Lai Jianyu, Sobhani Hamed, Coleman Kristen K, Tai S-H Sheldon, Hong Filbert, Sierra Maldonado Isabel, Esparza Yi, McPhaul Kathleen M, Zhu Shengwei, DeVoe Don L, Ortiz Justin R, Chen Shuo, Yellin Temima, Carreno Juan Manuel, Krammer Florian, Cowling Benjamin J, Gordon Aubree, Chen Wilbur H, Srebric Jelena, Milton Donald K
medRxiv. 2025 May 1:2025.04.28.25326458. doi: 10.1101/2025.04.28.25326458.
The relative importance of influenza transmission via inhalation (airborne), direct deposition (spray), and contact (touch) remains poorly understood. We implemented a controlled human influenza virus infection transmission trial to study transmission pathways.
We established a quarantine hotel with individual rooms for participants and recruited healthy Recipients for two-week cohort stays. We recruited Donors with community-acquired influenza virus infection, confirmed by qRT-PCR. Donors and Recipients interacted in a room with limited ventilation and controlled humidity. We collected ambient and personal bioaerosol, Donor exhaled breath, and fomite surface swab samples. We analyzed aerosol and surface swab samples using dPCR and florescent focus assays, and sera by hemagglutination inhibition (HAI) assay and enzyme-linked immunosorbent assay.
We enrolled four Recipient cohorts (one Feb 2023 and three Jan-Feb 2024) and recruited Donors for two 2024 cohorts. We exposed 11 Recipients (mean age: 36; 55% female) to 5 Donors (mean age: 21; 80% female; two H1N1, three H3N2) for 82 Donor-hours. Among 16 breath samples from Donors, 7 G-II fine (<5µm), one G-II coarse (≥5µm), and 2 of 24 NIOSH ambient air (one ≥4µm and one 1-4µm) tested PCR positive. We cultured influenza virus from 1 G-II fine aerosol and 1 of 23 surface swab samples. No Recipient developed influenza-like illness or PCR-positive swabs or saliva. Admission sera for 8 of 11 Recipients had HAI titers ≤10, and 9 of 11 had stronger binding antibody responses than respective Donors, against vaccine strains corresponding to Donor viruses.
We successfully recruited community-acquired influenza Donors and exposed healthy Recipients under controlled conditions. However, the unpredictable timing of influenza seasons, a small eligible Recipient pool, pre-existing immunity, and limited virus shedding by Donors posed significant challenges. Addressing these factors will be critical for optimizing future study designs and improving our understanding of influenza transmission dynamics.
We designed a controlled intervention trial to identify whether influenza virus spreads between people mainly by breathing contaminated air (airborne/inhalation transmission), spray (direct deposition) of large semi-ballistic droplets at close range, or touch (contact). Understanding how influenza spreads can help improve strategies for prevention, vaccine development, and public health policies. We recruited four cohorts of healthy volunteer Recipients to stay in a quarantine hotel for two weeks. We asked them to interact in a poorly ventilated room with Donors who had recently become infected with influenza virus during their normal activities. We successfully recruited a total of five Donors to interact with 11 Recipients over the course of two quarantine cohorts. We detected small quantities influenza virus in Donor exhaled breath, in room air, and on surfaces, and none of the Recipients became infected. Unpredictability of the influenza season, a small pool of eligible Recipients, Recipient immunity, and Donors more than 24-hour post symptom onset with low rates of shedding presented significant challenges. These results suggest that new designs capable of bringing together larger numbers of Donors, early in the course of infection, with susceptible Recipients will be required to increase the odds of observing transmission.
流感通过吸入（空气传播）、直接沉积（飞沫传播）和接触（触摸）传播的相对重要性仍未得到充分理解。我们开展了一项受控的人类流感病毒感染传播试验，以研究传播途径。
我们设立了一家隔离酒店，为参与者提供单人房间，并招募健康的接受者进行为期两周的队列研究。我们招募经定量逆转录聚合酶链反应（qRT-PCR）确诊为社区获得性流感病毒感染的捐赠者。捐赠者和接受者在通风有限且湿度可控的房间内互动。我们收集了环境和个人生物气溶胶、捐赠者呼出的气体以及物体表面拭子样本。我们使用数字聚合酶链反应（dPCR）和荧光焦点测定法分析气溶胶和表面拭子样本，并通过血凝抑制（HAI）试验和酶联免疫吸附测定法分析血清。
我们纳入了四个接受者队列（一个于2023年2月，三个于2024年1月至2月），并为2024年的两个队列招募了捐赠者。我们让11名接受者（平均年龄：36岁；55%为女性）接触5名捐赠者（平均年龄：21岁；80%为女性；两名H1N1，三名H3N2），共接触82个捐赠者小时。在来自捐赠者的16份呼气样本中，7份G-II细颗粒（<5微米）、1份G-II粗颗粒（≥5微米）以及24份美国国家职业安全与健康研究所（NIOSH）环境空气样本中的2份（一份≥4微米，一份1 - 4微米）经PCR检测呈阳性。我们从1份G-II细颗粒气溶胶和23份表面拭子样本中的1份培养出了流感病毒。没有接受者出现流感样疾病，或拭子或唾液PCR检测呈阳性。11名接受者中有8人的入院血清血凝抑制效价≤10，11名接受者中有9人针对与捐赠者病毒对应的疫苗株产生了比各自捐赠者更强的结合抗体反应。
我们成功招募了社区获得性流感捐赠者，并在受控条件下让健康的接受者接触。然而，流感季节时间不可预测、符合条件的接受者群体较小、预先存在的免疫力以及捐赠者病毒脱落有限等因素带来了重大挑战。解决这些因素对于优化未来研究设计和增进我们对流感传播动态的理解至关重要。
我们设计了一项受控干预试验，以确定流感病毒在人与人之间传播主要是通过呼吸受污染的空气（空气传播/吸入传播）、近距离喷洒大的半弹道飞沫（直接沉积）还是触摸。了解流感的传播方式有助于改进预防策略、疫苗研发和公共卫生政策。我们招募了四个队列的健康志愿者接受者，让他们在隔离酒店住两周。我们让他们在通风不良的房间里与在正常活动中最近感染流感病毒的捐赠者互动。在两个隔离队列期间，我们成功招募了总共5名捐赠者与11名接受者互动。我们在捐赠者呼出的气体、室内空气和物体表面检测到少量流感病毒，但没有接受者被感染。流感季节的不可预测性、符合条件的接受者群体较小、接受者的免疫力以及症状出现后超过24小时且病毒脱落率低的捐赠者带来了重大挑战。这些结果表明，需要新的设计，以便在感染过程早期将更多的捐赠者与易感接受者聚集在一起，以增加观察到传播的几率。
