinated; there was not enough statistical power to evaluate the association between vaccine refusal and varicella infection on a yearly basis; and mild cases of varicella that did not come to medical attention would have been overlooked, over- or under-estimating the effect of vaccine refusal on the risk of varicella infection.

Vaccine recommendations

The best way to prevent chickenpox is through vaccination. Universal varicella immunization has reduced annual morbidity, mortality and hospitalizations attributable to chickenpox by more than 80% [5], and reduced healthcare costs by 97% [6].

The CDC recommends the following chickenpox (varicella) vaccination schedules:

• All healthy children 12 months through 12 years of age should have two doses of chickenpox vaccine, with the first dose administered at age 12 — 15 months and the second dose at age 4 –6 years (preferably before entering pre-kindergarten, kindergarten or first grade).
• Adolescents and adults 13 years of age and older who have never had chickenpox or the vaccine should receive two doses of the varicella vaccine, administered 4 — 8 weeks apart.

The CDC recommends the shingles (varicella-zoster) vaccine (Zostavax) for all adults 60 years of age and older who have healthy immune systems. Note that Zostavax is not approved for people younger than age 60.

References

1. Glanz et al. Parental refusal of varicella vaccination and the associated risk of varicella infection in children. Arch Pediatr Adolesc Med. 2010 Jan;164(1):66-70. DOI: 10.1001/archpediatrics.2009.244
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2. Finger et al. Age-specific incidence of chickenpox. Public Health Rep. 1994 Nov-Dec;109(6):750-5.
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3. Guris et al. Changing varicella epidemiology in active surveillance sites–United States, 1995-2005. J Infect Dis. 2008 Mar 1;197 Suppl 2:S71-5.
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4. Refusing Immunizations Increases the Risk of Varicella Illness in Children, Kaiser Permanente Study Finds. Kaiser Permanente press release. 2010 Jan 4.
5. Roush SW, Murphy TV, Vaccine-Preventable Disease Table Working Group. Historical comparisons of morbidity and mortality for vaccine-preventable diseases in the United States. JAMA. 2007;298(18):2155-2163.
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6. Zhou et al. An economic analysis of the universal varicella vaccination program in the United States. J Infect Dis. 2008 Mar 1;197 Suppl 2:S156-64.
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