2 型脊髓灰质炎疫苗衍生病毒疫情和干预措施的传播模型:尼日利亚案例研究

IF 2.7 Q3 IMMUNOLOGY Vaccine: X Pub Date : 2024-03-16 DOI:10.1016/j.jvacx.2024.100476
Yuming Sun , Pinar Keskinocak , Lauren N. Steimle , Stephanie D. Kovacs , Steven G. Wassilak
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引用次数: 0

摘要

背景尽管全球根除脊髓灰质炎行动取得了成功,但根除脊髓灰质炎病毒仍面临巨大挑战。口服脊髓灰质炎病毒疫苗(OPV)中的 Sabin 株(减毒活疫苗)病毒可在接种疫苗不足的社区中恢复为疫苗衍生脊髓灰质炎病毒(cVDPV),重新具有神经毒性和传播性,并导致麻痹疫情爆发。自 2016 年停止使用含 2 型脊髓灰质炎病毒的 OPV(OPV2)以来,在世界卫生组织的六个地理区域中,有四个区域爆发了 2 型 cVDPV(cVDPV2)疫情,使这些疫情成为重大的公共卫生威胁。我们建立了一个基于微分方程的模型来模拟 cVDPV2 在 Sabin 株病毒恢复长期流通后的传播。该模型包含了基本(常规)免疫接种和补充免疫活动(SIAs)、不同脊髓灰质炎病毒疫苗诱导的免疫力以及从 Sabin 株病毒到 cVDPV 的逆转过程。该模型的结果包括每周的 cVDPV2 麻痹病例数和 cVDPV2 传播停止的消亡日期。在尼日利亚西北部和东北部的案例研究中,我们将该模型与 2018-2021 年发病的每周 cVDPV2 病例数数据进行了拟合。然后,我们使用该模型测试了 2022-2023 年预测期内不同疫情应对方案的影响。应对方案包括无应对、计划应对(基于尼日利亚的 SIA 日历)和一组假设应对,SIA 开始的日期各不相同。计划应对方案包括两轮 SIA,几乎覆盖了尼日利亚西北部和东北部的所有地区,但一些疫苗接种不足的地区(如索科托)除外。假设的应对方案包括两轮、三轮和四轮 SIA,覆盖整个尼日利亚西北部和东北部地区。在测试的疫情应对方案中,所有 SIA 都使用了 nOPV2。我们比较了预测期内测试的疫情应对方案的结果。结果模拟的 cVDPV2 每周病例数在时空上与数据一致。预测结果表明,与不采取应对措施相比,实施计划的应对措施可使病例总数减少 79%,但并未阻止传播,尤其是在疫苗接种不足的地区。与计划应对措施相比,实施两轮覆盖所有地区的 nOPV2 SIA 的假设应对措施可进一步将疫苗接种不足地区的 cVDPV2 病例数减少 91-95%,更早地完成两轮应对措施的影响更大,但并未阻止传播。当前两轮接种于 2022 年 4 月初完成时,在 2023 年 1 月下旬再实施两轮接种,阻止了传播。如果前两轮在六周前(即 2022 年 2 月底)完成,则在 2023 年 2 月初(2022 年 11 月底)增加一轮(两轮)停止传播。在尼日利亚西北部和东北部疫苗接种不足的地区,消灭脊髓灰质炎病毒总是最后实现的。研究结果表明:(i) nOPV2 能有效减少疫情病例数;(ii) 需要在 2022 年开展更多轮疫情应对 SIA,覆盖尼日利亚西北部和东北部所有地区,以阻止 cVDPV2 的爆发;(iii) 疫苗接种不足地区的持续传播延迟了阻止疫情爆发的进程;(iv) 更快的疫情应对措施将避免更多麻痹病例,并需要更少的 SIA 来阻止疫情爆发。
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Modeling the spread of circulating vaccine-derived poliovirus type 2 outbreaks and interventions: A case study of Nigeria

Background

Despite the successes of the Global Polio Eradication Initiative, substantial challenges remain in eradicating the poliovirus. The Sabin-strain (live-attenuated) virus in oral poliovirus vaccine (OPV) can revert to circulating vaccine-derived poliovirus (cVDPV) in under-vaccinated communities, regain neurovirulence and transmissibility, and cause paralysis outbreaks. Since the cessation of type 2-containing OPV (OPV2) in 2016, there have been cVDPV type 2 (cVDPV2) outbreaks in four out of six geographical World Health Organization regions, making these outbreaks a significant public health threat. Preparing for and responding to cVDPV2 outbreaks requires an updated understanding of how different factors, such as outbreak responses with the novel type of OPV2 (nOPV2) and the existence of under-vaccinated areas, affect the disease spread.

Methods

We built a differential-equation-based model to simulate the transmission of cVDPV2 following reversion of the Sabin-strain virus in prolonged circulation. The model incorporates vaccinations by essential (routine) immunization and supplementary immunization activities (SIAs), the immunity induced by different poliovirus vaccines, and the reversion process from Sabin-strain virus to cVDPV. The model’s outcomes include weekly cVDPV2 paralytic case counts and the die-out date when cVDPV2 transmission stops. In a case study of Northwest and Northeast Nigeria, we fit the model to data on the weekly cVDPV2 case counts with onset in 2018–2021. We then used the model to test the impact of different outbreak response scenarios during a prediction period of 2022–2023. The response scenarios included no response, the planned response (based on Nigeria’s SIA calendar), and a set of hypothetical responses that vary in the dates at which SIAs started. The planned response scenario included two rounds of SIAs that covered almost all areas of Northwest and Northeast Nigeria except some under-vaccinated areas (e.g., Sokoto). The hypothetical response scenarios involved two, three, and four rounds of SIAs that covered the whole Northwest and Northeast Nigeria. All SIAs in tested outbreak response scenarios used nOPV2. We compared the outcomes of tested outbreak response scenarios in the prediction period.

Results

Modeled cVDPV2 weekly case counts aligned spatiotemporally with the data. The prediction results indicated that implementing the planned response reduced total case counts by 79% compared to no response, but did not stop the transmission, especially in under-vaccinated areas. Implementing the hypothetical response scenarios involving two rounds of nOPV2 SIAs that covered all areas further reduced cVDPV2 case counts in under-vaccinated areas by 91–95% compared to the planned response, with greater impact from completing the two rounds at an earlier time, but it did not stop the transmission. When the first two rounds were completed in early April 2022, implementing two additional rounds stopped the transmission in late January 2023. When the first two rounds were completed six weeks earlier (i.e., in late February 2022), implementing one (two) additional round stopped the transmission in early February 2023 (late November 2022). The die out was always achieved last in the under-vaccinated areas of Northwest and Northeast Nigeria.

Conclusions

A differential-equation-based model of poliovirus transmission was developed and validated in a case study of Northwest and Northeast Nigeria. The results highlighted (i) the effectiveness of nOPV2 in reducing outbreak case counts; (ii) the need for more rounds of outbreak response SIAs that covered all of Northwest and Northeast Nigeria in 2022 to stop the cVDPV2 outbreaks; (iii) that persistent transmission in under-vaccinated areas delayed the progress towards stopping outbreaks; and (iv) that a quicker outbreak response would avert more paralytic cases and require fewer SIA rounds to stop the outbreaks.

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Vaccine: X
Vaccine: X Multiple-
CiteScore
2.80
自引率
2.60%
发文量
102
审稿时长
13 weeks
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