自2020年12月以来,公共卫生机构实施了各种疫苗接种策略,以遏制SARS-CoV-2的传播,以及现有的非药物干预措施(NPI)。最初的策略侧重于为老年人接种疫苗,以防止住院和死亡,但是随着疫苗的普及,确定最佳策略以安全解除NPI,同时避免病毒死灰复燃变得很重要。
我们扩展了经典的确定性SIR隔室疾病传播模型,以模拟不同疫苗推出场景下NPI的提升。使用多伦多的病例和疫苗接种数据,加拿大在2020年12月28日至2021年5月19日期间,我们估计了NPI升级/放松的过去阶段的传播,以比较在不同日期取消NPI对病例的影响。住院治疗,和死亡,根据20岁年龄组不同程度的疫苗覆盖率,解释免疫力下降的原因。
我们发现,一旦老年人的覆盖率足够高(至少一次剂量为80%),目标的主要年龄组是20-39岁和40-59岁,其中,如果要在夏季取消NPI,则到2021年6月中旬需要至少70%的第一剂覆盖率,以最大程度地减少死灰复燃的可能性。虽然NPI取消的每一种情况都有复苏,我们还发现,在乐观的疫苗接种覆盖率下(到6月中旬70%的覆盖率,以及将2021年8月的重新开放推迟到2021年9月)可以在2021年12月31日之前将病例数和严重结果减少约57%。
我们的结果表明,将疫苗接种策略集中在工作年龄人群上可以遏制SARS-CoV-2的传播。然而,即使成年人的疫苗接种覆盖率很高,增加接触和放松个人保护性行为是不可取的,因为预计会出现复苏,尤其是早些时候重新开放。
Since December 2020, public health agencies have implemented a variety of vaccination strategies to curb the spread of SARS-CoV-2, along with pre-existing Nonpharmaceutical Interventions (NPIs). Initial strategies focused on vaccinating the elderly to prevent hospitalizations and deaths, but with vaccines becoming available to the broader population, it became important to determine the optimal strategy to enable the safe lifting of NPIs while avoiding virus resurgence.
We extended the classic deterministic SIR compartmental disease-transmission model to simulate the lifting of NPIs under different vaccine rollout scenarios. Using
case and vaccination data from Toronto, Canada between December 28, 2020, and May 19, 2021, we estimated transmission throughout past stages of NPI escalation/relaxation to compare the impact of lifting NPIs on different dates on cases, hospitalizations, and deaths, given varying degrees of vaccine coverages by 20-year age groups, accounting for waning immunity.
We found that, once coverage among the elderly is high enough (80% with at least one dose), the main age groups to target are 20-39 and 40-59 years, wherein first-dose coverage of at least 70% by mid-June 2021 is needed to minimize the possibility of resurgence if NPIs are to be lifted in the summer. While a resurgence was observed for every scenario of NPI lifting, we also found that under an optimistic vaccination coverage (70% coverage by mid-June, along with postponing reopening from August 2021 to September 2021) can reduce
case counts and severe outcomes by roughly 57% by December 31, 2021.
Our results suggest that focusing the vaccination strategy on the working-age population can curb the spread of SARS-CoV-2. However, even with high vaccination coverage in adults, increasing contacts and easing protective personal behaviours is not advisable since a resurgence is expected to occur, especially with an earlier reopening.