Department of Epidemiology, University of Michigan, 48109, Ann Arbor, MI, USA.
Department of Mathematics, University of Michigan, 48109, Ann Arbor, MI, USA.
BMC Med. 2022 Oct 8;20(1):387. doi: 10.1186/s12916-022-02534-7.
Varicella zoster virus (VZV) is one of the eight known human herpesviruses. Initial VZV infection results in chickenpox, while viral reactivation following a period of latency manifests as shingles. Separate vaccines exist to protect against both initial infection and subsequent reactivation. Controversy regarding chickenpox vaccination is contentious with most countries not including the vaccine in their childhood immunization schedule due to the hypothesized negative impact on immune-boosting, where VZV reactivation is suppressed through exogenous boosting of VZV antibodies from exposure to natural chickenpox infections.
Population-level chickenpox and shingles notifications from Thailand, a country that does not vaccinate against either disease, were previously fitted with mathematical models to estimate rates of VZV transmission and reactivation. Here, multiple chickenpox and shingles vaccination scenarios were simulated and compared to a model lacking any vaccination to analyze the long-term impacts of VZV vaccination.
As expected, simulations suggested that an introduction of the chickenpox vaccine, at any coverage level, would reduce chickenpox incidence. However, chickenpox vaccine coverage levels above 35% would increase shingles incidence under realistic estimates of shingles coverage with the current length of protective immunity from the vaccine. A trade-off between chickenpox and shingles vaccination coverage was discovered, where mid-level chickenpox coverage levels were identified as the optimal target to minimize total zoster burden. Only in scenarios where shingles vaccine provided lifelong immunity or coverage exceeded current levels could large reductions in both chickenpox and shingles be achieved.
The complicated nature of VZV makes it impossible to select a single vaccination scenario as universal policy. Strategies focused on reducing both chickenpox and shingles incidence, but prioritizing the latter should maximize efforts towards shingles vaccination, while slowly incorporating chickenpox vaccination. Alternatively, countries may wish to minimize VZV complications of both chickenpox and shingles, which would lead to maximizing vaccine coverage levels across both diseases. Balancing the consequences of vaccination to overall health impacts, including understanding the impact of an altered mean age of infection for both chickenpox and shingles, would need to be considered prior to any vaccine introduction.
水痘带状疱疹病毒（VZV）是已知的八种人类疱疹病毒之一。初次 VZV 感染会导致水痘，而潜伏一段时间后的病毒再激活则表现为带状疱疹。目前已有单独的疫苗用于预防初次感染和后续再激活。由于水痘疫苗接种可能会对免疫增强产生负面影响的假设，即通过接触自然水痘感染来增强 VZV 抗体，从而抑制 VZV 的再激活，因此大多数国家并未将其纳入儿童免疫接种计划，从而引发了关于水痘疫苗接种的争议。
此前，利用来自泰国的水痘和带状疱疹人群发病通知数据，应用数学模型对 VZV 传播和再激活率进行了估算，泰国既不接种水痘疫苗也不接种带状疱疹疫苗。在此，模拟了多种水痘和带状疱疹疫苗接种场景，并与缺乏任何疫苗接种的模型进行了比较，以分析 VZV 疫苗接种的长期影响。
正如预期的那样，模拟结果表明，无论接种率如何，引入水痘疫苗都将降低水痘发病率。然而，在当前疫苗提供的保护免疫力长度下，考虑到带状疱疹疫苗接种的现实覆盖率估计，水痘疫苗覆盖率超过 35%可能会增加带状疱疹的发病率。在水痘和带状疱疹疫苗接种覆盖率之间存在权衡，发现中等水平的水痘疫苗覆盖率是作为最小化总带状疱疹负担的最佳目标。只有在带状疱疹疫苗提供终身免疫或覆盖率超过当前水平的情况下，才可能大幅降低水痘和带状疱疹的发病率。
VZV 的复杂性使得不可能选择一种通用的疫苗接种方案。侧重于降低水痘和带状疱疹发病率的策略，但优先考虑后者，应该会最大限度地提高带状疱疹疫苗接种的效果，同时逐步纳入水痘疫苗接种。或者，各国可能希望最大限度地减少水痘和带状疱疹的 VZV 并发症，这将导致在两种疾病中都最大化疫苗覆盖率。在引入任何疫苗之前，需要权衡疫苗接种对整体健康影响的后果，包括了解水痘和带状疱疹感染平均年龄改变的影响。
