Varicella: to vaccinate or not to vaccinate?

A chimeric Sindbis-based vaccine protects cynomolgus macaques against a lethal aerosol challenge of eastern equine encephalitis virus

Eastern equine encephalitis virus (EEEV) is a mosquito-borne alphavirus that causes sporadic, often fatal disease outbreaks in humans and equids, and is also a biological threat agent. Two chimeric vaccine candidates were constructed using a cDNA clone with a Sindbis virus (SINV) backbone and structural protein genes from either a North (SIN/NAEEEV) or South American (SIN/SAEEEV) strain of EEEV. The vaccine candidates were tested in a nonhuman primate (NHP) model of eastern equine encephalitis (EEE). Cynomolgus macaques were either sham-vaccinated, or vaccinated with a single dose of either SIN/NAEEEV or SIN/SAEEEV. After vaccination, animals were challenged by aerosol with a virulent North American strain of EEEV (NA EEEV). The SIN/NAEEEV vaccine provided significant protection, and most vaccinated animals survived EEEV challenge (82%) with little evidence of disease, whereas most SIN/SAEEEV-vaccinated (83%) and control (100%) animals died. Protected animals exhibited minimal changes in temperature and cardiovascular rhythm, whereas unprotected animals showed profound hyperthermia and changes in heart rate postexposure. Acute inflammation and neuronal necrosis were consistent with EEEV-induced encephalitis in unprotected animals, whereas no encephalitis-related histopathologic changes were observed in the SIN/NAEEEV-vaccinated animals. These results demonstrate that the chimeric SIN/NAEEEV vaccine candidate protects against an aerosol EEEV exposure.

Chickenpox infection after renal transplantation

BACKGROUND

Chicken pox, although a common infection among children, is rare in immunocompromised patients, particularly renal transplant recipients, and carries a very high incidence of morbidity and mortality There is little data on chickenpox in adult renal transplant recipients, although reports have suggested that it may follow a virulent course requiring frequent hospitalization, and in severe cases can cause death.

AIMS

To evaluate the incidence, severity and complications of a varicella/chickenpox infection in renal transplant recipients over 10 years follow-up.

RESULTS

An incidence of 1.48% of our patients were diagnosed with varicella infection during this 10-year period from June 2000 to June 2010 in our live-related renal transplant program, with a median patient age of 39 years (range 21-54 years). Graft dysfunction was observed among five patients following the infection, two of whom became dialysis-dependent. The other three had mild graft dysfunction from which they subsequently recovered, suggesting that infection was responsible for graft dysfunction. None of them developed rejection following exposure or with modification of immunosuppression. All of our patients required admission with 47.8% presenting with various presentations, with orchitis, pancreatitis, encephalitis and gastritis each affecting 8.6% of the patients. All patients were managed with intravenous acyclovir for 2 weeks followed by oral acyclovir for 3 months. The infection was associated with an increased mortality of 13.4% due to superadded infections and central nervous system involvement in one patient with fatal bilateral pneumonia.

CONCLUSIONS

This infection, which is a benign disease with a largely stable course among the general population, can have severe outcomes for immunocompromised patients, accounting for almost 90% with significant morbidity and mortality in the 8.6% of infected patients, thus highlighting the importance of pre-transplant vaccination in this subgroup of the population.

Uptake of varicella vaccination among young children in the United States: a success story in eliminating racial and ethnic disparities

OBJECTIVE

To examine uptake of varicella vaccine, a live attenuated vaccine licensed in 1995 and recommended in 1996 for routine vaccination of US children 12 to 18 months of age.

METHODS

Data were for 178,616 children (19-35 months of age) and were collected in the 1997 to 2004 National Immunization Survey. The main outcome measures were estimated varicella vaccine coverage from 1997 to 2004, coverage among susceptible children (ie, those without a history of varicella disease), racial/ethnic disparities, risk factors for nonvaccination, missed opportunities to vaccinate simultaneously with other recommended vaccines, and projected increases in coverage after elimination of missed opportunities for simultaneous vaccination.

RESULTS

Varicella vaccine coverage rates increased from 26% in 1997 to 87% in 2004. State-specific coverage rates increased 44 to 80 percentage points and were >80% in 42 states and >90% in 13 states by 2004. Coverage among susceptible children increased from 62% in 1999 to 88% in 2004. From 1998 onward, no statistically significant differences in coverage were found between white and black children, whereas Hispanic children had higher coverage rates than white children in 1998 to 2001 and 2004. Risk factors for undervaccination included living in the Midwest region, living in a household with >1 child, living in nonmetropolitan areas, living below the poverty level, having a mother who did not have a college degree, and having public providers. If missed opportunities for simultaneous vaccination had been eliminated, then coverage rates would have increased from 58% to 94% in 1999 and from 87% to 96% in 2004.

CONCLUSIONS

Uptake of varicella vaccine has been steady and is an example of successful elimination of racial and ethnic disparities. Additional focus should be placed on reducing missed opportunities for simultaneous vaccination, improving coverage in rural areas and the Midwest region, and closing remaining gaps related to maternal education, provider type, and multiple-children households.

Fulminating varicella despite prophylactic immune globulin and intravenous acyclovir in a renal transplant recipient: should renal patients be vaccinated against VZV before transplantation?

We describe a case of fulminating varicella despite prophylactic immune globulin and intravenous acyclovir in a renal transplant recipient. This promoted a survey of all 383 adult patients awaiting a renal transplant in Scotland, which showed a low level of Varicella zoster virus (VZV) awareness but a willingness to consider vaccination if non immune. 359/363 serum samples tested were seropositive for VZV antibody giving a susceptibility to VZV of 1.2%. Although data on vaccination in adults with chronic kidney disease are limited, expert opinion is of the view that the benefits of vaccinating immunocompetent seronegative patients before transplantation are likely to outweigh the risks. We believe that adult patients awaiting a transplant in the UK should be tested for their susceptibility to VZV and that early vaccination should be offered to those who are both immunocompetent and seronegative.

Do the benefits of varicella vaccination outweigh the long-term risks? A decision-analytic model for policymakers and pediatricians

Although varicella vaccine is recommended for infants, many physicians and parents have withheld vaccination from infants because of concerns about the vaccine's long-term efficacy. We used a decision-analytic Markov model to examine the effects of decreasing vaccine efficacy on individuals and society. The model incorporated published data on age-specific incidence, morbidity, and mortality rates, as well as data on shifting disease burden from childhood to adulthood as vaccine compliance increases. The effects of 2 vaccination strategies---vaccinating infants at age 12 months and waiting to vaccinate until children are 10 years of age---were compared with the effects of no vaccination. If the efficacy of the vaccine were to decrease by 75%, then 50% compliance with vaccination at age 12 months would save 1800 life-years and 12,800 quality-adjusted life-years annually in the United States. The quality-adjusted life expectancy of individuals vaccinated at age 12 months would be 63 h longer than that of nonvaccinated individuals and would increase to 79 h as vaccination compliance increases and the burden of chickenpox shifts to adulthood. Varicella vaccination of infants at age 12 months appears to be beneficial, even if the efficacy of the vaccine declines substantially.

Immunisation against varicella in end stage and pre-end stage renal failure. Trans-Pennine Paediatric Nephrology Study Group

OBJECTIVES

To investigate the seroconversion rate and duration of persistence of protective antibody titres after varicella immunisation in children with renal failure.

DESIGN

32 children (25 end stage and 7 pre-end stage renal failure) were immunised using 2 x 2,000 plaque forming unit doses of varicella vaccine 3 months apart. Varicella antibody titres were measured by enzyme linked immunosorbent assay.

RESULTS

All children initially seroconverted after immunisation. At a mean follow up of 20.3 months, 23 of 28 had protective antibody titres, 4 children having died of unrelated causes. Two children required a third booster dose. 11 children underwent renal transplantation; 10 had protective titres at the time of transplantation and, at a mean of 23.4 months after immunisation, 6 currently have protective titres. Minor side effects occurred after 11 vaccine doses in 9 children. No child developed varicella, despite 10 clear episodes of exposure to the wild-type virus.

CONCLUSIONS

Varicella immunisation in children with end stage and pre-end stage renal failure results in a high rate of seroconversion and persistence of protective antibody titres. More widespread use of the vaccine before renal transplantation is recommended.