Detection of antibodies to varicella-zoster virus in recipients of the varicella vaccine by using a luciferase immunoprecipitation system assay.

A high-throughput test to detect varicella-zoster virus (VZV) antibodies in varicella vaccine recipients is not currently available. One of the most sensitive tests for detecting VZV antibodies after vaccination is the fluorescent antibody to membrane antigen (FAMA) test. Unfortunately, this test is labor-intensive, somewhat subjective to read, and not commercially available. Therefore, we developed a highly quantitative and high-throughput luciferase immunoprecipitation system (LIPS) assay to detect antibody to VZV glycoprotein E (gE). Tests of children who received the varicella vaccine showed that the gE LIPS assay had 90% sensitivity and 70% specificity, a viral capsid antigen enzyme-linked immunosorbent assay (ELISA) had 67% and 87% specificity, and a glycoprotein ELISA (not commercially available in the United States) had 94% sensitivity and 74% specificity compared with the FAMA test. The rates of antibody detection by the gE LIPS and glycoprotein ELISA were not statistically different. Therefore, the gE LIPS assay may be useful for detecting VZV antibodies in varicella vaccine recipients. (This study has been registered at ClinicalTrials.gov under registration no. NCT00921999.).

Effectiveness of 2 doses of varicella vaccine in children.

BACKGROUND: Because of ongoing outbreaks of varicella, a second dose of varicella vaccine was added to the routine immunization schedule for children in June 2006 by the Centers for Disease Control and Prevention. METHODS: We assessed the effectiveness of 2 doses of varicella vaccine in a case-control study by identifying children ≥4 years of age with varicella confirmed by polymerase chain reaction assay and up to 2 controls matched by age and pediatric practice. Effectiveness was calculated using exact conditional logistic regression. RESULTS: From July 2006 to January 2010, of the 71 case subjects and 140 matched controls enrolled, no cases (0%) vs 22 controls (15.7%) had received 2 doses of varicella vaccine, 66 cases (93.0%) vs 117 controls (83.6%) had received 1 dose, and 5 cases (7.0%) vs 1 control (0.7%) did not receive varicella vaccine (P < .001). The effectiveness of 2 doses of the vaccine was 98.3% (95% confidence level [CI]: 83.5%-100%; P < .001). The matched odds ratio for 2 doses vs 1 dose of the vaccine was 0.053 (95% CI: 0.002-0.320; P < .001). CONCLUSION: The effectiveness of 2 doses of varicella vaccine in the first 2.5 years after recommendation of a routine second dose of the vaccine for children is excellent. Odds of developing varicella were 95% lower for children who received 2 doses compared with 1 dose of varicella vaccine.

A phase I-II study of live attenuated varicella-zoster virus vaccine to boost immunity in human immunodeficiency virus-infected children with previous varicella.

Herpes zoster, may be severe and recurrent in HIV-infected children. We determined the safety and immunogenicity of live attenuated varicella-zoster virus (VZV) vaccine in 46 HIV-infected children who had experienced varicella. There were no serious adverse events. Two years after vaccination 82% of subjects remained VZV-antibody positive and 60% had VZV-specific cell-mediated immunity. No child developed herpes zoster.

The safety profile of varicella vaccine: a 10-year review.

Varivax (varicella virus vaccine live [Oka/Merck]; Merck), a live attenuated varicella vaccine, is indicated for vaccination against varicella in appropriate individuals > or =12 months of age. The 10-year safety profile for Varivax is described using data submitted to Merck from routine global postmarketing surveillance, combined with information from a Varicella Zoster Virus Identification Program, which uses polymerase chain reaction (PCR) analysis to identify the presence and strain of VZV in selected specimens. There were 16,683 reports worldwide voluntarily submitted to Merck, for an overall reporting rate of 3.4 reports/10,000 doses of vaccine distributed. PCR analysis of vesicular rashes that occurred within the first 2 weeks after vaccination was more likely to identify wild-type varicella-zoster virus (VZV), whereas the presence of Oka VZV was generally associated with vesicular rashes that occurred 15-42 days after vaccination. Reports of breakthrough varicella that occurred >42 days after vaccination were associated with wild-type VZV. Among 697 herpes zoster reports, PCR analysis identified Oka VZV in 57 reports and wild-type VZV in 38 reports. There were no primary neurologic adverse events associated with Oka VZV. Secondary transmission of Oka VZV from vaccine recipients with postvaccination vesicular rashes was identified in 3 susceptible household contacts. Disseminated Oka VZV was identified in 6 immunocompromised patients and 1 patient with Down syndrome. This review has shown that the vaccine is generally safe and well tolerated.

Risk of herpes zoster in adults immunized with varicella vaccine.

A program of routine varicella vaccination of children 12-18 months of age, begun in the United States in 1995, has been very successful in reducing the incidence of varicella. Varicella-zoster virus (VZV), in both wild-type and live attenuated forms, is notable for its ability to produce latent infection of sensory neurons from which it can later reactivate to cause herpes zoster (HZ). Therefore, the effects of vaccination on this secondary VZV-related disease are important to consider; in practice, however, such studies are complicated by the typically long delay between acquisition of the virus and its reactivation. Studies of immunocompromised children have shown that vaccination is relatively protective against HZ in this highly vulnerable group. We now present long-term follow-up data on a group of individuals who received varicella vaccine as healthy young adults 10-26 years ago and who have been followed prospectively by means of active surveillance. Among some 2000 person-years of follow-up, 2 cases of HZ have occurred, for a rate of 1.00 case/1000 person-years. Overall, the incidence of HZ in this cohort, therefore, is similar to published data for the US population in the prevaccine era.

Primary vaccine failure after 1 dose of varicella vaccine in healthy children.

Universal immunization of young children with 1 dose of varicella vaccine was recommended in the United States in 1995, and it has significantly decreased the incidence of chickenpox. Outbreaks of varicella, however, are reported among vaccinated children. Although vaccine effectiveness has usually been 85%, rates as low as 44% have been observed. Whether this is from primary or secondary vaccine failure-or both-is unclear. We tested serum samples from 148 healthy children immunized against varicella in New York, Tennessee, and California to determine their seroconversion rates, before and after 1 dose of Merck/Oka varicella vaccine. The median age at vaccination was 12.5 months; postvaccination serum samples were obtained on average 4 months later. Serum was tested for antibodies against varicella-zoster virus (VZV) by use of the previously validated sensitive and specific fluorescent antibody to membrane antigen (FAMA) assay. Of 148 healthy child vaccinees, 113 (76%) seroconverted, and 24% had no detectable VZV FAMA antibodies. Our data contrast with reported seroconversion rates of 86%-96% by other VZV antibody tests and suggest that many cases of varicella in immunized children are due to primary vaccine failure. A second dose of varicella vaccine is expected to increase seroconversion rates and vaccine effectiveness.

Severe varicella caused by varicella-vaccine strain in a child with significant T-cell dysfunction.

In March 1995, the US Food and Drug Administration approved a live attenuated varicella vaccine for use in healthy children 12 months to 12 years old. We report here an 18-month-old girl with cell-mediated immunodeficiency who developed a severe vaccine-associated rash and clinical evidence of vaccine-associated pneumonia 1 month after inadvertent receipt of varicella vaccine.

Natural selection for rash-forming genotypes of the varicella-zoster vaccine virus detected within immunized human hosts.

The Oka vaccine strain is a live attenuated virus that is routinely administered to children in the United States and Europe to prevent chickenpox. It is effective and safe but occasionally produces a rash. The vaccine virus has accumulated mutations during its attenuation, but the rashes are not explained by their reversion, unlike complications reported for other viral vaccines. Indeed, most of the novel mutations distinguishing the Oka vaccine from the more virulent parental virus have not actually become fixed. Because the parental alleles are still present, the vaccine is polymorphic at >30 loci and therefore contains a mixture of related viruses. The inoculation of >40 million patients has consequently created a highly replicated evolutionary experiment that we have used to assess the competitive ability of these different viral genotypes in a human host. Using virus recovered from rash vesicles, we show that two vaccine mutations, causing amino acid substitutions in the major transactivating protein IE62, are outcompeted by the ancestral alleles. Standard interpretations of varicella disease severity concentrate on the undeniably important effects of host genotype and immune status, yet our results allow us to demonstrate that the viral genotype is associated with virulence and to identify the key sites. We propose that these loci have pleiotropic effects on the immunogenic properties of the virus, rash formation, and its epidemiological spread, which mould the evolution of its virulence. These findings are of practical importance for reducing the incidence of vaccine-associated rash and promoting public acceptance of the vaccine.

Vaccine Oka varicella-zoster virus genotypes are monomorphic in single vesicles and polymorphic in respiratory tract secretions.

We previously found that, after immunization with vaccine Oka varicella-zoster virus, virus obtained from a single vesicle were monomorphic, and virus obtained from different individuals were heterogeneous. Here we show that virus obtained from the lungs of a patient were a mixture of vaccine Oka variants. We hypothesize that complications after immunization are unlikely to be caused by expansion of a single, biologically more virulent clone of virus that either pre-exists in the vaccine or develops after random mutation of different clones. We hypothesize that some clones are more trophic than others for skin.

An evaluation of single nucleotide polymorphisms used to differentiate vaccine and wild type strains of varicella-zoster virus.

Rashes following immunization with the vaccine strain (vOka) of varicella-zoster virus (VZV) may occur in up to 5% of children and 10% of adults. In 40% of cases, the causative virus is the vaccine strain and in 60% wild type virus is found. Several reports have identified three restriction site polymorphisms in ORF 62 and the loss of one in ORF 6, which differentiate vOka from wild type VZV, including the parental wild type strain from which vOka, is derived. Using polymerase chain reaction (PCR), restriction enzyme analysis, and sequencing, we analyzed the presence of these markers in the GlaxoSmithKline (GSK, UK) and Merck vaccine preparations as well as in 15 vaccine virus rashes and 15 wild type UK viruses. Our data suggest that a Sma1 positive and an Nae1 positive site in ORF 62 are present in the GSK and Merck vaccine preparations and all vaccine virus rashes. By contrast, a BssHII positive vaccine virus restriction site in ORF 62 and an Alu1 negative site in ORF 6 were mixed in the GSK and Merck vaccines and absent in some of the vaccine rashes. The BssHII site was also present in the European wild type C viruses in UK. The data suggest that unlike the Biken vaccine preparation, the Merck and GSK vaccine preparations are polymorphic for the BssHII and Alu1 restriction sites. These sites are also present variably in the vaccine viruses causing rashes following vaccination, and are therefore unreliable markers for differentiating vOka and wild type VZV strains.

Rashes occurring after immunization with a mixture of viruses in the Oka vaccine are derived from single clones of virus.

Vaccination against chickenpox causes a varicella-like rash in up to 5% of healthy children and 50% of children with leukemia. The vaccine may establish latency and reactivate to cause herpes zoster, albeit more rarely than wild-type virus. All vaccine preparations are composed of a mixture of varicella-zoster virus strains that show genotypic variation at several loci. We have shown, by DNA sequencing of 40 polymorphic loci, that viruses sampled from vesicles in varicella-like and herpes zoster rashes are single clones. This finding suggests that, between the time of inoculation of the vaccine and development of rash, selection of single strains occurs. The results have general implications for the pathogenesis of varicella-zoster virus.

Effectiveness over time of varicella vaccine.

CONTEXT: Reports of outbreaks of varicella in highly immunized groups have increased concern about the effectiveness of varicella vaccine. OBJECTIVE: To assess whether the effectiveness of varicella vaccine is affected either by time since vaccination or by age at the time of vaccination. DESIGN: Case-control study conducted from March 1997 through June 2003. SETTING: Twenty different group practices in southern Connecticut. PARTICIPANTS: Case subjects, identified by active surveillance of all practices, consisted of 339 eligible children 13 months or older who were clinically diagnosed as having chickenpox and who also had a polymerase chain reaction (PCR) test result that was positive for varicella-zoster virus DNA. For each case subject, 2 controls were selected, matched by both age and pediatric practice. MAIN OUTCOME MEASURES: The effectiveness of the vaccine, especially the effects of time since vaccination and age at the time of vaccination, adjusted for possible confounders. RESULTS: Although the adjusted overall effectiveness of the vaccine was 87% (95% confidence interval, 81%-91%; P<.001), there was a substantial difference in the vaccine's effectiveness in the first year after vaccination (97%) and in years 2 to 8 after vaccination (84%, P =.003). The vaccine's effectiveness in year 1 was substantially lower if the vaccine was administered at younger than 15 months (73%) than if it was administered at 15 months or older (99%, P =.01), although the difference in effectiveness overall for children immunized at younger than 15 months was not statistically significantly different than for those immunized at 15 months or older (81% vs 88%, P =.17). Most cases of chickenpox in vaccinees were mild. CONCLUSIONS: Although varicella vaccine is effective, its effectiveness decreases significantly after 1 year, although most cases of breakthrough disease are mild. If administered at younger than 15 months, the vaccine's effectiveness was lower in the first year after vaccination, but the difference in effectiveness was not statistically significant for subsequent years.