EPIDEMIOLOGIC EFFECTS OF VARICELLA VACCINATION

In China, varicella is the third most frequently reported vaccine-preventable infectious disease after tuberculosis and influenza, and imposes a heavy burden on families and society. To inform future immunization policy, we investigated disease burden of varicella in China and explored cost-effectiveness of different varicella vaccination strategies at national and provincial levels.

A dynamic transmission model was developed to assess disease burden of varicella and the impact of varicella vaccination in China. A cost-effectiveness analysis of three alternative vaccination strategies in China's National Immunization Program (NIP) compared with no vaccination was conducted. Scenario analyses and sensitivity analyses were performed to check the robustness of the results.

It was estimated that 3.35 million new varicella cases occurred in 2019, more than three times of 982 thousand cases officially reported from National Notifiable Infectious Disease Surveillance System (NNIDSS). The under-reported rate was approximately 71%. The economic analysis revealed that from the societal perspective, the incremental cost-effectiveness ratio (ICER) for one dose of varicella vaccination in NIP was US$ 2357 per QALY at the national level and it was cost-effective in 22 of 31 provinces. The ICER for one dose varicella vaccination plus a mass catch-up for unvaccinated children aged 2–11 years old would be US$ −5260 per QALY, cost-saving at the national level. The one dose plus mass catch-up NIP strategy was also cost-saving in 24 of the 31 provinces.

Varicella incident cases were substantially under-reported in China. Varicella vaccination in the NIP could significantly contribute to reducing the burden of varicella disease. From the societal perspective, including varicella vaccination into China's NIP was highly cost-effective at the national level and in most provinces.

Bill & Melinda Gates Foundation.

The classic nonlinear Kermack–McKendrick model based upon a system of differential equations has been widely applied to model the rise and fall of global pandemic and also seasonal epidemic by introducing a forced harmonic infectivity which would change throughout the year. These methods work well in their respective domains of applicability, and for certain diseases, but they fail when both seasonality and high infectivity are combined. In this paper we consider a Susceptible–Infected–Recovered, or SIR, model with two latent states to model the propagation and evolutionary history of varicella in humans. We show that infectivity can be calculated from real data and we find a nonstandard seasonal variation that cannot be fitted with a single harmonic. Moreover, we show that infectivity for the present strains of the virus has raised following a sigmoid function in a period of several centuries. This could allow the design of vaccination strategies and the study of the epidemiology of varicella and herpes zoster.

An economic evaluation of universal varicella vaccination in Italy was performed to assess the potential clinical and economic effects of three different strategies versus no vaccination. By means of the EVITA model, vaccination with two doses in toddlers only (1–1.5 years), adolescents only (13 years) and toddlers with adolescents catch-up programmes were simulated. All universal varicella vaccination strategies including toddlers (with or without an adolescent catch-up programme) turned out to be highly effective in reducing the burden of disease due to varicella. In addition, they lead to significant net savings from the societal perspective but to higher costs compared to return of investment from National Health Service perspective. The huge economic burden of hospitalised uncomplicated varicella cases registered in Italy can partially explain these highly beneficial findings for the societal perspective. Overall, our analysis confirmed the favourable clinical and economic impact of routine varicella vaccination with two doses of vaccine in Italy.