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Although often dismissed as a minor childhood illness, chickenpox is potentially very serious if contracted by certain vulnerable adults, pregnant women or neonates. This Update examines the course of the illness and implications for nurses.
The varicella-zoster virus (VZV) causes chickenpox (varicella) as the primary disease and shingles (zoster) as a recurrent manifestation of infection, both being generally benign and self-limiting. While these infections may be severe in adults and even life-threatening in immunosuppressed individuals, they may be amenable to effective antiviral drugs or varicella-zoster immune globulin, provided the treatment is administered early. The prompt diagnosis of VZV infections may be accelerated by rapid, sensitive and specific molecular techniques such as amplification by polymerase chain reaction (PCR) compared with slower and more cumbersome tissue culture and serological procedures. Based on the VZV gene 4 which encodes a transcriptional activator, primers were designed for use in PCR to amplify a target fragment of 381 bp. Distinct diagnostic bands were observed by agarose gel electrophoresis of PCR products of VZV strains isolated from 11 varicella and 7 zoster patients in Singapore, as well as of the Japanese vaccine Oka strain. The detection sensitivity of this PCR assay was determined to be 1 pg of purified VZV DNA equivalent to about 7,000 viral DNA copies. No target bands were amplified from negative control templates from five related human herpes-viruses and from human DNA. The specificity of the PCR products was ensured by direct cycle DNA sequencing, which revealed complete identity of the 18 VZV isolates with the published European Dumas strain. The strong sequence conservation of the target fragment renders this PCR assay highly reliable for detecting the VZV sequence. Only one VZV strain isolated from a patient with varicella during pregnancy exhibited a GGA to GAA point mutation at codon 46 of gene 4, culminating in the non-conservative substitution of Ser with Phe. The predicted secondary structure of the mutant polypeptide portrayed a radical alteration, which may influence its function in transcriptional activation.
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The most compelling rationale for introducing universal vaccination against varicella was the predicted benefits to healthy children. Current evidence from the US experience indicates that these benefits are being realized. As is true for any new vaccine, implementation of such a program necessitates disease surveillance and modifications of the vaccine regimen as needed. In the case of VZV, the epidemiology of herpes zoster must be tracked as well as varicella disease trends. The prevention of herpes zoster may be another use of live attenuated or inactivated varicella vaccines.
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We present data to confirm that exposure to varicella boosts immunity to herpes-zoster. We show that exposure to varicella is greater in adults living with children and that this exposure is highly protective against zoster (Incidence ratio=0.75, 95% CI, 0.63-0.89). The data is used to parameterise a mathematical model of varicella zoster virus (VZV) transmission that captures differences in exposure to varicella in adults living with and without children. Under the 'best-fit' model, exposure to varicella is estimated to boost cell-mediated immunity for an average of 20 years (95% CI, 7-41years). Mass varicella vaccination is expected to cause a major epidemic of herpes-zoster, affecting more than 50% of those aged 10-44 years at the introduction of vaccination.
Cost-benefit analysis was conducted to determine whether it is worthwhile to initiate a routine varicella vaccination program in Taiwan from different perspectives. Using the human capital approach, the discounted net cost for vaccination program was New Taiwan Dollars (NTD) 281 million from health care payer's perspective. Taking indirect costs into account, the net saving due to vaccination program was NTD 425 million from the societal perspective. In terms of benefit-cost ratio, a mass varicella vaccination program could only save NTD 0.34 in discounted costs for each dollar incurred in a vaccination program from health care payer's perspective whereas save NTD 2.06 from the societal viewpoint. Results based on the willingness-to-pay (WTP) method showed the Net Present Value (NPV) of the vaccination program was estimated as -NTD 272 million. We conclude that a routine varicella vaccination program is worthwhile from the societal perspective but neither from health care payer's nor from consumer decision based on the perspective of WTP.