Pediatric deaths due to varicella are becoming a thing of the past

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ST LOUIS (MD Consult) - With implementation of the varicella vaccination program in the United States, deaths due to the disease among children and adolescents have virtually ceased, finds a study reported in the August 2011 issue of Pediatrics.

Using data from the Mortality Multiple Cause-of-Death records of the US National Center for Health Statistics, investigators analyzed temporal patterns of deaths among individuals of all ages for which varicella was listed as an underlying or contributing cause between 1990 and 2007. The vaccination program was introduced in 1995.

Over the first 12 years of the program, the annual average mortality rate for varicella listed as the underlying cause fell by 88%, from 0.41 per million population in 1990-1994 to 0.05 per million population in 2005-2007.

The same pattern was evident across all age-groups. The reduction was 97%, 90%, and 67% among children and adolescents younger than 20 years, among adults aged 20 to 49 years, and among adults aged 50 years or older, respectively.

In the last 6 years analyzed (2002-2007), there were 3 deaths each among children aged 1 to 4 years and aged 5 to 9 years; in sharp contrast, there were an average of 13 and 16 deaths annually, respectively, before the vaccine was introduced.

All of the deaths among children and adolescents younger than 20 years in 2002-2007 occurred in those who did not have high-risk conditions as strictly defined by the study, although 3 occurred in children or adolescents having conditions that could increase risk.

"The impressive decline in varicella deaths can be directly attributed to successful implementation of the 1-dose vaccination program," the investigators conclude. "With the current 2-dose program, there is potential that these most severe outcomes of a vaccine-preventable disease could be eliminated."

Pediatrics. 2011;128:214-220. 

 

• Did the varicella zoster vaccine prove to be effective long term?
• A prospective cohort study evaluated the long-term effectiveness of the vaccine, its impact on varicella and herpes zoster epidemiology, and the impact of a second dose of the vaccine.
• Long-term follow-up demonstrated that varicella vaccination was effective at preventing chicken pox and seemed to lower risk of herpes zoster over a 14-year period.

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SUMMARY

Practice Update Editorial Team

Vaccination of children for varicella zoster virus (VZV) has substantially decreased incidence of disease. Before the vaccine was licensed and recommended in the United States, VZV infection was highly prevalent, with more than 90% of people experiencing an infection by the age of 20 years. The efficacy of one dose of this medication was shown to be high in clinical trials, with a recent implementation of a second dose showing increased effectiveness in multiple studies. The overall effect of this vaccination on herpes zoster (HZ) incidence is not well understood.
In this prospective cohort study, Baxter et al aimed to assess the long-term effectiveness of the vaccine, its impact on varicella and HZ epidemiology, and the impact of the second dose, which was introduced in 2006. The study was conducted at multiple Kaiser Permanente Northern California sites and included children 12 to 23 months of age who received varicella vaccination in 1995. Consenting parents were interviewed via telephone every 6 months for 14 years, until 2009. Outcomes included breakthrough cases of varicella, number of lesions, and rates of HZ. Person-time was calculated based on the interview cycle.
The analytic cohort included 7386 patients and a total of 103,098 person-years (PY) were collected. In the 14 years after varicella vaccination, there were 1505 cases of breakthrough varicella. All cases followed the first vaccine dose. No cases of breakthrough were reported after the second dose was received. The average incidence was 15.9 cases per 1000 PY (95% CI, 15.1–16.7). This finding represented a 9 to 10 times lower rate of incidence as compared with same-aged children in the era preceding vaccination. Effectiveness was 89% to 90%, depending on the reference study. Of the 113 reported cases of HZ, 46 cases were confirmed. This finding represented an incidence rate of 0.45 per 1000 PY (95% CI, 0.33–0.60). Compared to similar children who experienced naturally acquired varicella, this finding suggested a 40% decreased incidence in those who were vaccinated.
This prospective cohort study showed, over 14 years of follow-up, varicella vaccination was effective in preventing VZV, with no evidence of waning effectiveness. Further, findings suggested a decreased incidence rate of HZ among vaccinated children as compared with unvaccinated children of the same age.

 

Long-term Effectiveness of Varicella Vaccine: A 14-Year, Prospective Cohort Study

1. Roger Baxter, MD^a,
2. Paula Ray, MPH^a,
3. Trung N. Tran, MD, PhD^b,
4. Steve Black, MD^c,
5. Henry R. Shinefield, MD^d,
6. Paul M. Coplan, ScD, MBA^e,
7. Edwin Lewis, MPH^a,
8. Bruce Fireman, MA^a, and
9. Patricia Saddier, MD, PhD^b

+ Author Affiliations

1. ^aKaiser Permanente Vaccine Study Center, Oakland, California;
2. ^bEpidemiology Department, Merck Sharp & Dohme Corp, Whitehouse Station, New Jersey;
3. ^cCenter for Global Health, Cincinnati Children’s Hospital, Cincinnati, Ohio;
4. ^dUniversity of California San Francisco Medical Center, University of California, San Francisco, San Francisco, California; and
5. ^ePurdue Pharma, Stamford, Connecticut

Abstract from Pediatrics

BACKGROUND: Varicella vaccine was licensed in the United States in 1995 for individuals ≥12 months of age. A second dose was recommended in the United States in June 2006. Varicella incidence and vaccine effectiveness were assessed in a 14-year prospective study conducted at Kaiser Permanente Northern California.

METHODS: A total of 7585 children vaccinated with varicella vaccine in their second year of life in 1995 were followed up prospectively for breakthrough varicella and herpes zoster (HZ) through 2009. A total of 2826 of these children received a second dose in 2006–2009. Incidences of varicella and HZ were estimated and compared with prevaccine era rates.

RESULTS: In this cohort of vaccinated children, the average incidence of varicella was 15.9 per 1000 person-years, nine- to tenfold lower than in the prevaccine era. Vaccine effectiveness at the end of the study period was 90%, with no indication of waning over time. Most cases of varicella were mild and occurred early after vaccination. No child developed varicella after a second dose. HZ cases were mild, and rates were lower in the cohort of vaccinated children than in unvaccinated children during the prevaccine era (relative risk: 0.61 [95% confidence interval: 0.43–0.89]).

CONCLUSIONS: This study confirmed that varicella vaccine is effective at preventing chicken pox, with no waning noted over a 14-year period. One dose provided excellent protection against moderate to severe disease, and most cases occurred shortly after the cohort was vaccinated. The study data also suggest that varicella vaccination may reduce the risks of HZ in vaccinated children.