Live-attenuated varicella vaccine

Advances in Next-Generation Coronavirus Vaccines in Response to Future Virus Evolution

Coronavirus disease (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has spread to more than 230 countries and territories worldwide since its outbreak in late 2019. In less than three years, infection by SARS-CoV-2 has resulted in over 600 million cases of COVID-19 and over 6.4 million deaths. Vaccines have been developed with unimaginable speed, and 11 have already been approved by the World Health Organization and given Emergency Use Listing. The administration of several first-generation SARS-CoV-2 vaccines has successfully decelerated the spread of COVID-19 but not stopped it completely. In the ongoing fight against viruses, genetic mutations frequently occur in the viral genome, resulting in a decrease in vaccine-induced antibody neutralization and widespread breakthrough infection. Facing the evolution and uncertainty of SARS-CoV-2 in the future, and the possibility of the spillover of other coronaviruses to humans, the need for vaccines with a broad spectrum of antiviral variants against multiple coronaviruses is recognized. It is imperative to develop a universal coronavirus or pan-coronavirus vaccine or drug to combat the ongoing COVID-19 pandemic as well as to prevent the next coronavirus pandemic. In this review, in addition to summarizing the protective effect of approved vaccines, we systematically summarize current work on the development of vaccines aimed at suppressing multiple SARS-CoV-2 variants of concern as well as multiple coronaviruses.

Waning Effectiveness of One-dose Universal Varicella Vaccination in Korea, 2011-2018: a Propensity Score Matched National Population Cohort

BACKGROUND

Despite high coverage (~98%) of universal varicella vaccination (UVV) in the Republic of Korea since 2005, reduction in the incidence rate of varicella is not obvious. The study aimed to evaluate the vaccine effectiveness (VE) of one-dose UVV by timeline and severity of the disease.

METHODS

All children born in Korea in 2011 were included for this retrospective cohort study that analyzed insurance claims data from 2011-2018 and the varicella vaccination records in the immunization registry. Adjusted hazard ratios by Cox proportional hazard models were used to estimate the VE through propensity score matching by the month of birth, sex, healthcare utilization rate, and region.

RESULTS

Of the total 421,070 newborns in the 2011 birth cohort, 13,360 were matched for age, sex, healthcare utilization rate, and region by the propensity score matching method. A total of 55,940 (13.29%) children were diagnosed with varicella, with the incidence rate 24.2 per 1000 person-year; 13.4% of vaccinated children and 10.4% of unvaccinated children. The VE of one-dose UVV against any varicella was 86.1% (95% confidence interval [CI], 81.4-89.5) during the first year after vaccination and 49.9% (95% CI, 43.3-55.7) during the 6-year follow-up period since vaccination, resulting in a 7.2% annual decrease of VE. The overall VE for severe varicella was 66.3%. The VE of two-dose compared to one-dose was 73.4% (95% CI, 72.2-74.6).

CONCLUSION

We found lower long-term VE in one-dose vaccination and waning of effectiveness over time. Longer follow ups of the vaccinated children as well as appropriately designed studies are needed to establish the optimal strategy in preventing varicella in Korea.

Long-term study showed that vaccination protected paediatric renal transplant recipients from life-threatening varicella zoster virus

AIM

Renal transplant patients are particularly susceptible to highly contagious diseases due to their reduced immunity. We studied transplant recipients to gauge their varicella zoster virus (VZV) serology status over time and the outcome of any VZV infections.

METHOD

This retrospective study comprised 85 children who underwent renal transplants in Gothenburg, Sweden, from 1986 to 2014, at a mean age of eight (1-18) years. The children's medical records were reviewed and 47 had the VZV infection pre-transplant and 38 had been vaccinated pre-transplant. Clinical outcomes were available for 85 children and serology results for 72.

RESULTS

At transplantation, the VZV seropositivity rate was 50% in the vaccination group and 94% in the infection group and the antibody titres were significantly lower in the vaccination group (p = 0.031). During the median follow-up period of five years post-transplant, 28% of the vaccinated children and 97% of the infection group remained seropositive and the varicella infection affected eight children: one in the infection group and seven in the vaccination group. The herpes zoster was observed in two children in the infection group.

CONCLUSION

This study demonstrated that VZV vaccination protected from symptomatic infections to a lesser extent than natural infection, but provided effective protection from life-threatening disease.

Dissecting the Molecular Mechanisms of the Tropism of Varicella-Zoster Virus for Human T Cells

Studies of varicella-zoster virus (VZV) tropism for T cells support their role in viral transport to the skin during primary infection. Multiparametric single-cell mass cytometry demonstrates that, instead of preferentially infecting skin-homing T cells, VZV alters cell signaling and remodels surface proteins to enhance T cell skin trafficking. Viral proteins dispensable in skin, such as that encoded by open reading frame 66, are necessary in T cells. Interference with VZV T cell tropism may offer novel strategies for drug and vaccine design.

Advances in Epidemiological Studies of Herpes Zoster

Herpes zoster (HZ) is a varicella zoster virus (VZV) that attacks locality of nerves and skin, resulting information of clusters of blisters on the skin connected unilateral facial nerve and accompanying apparent nerve pain. Incidence ranges from 3.2 to 4.2 per 1000 populations per year in the United States. Influence factors of HZ include age, infection history with VZV, vaccination history of varicella vaccine, reduced immunocompetence, and other diseases. Current domestic studies on HZ mainly focus on clinical reports of case treatment. This study reviews advances in foreign epidemiological studies of HZ.

Varicella-zoster vaccine in the USA: success for control of disease severity, but what next?

In the period from 1990 to 1994, before the introduction of a varicella vaccine to the USA, approximately 100 deaths in otherwise healthy individuals, children and adolescents under 20 years of age, were attributable to varicella complications. The administration of a single-dose vaccine has now been widespread in the USA for nearly 10 years; however, since the effectiveness of a single dose in children under 13 years of age in an outbreak situation is approximately 80%, consideration of a second booster dose is in progress although not yet recommended. Licensure of a measles-mumps-rubella-varicella vaccine may hasten the recommendation.

Varicella rates among unvaccinated and one-dose vaccinated healthy children in Izmir, Turkey

OBJECTIVES

We aimed to determine the rate of breakthrough varicella in Turkey, a country with low varicella vaccination coverage.

METHODS

This study was conducted between April 2008 and March 2009 at the Well-Child Clinic at Ege University and pediatricians' offices. We collected information on vaccination status and varicella infection using a questionnaire. In order to elicit more details about the severity of illness, we interviewed all parents and reviewed the clinician records. Vaccination status was verified from the medical records or vaccination cards with dates.

RESULTS

A total of 2802 children were evaluated. Of these, 1683 had been vaccinated with a single dose of varicella vaccine and 1119 were unvaccinated. Among vaccinated children, 466 (27.7%) had breakthrough varicella. Vaccinated children tended to have mild varicella. However, about 25% of breakthrough cases had moderate or severe disease. Children who were vaccinated ≥ 5 years previously had a 3.7-fold higher risk of breakthrough disease than those who were vaccinated <5 years before. Vaccination at younger than 15 months of age was not significantly associated with an increased risk of breakthrough infection.

CONCLUSIONS

Breakthrough varicella is not rare in Turkey where varicella infections are common. A longer interval since vaccination may be a risk factor for developing breakthrough varicella. Children who had been vaccinated >5 years previously were at risk for breakthrough disease. A two-dose varicella vaccine policy may be needed to provide improved protection.

Herpes simplex virus 2 ICP0 mutant viruses are avirulent and immunogenic: implications for a genital herpes vaccine

Herpes simplex virus 1 (HSV-1) ICP0⁻ mutants are interferon-sensitive, avirulent, and elicit protective immunity against HSV-1 (Virol J, 2006, 3:44). If an ICP0⁻ mutant of herpes simplex virus 2 (HSV-2) exhibited similar properties, such a virus might be used to vaccinate against genital herpes. The current study was initiated to explore this possibility. Several HSV-2 ICP0⁻ mutant viruses were constructed and evaluated in terms of three parameters: i. interferon-sensitivity; ii. virulence in mice; and iii. capacity to elicit protective immunity against HSV-2. One ICP0⁻ mutant virus in particular, HSV-2 0ΔNLS, achieved an optimal balance between avirulence and immunogenicity. HSV-2 0ΔNLS was interferon-sensitive in cultured cells. HSV-2 0ΔNLS replicated to low levels in the eyes of inoculated mice, but was rapidly repressed by an innate, Stat 1-dependent host immune response. HSV-2 0ΔNLS failed to spread from sites of inoculation, and hence produced only inapparent infections. Mice inoculated with HSV-2 0ΔNLS consistently mounted an HSV-specific IgG antibody response, and were consistently protected against lethal challenge with wild-type HSV-2. Based on their avirulence and immunogenicity, we propose that HSV-2 ICP0⁻ mutant viruses merit consideration for their potential to prevent the spread of HSV-2 and genital herpes.

Varicella vaccination in pediatric kidney and liver transplantation

Reports about efficacy and safety of live-virus attenuated vaccines in patients before and after transplantation are mainly based on small patient numbers, making general recommendations for this patient population difficult. Children and adults as well as their close relatives and contact persons should be preferably immune to VZV before solid organ transplantation to avoid VZV-associated complications, thus making VZV vaccination necessary in susceptible individuals. The following literature review focused on efficacy and safety of VZV vaccination in pediatric kidney and liver transplant recipients. Review of literature also revealed that in all pediatric transplant candidates, humoral and cellular immunity against VZV should be consistently monitored to assess waning immunity under immunosuppressive treatment. This approach is desirable to estimate the risk of severe varicella disease after exposure in these patients.

Varicella-zoster virus T cell tropism and the pathogenesis of skin infection

Varicella-zoster virus (VZV) is a medically important human alphaherpesvirus that causes varicella and zoster. VZV initiates primary infection by inoculation of the respiratory mucosa. In the course of primary infection, VZV establishes a life-long persistence in sensory ganglia; VZV reactivation from latency may result in zoster in healthy and immunocompromised patients. The VZV genome has at least 70 known or predicted open reading frames (ORFs), but understanding how these gene products function in virulence is difficult because VZV is a highly human-specific pathogen. We have addressed this obstacle by investigating VZV infection of human tissue xenografts in the severe combined immunodeficiency mouse model. In studies relevant to the pathogenesis of primary VZV infection, we have examined VZV infection of human T cell (thymus/liver) and skin xenografts. This work supports a new paradigm for VZV pathogenesis in which VZV T cell tropism provides a mechanism for delivering the virus to skin. We have also shown that VZV-infected T cells transfer VZV to neurons in sensory ganglia. The construction of infectious VZV recombinants that have deletions or targeted mutations of viral genes or their promoters and the evaluation of VZV mutants in T cell and skin xenografts has revealed determinants of VZV virulence that are important for T cell and skin tropism in vivo.

Assessing the introduction of universal varicella vaccination in the Netherlands

Although varicella is seen as a benign disease in the Netherlands, about 40,000 visits to a general practitioner (GP) are made, over 200 hospital admission occur, and 2.3 persons die on average each year. Most of this burden of disease can be prevented by universal varicella childhood vaccination. Ten years after the introduction of the single-shot, single-component varicella childhood vaccination in the USA, a major reduction in hospitalization, mortality, and burden of disease has been reported. Using our recently vaccine evaluation model for the introduction of a new vaccine in our national immunization program, we have analyzed the feasibility of universal varicella vaccination by replacing the measles-mumps-rubella (MMR) vaccine with a measles-mumps-rubella-varicella (MMRV) vaccine. After structuring and reviewing the available data, two major points of uncertainty remain: (1) the influence of universal childhood vaccination on the incidence of zoster later in life; (2) the cost-effectiveness ratio for the Dutch situation. Despite these uncertainties it is clear that universal childhood vaccination will prevent most of the varicella related GP-visits, hospitalizations, and deaths.

New mosaic subgenotype of varicella-zoster virus in the USA: VZV detection and genotyping by oligonucleotide-microarray

A rapid and sensitive microarray-based method was used to distinguish the three major circulating genotypes of varicella-zoster virus (VZV). The method analyzes five variable positions located in a 447-nucleotide variable region 1 of open reading frame 22 (ORF 22r1); these single nucleotide polymorphisms (SNP) display in stably occurring patterns specific to each of the VZV genotypes established in previously published studies. Pairs of short oligonucleotide probes (oligoprobes) with sequences corresponding to all of the observed SNP were used to detect specific sequences. Fluorescently labeled ssRNA samples for hybridization with a chip were prepared by in vitro T7 polymerase driven transcription of the amplicons of ORF 22r1, followed by chemical labeling with Cy5 into RNA sample. Ratios between fluorescent hybridization signals from each pair of oligoprobes were used to assess the sequence at each SNP. We evaluated six reference VZV strains and 130 VZV clinical specimens to validate the method. The microarray method accurately identified strains isolated in the US in 2001-2002, representing all major genotypes as determined using more extensive sequence analysis, correctly assigning strains to genotypes E (81.5%), J (3%) and M (15.5%). In addition, a new M variant (M3) was identified.

New viral vaccines

Vaccination is the most effective medical intervention against diseases caused by human viral pathogens. Viral vaccines prevent or modify the severity of illness in the individual and interrupt or reduce the transmission of the pathogens to other susceptible people. Through these mechanisms, vaccines against smallpox, polio, measles and hepatitis B have had an enormous impact on world health over the last 50 years. Advances in basic virology and understanding of human immunity promise more progress in the control of human viral diseases as the 21st century begins. Some important targets, including human immunodeficiency virus, respiratory syncytial virus and hepatitis C virus present challenges that require more basic research. The purpose of this review is to highlight four new viral vaccines that have recently, or will soon demonstrate the effective translation of basic investigations into clinical benefits for disease control in healthy and high-risk populations. These vaccines include the live attenuated vaccines against the RNA viruses, rotavirus and influenza A and B, and vaccines against human papilloma virus and varicella-zoster virus, which are DNA viruses that cause morbidity and mortality through their capacity to establish persistent infection. Although only the influenza vaccine has been licensed in the United States, these other new tools for disease prevention are likely to be introduced within the next few years, with profound effects on the diseases that they cause. Hence, as Virology celebrates its 50th anniversary, it is appropriate to examine these examples of recent advances in viral vaccines.

Disparities in varicella vaccine coverage in the absence of public funding

Varicella vaccine has been licensed in Canada since December 1998 but not provided free in all provinces. Through a cross-sectional telephone survey to a random sample of parents, we assessed factors associated with varicella vaccine uptake in the absence of public funding. Parents of children aged 2-3 years (Group I) and 6-7 years (Group II) were contacted between March and May 2003 in British Columbia, Canada. Response rate was 82% (Group I=571; Group II=704). Among susceptible children, varicella vaccine coverage was 21% (95% CI 18-25%) and 28% (95% CI 22-33%), respectively. There were significant disparities in vaccine coverage based on income and residence. Physician or nurse recommendation was a strong determinant of vaccine uptake as were belief in the safety and efficacy of vaccine. Among parents of susceptible children, 59% (343/582) would vaccinate their child if it were provided free; 25% (148/582) were undecided.

Analysis of varicella zoster virus attenuation by evaluation of chimeric parent Oka/vaccine Oka recombinant viruses in skin xenografts in the SCIDhu mouse model

Varicella-zoster virus (VZV) is the only human herpes virus for which a vaccine has been licensed. A clinical VZV isolate, designated the parent Oka (pOka) strain was passed in human and non-human fibroblasts to produce vaccine Oka (vOka). The pOka and vOka viruses exhibit similar infectivity in cultured cells but healthy susceptible individuals given vaccines derived from vOka rarely develop the cutaneous vesicular lesions characteristic of varicella. Inoculation of skin xenografts in the SCIDhu mouse model of VZV pathogenesis demonstrated that vOka had a reduced capacity to replicate in differentiated human epidermal cells in vivo (Moffat, J.F., Zerboni, L., Kinchington, P.R., Grose, C., Kaneshima, H., Arvin A.M., 1998a. Attenuation of the vaccine Oka strain of varicella-zoster virus and role of glycoprotein C in alphaherpesvirus virulence demonstrated in the SCID-hu mouse. J Virol. 72:965-74). In order to investigate the attenuation of vOka in skin, we made chimeric pOka and vOka recombinant viruses from VZV cosmids. Six chimeric pOka/vOka viruses were generated using cosmid sets that incorporate linear overlapping fragments of VZV DNA from cells infected with pOka or vOka. The cosmid sets consist of pOka and vOka DNA segments that have identical restriction sites. As expected, the growth kinetics and plaque morphologies of the six chimeric pOka/vOka viruses were indistinguishable in vitro. However, the chimeric viruses exhibited varying capacities to replicate when evaluated in skin xenografts in vivo. The presence of ORFs 30-55 from the pOka genome was sufficient to maintain wild-type infectivity in skin. Chimeric viruses containing different vOka components retained the attenuation phenotype, suggesting that vOka attenuation is multi-factorial and can be produced by genes from different regions of the vOka genome.

Seroprevalence of antibodies against varicella-zoster virus and response to the varicella vaccine in pediatric renal transplant patients

The severity of varicella-zoster virus (VZV) in immunocompromised children, especially in those receiving renal transplants, is well known. However, the use of live attenuated virus vaccine in this population is controversial. This study aimed to: (i) assess the immunization status of pediatric renal transplant recipients at our center; (ii) determine the anti-VZV antibody titers in such patients; (iii) evaluate the response to VZV vaccine in seronegative children and in those who present low antibody titers (defined as <500 mAU/mL). Vaccinated children were monitored for adverse effects for 8 wk after vaccination. Fifty patients with a mean age of 13.7 yr (range, 3-17 yr) were enrolled. In 49, blood samples were collected and antibodies were screened using ELISA. Seropositivity to VZV was found in 43 (88%), and antibody titers were >/=500 mAU/mL in 37 (75.5%). Of the 12 children who were eligible for vaccination and had antibody titers <500 mAU/mL, one developed varicella before vaccination, two did not meet the inclusion criteria, and three parents refused the vaccination. In the six vaccinated children, there were no adverse reactions to the vaccine, and four (66.6%) responded with anti-VZV titers >/=500 mAU/mL 6-8 wk after vaccination. In conclusion, after renal transplantation, varicella vaccine is safe with a 66% rate of conversion to high antibody titers.

Recurrent papular urticaria after varicella immunization in a fifteen-month-old girl

Varicella-like rash after immunization with the live attenuated varicella vaccine is relatively common. Such vaccine-associated rashes generally consist of fewer lesions than occur in chickenpox. We describe a 15-month-old girl who experienced the onset of recurring papular urticaria after varicella immunization. The rash was varicella-like and thought by us to be caused by vaccine virus.

Preventing varicella-zoster disease

Varicella-zoster virus (VZV), the cause of chickenpox and shingles, is a pathogen in retreat following the introduction of mass vaccination in the United States in 1995. The live attenuated Oka vaccine, which is safe and immunogenic, gives good protection against both varicella and zoster in the short to medium term. It has undoubtedly been highly effective to date in reducing all forms of varicella, especially severe disease. However, the huge pool of latent wild-type virus in the population represents a continuing threat. Both the biology and the epidemiology of VZV disease suggest that new vaccination strategies will be required over time.

Consensus: varicella vaccination of healthy children--a challenge for Europe

The seriousness of varicella-zoster virus (VZV) infection as a public health issue is becoming clearer as country-specific epidemiologic and pharmacoeconomic data become available. In Germany, for example, studies have shown that >5.5% of immunologically healthy individuals develop varicella-related complications such as bacterial superinfections, acute neurologic disorders, pneumonia, bronchitis and otitis media; whereas in Italy, 3.5 to 5% of childhood cases of varicella cause complications such as upper respiratory tract and cutaneous infections. Varicella vaccines are now available. These live attenuated Oka strain vaccines have been shown in extensive studies to be highly immunogenic and well-tolerated in immunocompetent and immunocompromised children, with seroconversion rates ranging from 94 to 100% and 53 to 100%, respectively. These vaccines are also highly effective against clinical disease. These considerations led to a reevaluation of varicella vaccination policies. A routine varicella vaccination program targeting healthy children has already been implemented in the US, and data produced are encouraging and valuable. Similar strategies have not yet been adopted across Europe. The European Working Group on Varicella (EuroVar) was formed in 1998 to address the issues surrounding varicella epidemiology in Europe. After a series of meetings, the EuroVar members prepared a consensus statement recommending routine varicella vaccination for all healthy children between 12 and 18 months and to all susceptible children before their 13th birthday, in addition to catch-up vaccination in older children and adults who have no reliable history of varicella and who are at high risk of transmission and exposure. However, such a policy is recommended only if a very high coverage rate can be achieved. This could be reached with a measles-mumps-rubella-varicella combined vaccine.

Use of a computerized database to study the effectiveness of an attenuated varicella vaccine

BACKGROUND

The varicella vaccine Varilrix (GlaxoSmithKline) was introduced in Israel in June 2000 as an optional vaccination for children.

METHODS

We used the database of a single health maintenance organization that serves 25% of the population in Israel to assess the effectiveness of the vaccine retrospectively. Incidence and complications of varicella were derived from the database from January 1, 1998 until December 31, 2002.

RESULTS

Since licensure >30000 individuals younger than 10 years in this health maintenance organization have been immunized with the vaccine. Annual incidence of disease per 1000 in the study population was 86.6 in 1998, 74.6 in 1999, 74.0 in 2000, 37.1 in 2001 and 44.6 in 2002. This declining trend in incidence of disease was statistically significant. Complications of varicella occurred in approximately 1% of patients throughout the 5-year study period, but there was a parallel decline in the number of patients with complications corresponding to the decline in disease incidence. Vaccine effectiveness for prevention of clinical disease in this population was 92% (95% confidence interval, 91.0 to 92.7). There were varying rates of utilization within communities of varied socioeconomic class, so that in the higher socioeconomic class there was an increased utilization and a corresponding decrease of attack rate; whereas in communities where there were lower utilization rates, corresponding increased numbers of varicella cases were seen.

CONCLUSION

This database enables long term follow-up of the effectiveness of this vaccine in a large population.

A look at the pediatrician as parent: experiences with the introduction of varicella vaccine

Many physicians voiced reservations about routine use of the varicella vaccine for healthy children after its licensing in 1995. Anecdotal evidence suggested that some pediatricians who were parents themselves were electing not to vaccinate their own children against chickenpox. Little has been written about pediatrician-parents' behaviors in caring for their own children, and how these practices may differ from the behavior that these same pediatricians apply in practice. Pediatricians' tacit attitudes toward medical interventions might be better understood from their behaviors as parents than from their clinical practices, which may be influenced by a sense of responsibility to follow guidelines of professional organizations. Varicella vaccination practices were examined to determine whether pediatricians' behaviors in parenting their own children differed from their recommendations for their patients. A mail survey was sent to 1,762 New York State pediatricians selected randomly from the membership directory of the American Academy of Pediatrics. The response rate was 43% (764/1,762); 63% of responding pediatricians were parents. Eighty-five percent of pediatricians recommended varicella vaccine routinely in practice. Of the pediatricians' own eligible children, 88% (256/291) had been vaccinated against chickenpox. We found a high overall rate of compliance with recommendations for routine use of varicella vaccine. Pediatricians who were parents were just as likely as nonparent pediatricians to recommend the vaccine routinely for their patients. Importantly, pediatrician-parents demonstrated no "double standard"; at the time of the study, 88% of pediatricians' own eligible children had been vaccinated against varicella.

Treatment and prevention of postherpetic neuralgia

There have been 4 recent major advances in the treatment of postherpetic neuralgia (PHN) that are based on the results of randomized, controlled trials. These advances are the demonstrations that gabapentin, the lidocaine patch 5%, and opioid analgesics are efficacious in patients with PHN, and the report that nortriptyline and amitriptyline provide equivalent analgesic benefits for patients with PHN but that nortriptyline is better tolerated. The results of these clinical trials are briefly reviewed, and their implications for the treatment of patients with PHN are discussed. Despite these treatment advances, many patients remain refractory to current therapy, and the prevention of PHN has therefore become an important focus of current research. Research on administration of the varicella-zoster vaccine to prevent herpes zoster and on treatment of patients who have herpes zoster with combined antiviral and analgesic therapy to prevent PHN is discussed.

Varicella and paediatric staff: current practice and vaccine cost-effectiveness

This study was undertaken to audit staff varicella policy for UK paediatric centres, and to estimate the cost-effectiveness of implementing a staff varicella vaccine policy. A telephone survey of 22 hospitals was performed to determine the policy regarding varicella immune status among healthcare workers (HCWs). All hospitals surveyed except one recorded immune status of informed HCWs, and had a policy of exclusion from work if they developed chickenpox. The total cost of vaccine implementation for nurses at the John Radcliffe Hospital neonatal unit over 5 years was estimated at 1601 pounds sterling versus 2474 pounds sterling for the estimated total cost of varicella exposure. Therefore it is likely that vaccination represents a cost-effective intervention.

Novel agents and strategies to treat herpes simplex virus infections

The quiet pandemic of herpes simplex virus (HSV) infection has plagued humanity since ancient times, causing mucocutaneous infection, such as herpes labialis and herpes genitalis. Disease symptoms often interfere with everyday activities and occasionally HSV infections are the cause of life-threatening or sight-impairing disease, especially in neonates and the immunocompromised patient population. After primary or initial infection the virus persists for life in a latent form in neurons of the host, periodically reactivating and often resulting in significant psychosocial distress for the patient. Currently, no cure is available. In the mid-1950s the first antiviral, idoxuridine, was developed for topical treatment of herpes disease and, in 1978, vidarabine was licensed for systemic use to treat HSV encephalitis. Acyclovir (Zovirax), a potent, specific and tolerable nucleosidic inhibitor of the herpes DNA polymerase, was a milestone in the development of antiviral drugs in the late 1970s. In the mid-1990s, when acyclovir became a generic drug, valacyclovir (Valtrex) and famciclovir (Famvir), prodrugs of the gold standard and penciclovir (Denavir), Vectavir), a close analogue, were launched. Though numerous approaches and strategies were tested and considerable effort was expended in the search of the next generation of an antiherpetic therapy, it proved difficult to outperform acyclovir. Notable in this regard was the award of a Nobel Prize in 1988 for the elucidation of mechanistic principles which resulted in the development of new drugs such as acyclovir. Vaccines, interleukins, interferons, therapeutic proteins, antibodies, immunomodulators and small-molecule drugs with specific or nonspecific modes of action lacked either efficacy or the required safety profile to replace the nucleosidic drugs acyclovir, valacyclovir, penciclovir and famciclovir as the first choice of treatment. Recently though, new inhibitors of the HSV helicase-primase with potent in vitro antiherpes activity, novel mechanisms of action, low resistance rates and superior efficacy against HSV in animal models have been discovered. This review summarises the current therapeutic options, discusses the potential of preclinical or investigational drugs and provides an up-to-date interpretation of the challenge to establish novel treatments for herpes simplex disease.

Use of an inactivated varicella vaccine in recipients of hematopoietic-cell transplants

BACKGROUND

The reactivation of varicella-zoster virus from latency causes zoster and is common among recipients of hematopoietic-cell transplants.

METHODS

We randomly assigned patients who were scheduled to undergo autologous hematopoietic-cell transplantation for non-Hodgkin's or Hodgkin's lymphoma to receive varicella vaccine or no vaccine. Heat-inactivated, live attenuated varicella vaccine was given within 30 days before transplantation and 30, 60, and 90 days after transplantation. The patients were monitored for zoster and for immunity against varicella-zoster virus for 12 months.

RESULTS

Of the 119 patients enrolled, 111 received a transplant. Zoster developed in 7 of 53 vaccinated patients (13 percent) and in 19 of 58 unvaccinated patients (33 percent) (P=0.01). After two patients in whom zoster developed before transplantation were excluded, the respective rates were 13 percent and 30 percent (P=0.02). In vitro CD4 T-cell proliferation in response to varicella-zoster virus (expressed as the mean stimulation index) was greater in patients who received the vaccine than in those who did not at 90 days, after three doses (P=0.04); at 120 days, after all four doses (P<0.001); at 6 months (P=0.004); and at 12 months (P=0.02). The risk of zoster was reduced for each unit increase in the stimulation index above 1.6; a stimulation index above 5.0 correlated with greater than 93 percent protection. Induration, erythema, or local pain at the injection site was observed in association with 10 percent of the doses.

CONCLUSIONS

Inactivated varicella vaccine given before hematopoietic-cell transplantation and during the first 90 days thereafter reduces the risk of zoster. The protection correlates with reconstitution of CD4 T-cell immunity against varicella-zoster virus.

Varicella: a vaccine preventable disease?

OBJECTIVES

To present a review of varicella disease, vaccine development and implementation of universal vaccination, discuss common questions about the vaccine and the epidemiology of the disease since licensure of the varicella vaccine.

METHODS

Review the incidence of complications from varicella disease prior to vaccine licensure, safety of the varicella vaccine from clinical trials and post-marketing surveillance data, the impact of the vaccine on disease incidence where high vaccine coverage has been achieved, and address some barriers to vaccination. Raise issues that developed since 1995.

RESULTS

The safety data gathered during the 20-year-gestation period of this vaccine prior to licensure has been confirmed. The vaccine works-in areas where vaccine coverage is over 70%, there has been a decline in disease, most marked in the age group with the best vaccine coverage (the 1-4-year olds), leading to a concern that unexposed susceptible children may reach adulthood and remain susceptible unless better practice of universal vaccination of ALL susceptible is practiced.

CONCLUSIONS

Varicella disease has declined in areas with moderate vaccine coverage. Continued implementation of existing vaccine policies will lead to further reductions of varicella morbidity and mortality throughout the USA.