One Dose of Varicella Vaccine Does Not Prevent School Outbreaks: Is it Time for a Second Dose?

Abstract

Although disease was mostly mild, the outbreak lasted for approximately 2 months, suggesting that varicella in vaccinated persons was contagious and that 99% varicella vaccination coverage was not sufficient to prevent the outbreak. This investigation highlights several challenges related to the prevention and control of varicella outbreaks with the 1-dose varicella vaccination program and the need for further prevention of varicella through improved vaccine-induced immunity with a routine 2-dose vaccination program. The challenges include: 1-dose varicella vaccination not providing sufficient herd immunity levels to prevent outbreaks in school settings where exposure can be intense, the effective transmission of varicella among vaccinated children, and the difficulty in the diagnosis of mild cases in vaccinated persons and early recognition of outbreaks for implementing control measures. The efficacy of 2 doses of varicella vaccine compared with 1 dose was assessed in a trial conducted among healthy children who were followed for 10 years. The efficacy for 2 doses was significantly higher than for 1 dose of varicella vaccine. This higher efficacy translated into a 3.3-fold lower risk of developing varicella >42 days after vaccination in 2- vs 1-dose recipients. Of the children receiving 2 doses, 99% achieved a glycoprotein-based enzyme-linked immunosorbent assay level of > or =5 units (considered a correlate of protection) 6 weeks after vaccination compared with 86% of children who received 1 dose. The 6-week glycoprotein-based enzyme-linked immunosorbent assay level of > or =5 units has been shown to be a good surrogate for protection from natural disease. Ten years after the implementation of the varicella vaccination program, disease incidence has declined dramatically, and vaccination coverage has increased greatly. However, varicella outbreaks continue to occur among vaccinated persons. Although varicella disease among vaccinated persons is mild, they are contagious and able to sustain transmission. As a step toward better control of varicella outbreaks and to reduce the impact on schools and public health officials, in June 2005, the Advisory Committee on Immunization Practices recommended the use of a second dose of varicella vaccine in outbreak settings. Early recognition of outbreaks is important to effectively implement a 2-dose vaccination response and to prevent more cases. Although the current recommendation of providing a second dose of varicella vaccine during an outbreak offers a tool for controlling outbreaks, a routine 2-dose recommendation would be more effective at preventing cases. Based on published data on immunogenicity and efficacy of 2 doses of varicella vaccine, routine 2-dose vaccination will provide improved protection against disease and further reduce morbidity and mortality from varicella.

A varicella outbreak in a school with high one-dose vaccination coverage, Beijing, China

“…This study confirms that children vaccinated with a single-dose of varicella vaccine may both contract and transmit varicella, and high singledose varicella vaccination coverage may not provide sufficiently high population immunity to prevent outbreaks [10][11][12][13]. This study also demonstrates, as have others, that single-dose varicella vaccination is highly effective in preventing cases and mitigating the severity of breakthrough cases that occurs [9].…”

“…During the single-dose varicella vaccination era in the United States, attack rates in school settings with high and low varicella vaccination coverage differed dramatically, from 9% to 15% in schools with coverage levels higher than 95% to 55% in a school with vaccination coverage of just 45% [6,[11][12][13][14]. In China, comparisons of areas with high varicella vaccination coverage to those with low coverage or no varicella vaccination also clearly demonstrate the impact of varicella vaccination on reducing attack rates during outbreaks.…”

Impact of Vaccination on the Epidemiology of Varicella: 1995–2009

“…In addition, a mathematical model published in 1994 suggested that partial varicella vaccine coverage of the population had the potential to increase the incidence of varicella among adolescents and adults, even if it resulted in a decrease in the incidence of varicella in children. 6 Varivax [8][9][10] leading to a recommendation for a second dose of the vaccine at 4 to 6 years of age by the ACIP in 2006. 11 Recent studies have revealed that varicella incidence has declined further since implementation of the second dose 12,13 and effectiveness of the 2-dose series has been estimated to be as high as 98%, 14 confirming findings from clinical trials.…”

Seropositivity of Varicella zoster virus in vaccinated Korean children and MAV vaccine group

“…3,[12][13][14] Although this decreased the morbidity and mortality due to varicella, outbreaks were frequently reported among the vaccinated population. [15][16][17] The controversial causes of breakthrough infections were the age at vaccination, vaccine type, primary vaccine failure (not mounting protective immunity), or secondary vaccine failure (waning of protective immunity). 17,18 In response to breakthrough infections, a necessity to administer a second dose of the vaccine has emerged.…”

“…17,18 In response to breakthrough infections, a necessity to administer a second dose of the vaccine has emerged. 16,19,20 Watson reported that a second dose would provide higher antibody levels. 21 The Advisory Committee on Immunization Practices had recommended a second dose of varicella vaccine at 4-6 y of age (first dose at 12-15 months and second at 4-6 years) in the United States in 2006, 22 and the German Standing Committee on Vaccination had recommended a second dose varicella vaccine at 15-23 months of age (first dose at 11-14 months and second at 15-23 months, with a minimum 4-week interval) in Germany, in 2009.…”