Vaccination des adultes contre la varicelle et le zona

The impact of 2-dose routine measles, mumps, rubella, and varicella vaccination in France on the epidemiology of varicella and zoster using a dynamic model with an empirical contact matrix

PURPOSE

Varicella has a high incidence affecting the vast majority of the population in France and can lead to severe complications. Almost every individual infected by varicella becomes susceptible to herpes zoster later in life due to reactivation of the latent virus. Zoster is characterized by pain that can be long-lasting in some cases and has no satisfactory treatment. Routine varicella vaccination can prevent varicella. The vaccination strategy of replacing both doses of measles, mumps, and rubella (MMR) with a combined MMR and varicella (MMRV) vaccine is a means of reaching high vaccination coverage for varicella immunization. The objective of this analysis was to assess the impact of routine varicella vaccination, with MMRV in place of MMR, on the incidence of varicella and zoster diseases in France and to assess the impact of exogenous boosting of zoster incidence, age shift in varicella cases, and other possible indirect effects.

METHODS

A dynamic transmission population-based model was developed using epidemiological data for France to determine the force of infection, as well as an empirically derived contact matrix to reduce assumptions underlying these key drivers of dynamic models. Scenario analyses tested assumptions regarding exogenous boosting, vaccine waning, vaccination coverage, risk of complications, and contact matrices.

FINDINGS

The model provides a good estimate of the incidence before varicella vaccination implementation in France. When routine varicella vaccination is introduced with French current coverage levels, varicella incidence is predicted to decrease by 57%, and related complications are expected to decrease by 76% over time. After vaccination, it is observed that exogenous boosting is the main driver of change in zoster incidence. When exogenous boosting is assumed, there is a temporary increase in zoster incidence before it gradually decreases, whereas without exogenous boosting, varicella vaccination leads to a gradual decrease in zoster incidence. Changing vaccine efficacy waning levels and coverage assumptions are still predicted to result in overall benefits with varicella vaccination.

IMPLICATIONS

In conclusion, the model predicted that MMRV vaccination can significantly reduce varicella incidence. With suboptimal coverage, a limited age shift of varicella cases is predicted to occur post-vaccination with MMRV. However, it does not result in an increase in the number of complications. GSK study identifier: HO-12-6924.

[Current events in vaccination]

The annual meeting of the Infectious Disease Society of America (IDSA) ; which brought together nearly 5000 participants from over 80 countries in Vancouver, Canada, October 21 to 24, 2010 ; provided a review of the influenza (H1N1) 2009 pandemic, evaluated vaccination programmes and presented new vaccines under development. With 12,500 deaths in the United States in 2009-2010, the influenza (H1N1) 2009 pandemic was actually less deadly than the seasonal flu. But it essentially hit the young, and the toll calculated in years of life lost is high. The monovalent vaccines, whether live attenuated or inactivated with or without adjuvants, were well tolerated in toddlers, children, adults and pregnant women. In order to protect infants against pertussis, family members are urged to get their booster shots. The introduction of the 13-valent Pneumococcal conjugated vaccine in the beginning of 2010 may solve - but for how long ? - the problem of serotype replacement, responsible for the re-increasing incidence of invasive Pneumococcal infections observed in countries that had introduced the 7-valent vaccine. The efficacy of a rotavirus vaccine has been confirmed, with a reduction in hospitalization in the United States and a reduction in gastroenteritis-related deaths in Mexico. In the United States, vaccination of pre-adolescents against human papillomavirus (HPV) has not resulted in any specific undesirable effects. Routine vaccination against chicken pox, recommended since 1995, has not had an impact on the evolution of the incidence of shingles. Vaccination against shingles, recommended in the United States for subjects 60 years and over, shows an effectiveness of 55 %, according to a cohort study (Kaiser Permanente, Southern California). Although some propose the development of personalized vaccines according to individual genetic characteristics, the priority remains with increasing vaccine coverage, not only in infants but also in adults and the elderly. Vaccine calendars that cover a whole lifetime should be promoted, since the vaccination of adults and seniors is a determining factor of good health at all ages.

[Burden of herpes zoster and postherpetic neuralgia: Incidence, proportion, and associated costs in the French population aged 50 or over]

BACKGROUND

Despite the perspective of vaccination against herpes zoster, there are few recent data available on the incidence of this disease, the proportion of postherpetic neuralgia cases, and associated disease management costs. This study was performed to evaluate these parameters in a representative sample of French physicians.

METHODS

It was a retrospective, declarative study conducted from the medical files of patients who presented with herpes zoster and consulted in 2005, based on a random sample of GPs, dermatologists, neurologists, and physicians in pain clinics, weighted by demographic departmental distribution of patients aged 50 years and above. The analysis was performed on cases diagnosed by physicians themselves (incident cases).

RESULTS

The annual incidence of herpes zoster was estimated at 8.99/1000 [8.34-9.64], all types of physicians pooled and at 8.67/1000 for GPs. This represents about 182,500 cases of herpes zoster in France in 2005 in patients aged 50 years and above. Incidence was slightly higher amongst women (1.3 times) and increased with age. Amongst the 777 cases of incident herpes zoster, 343 were complicated by postherpetic neuralgia one month after diagnosis. The proportion of patients presenting postherpetic neuralgia at 3 and 6 months was 32.1% and 17.6%, respectively. The annual cost of management of herpes zoster and postherpetic neuralgia was estimated at 170 [109-249] million euros, of which 61.0 million euros were covered by the national health insurance.

CONCLUSION

In this study, the incidence of herpes zoster observed in France in subjects aged 50 years and above is close to that already estimated in France and Europe. The proportion of postherpetic neuralgia is high and this painful complication may persist for several months after diagnosis of herpes zoster. To our knowledge, EPIZOD is the first study conducted in France to assess the cost of herpes zoster and of postherpetic neuralgia, the most frequent complication of this viral disease.

Herpes zoster: Burden of disease in France

This work provides estimates of HZ incidence and HZ-related hospitalization and mortality rates in France, where no immunization programme has been implemented. Herpes zoster data was obtained from the Sentinelles surveillance general practitioners (GPs) network, the PMSI Data processing centre for hospital discharges and from the French National Mortality Database (INSERM CépiDC). The yearly HZ incidence rate averaged 382 cases per 100,000 inhabitants (95% CI 364-405) and exponentially increased with age. The annual rates of hospitalizations and mortality due to HZ varied from 4.14±0.32 to 14.42±0.39 and from 0.11±0.03 to 0.29±0.04 per 100,000 inhabitants, respectively, depending on whether HZ was coded in a 'primary' or 'primary or associated' diagnosis. One or more factors of immunodepression occurred in 43.4% of hospitalized cases and in 21.6% HZ-related deaths.

[Benefit-risk assessment of vaccination strategies]

This article summarises the various stages of the risk/benefit assessment of vaccination strategies. Establishing the awaited effectiveness of a vaccination strategy supposes to have an epidemiologic description of the disease to be prevented. The effectiveness of the vaccine strategy will be thus expressed in numbers of cases, hospitalizations or deaths avoided. The effectiveness can be direct, expressed as the reduction of the incidence of the infectious disease in the vaccinated subjects compared to unvaccinated subjects. It can also be indirect, the unvaccinated persons being protected by the suspension in circulation of the pathogenic agent, consecutive to the implementation of the vaccination campaign. The risks of vaccination related to the adverse effects detected during the clinical trials preceding marketing are well quantified, but other risks can occur after marketing: e.g., serious and unexpected adverse effects detected by vaccinovigilance systems, or risk of increase in the age of cases if the vaccination coverage is insufficient. The medico-economic evaluation forms a part of the risks/benefit assessment, by positioning the vaccine strategy comparatively with other interventions for health. Epidemiologic and vaccinovigilance informations must be updated very regularly, which underlines the need for having an operational and reliable real time monitoring system to accompany the vaccination strategies. Lastly, in the context of uncertainty which often accompanies the risks/benefit assessments, it is important that an adapted communication towards the public and the doctors is planned.