小规模的临床一期，证实mRNA 流感疫苗是安全的，并可以产生抗流感抗体，但水平较低，主要的缺陷是抗体消退比较快，故预计提供保护的时间短，这一点与新冠疫苗很像。另外该实验（临床1期）主要是检测疫苗的安全性，而非实际的抗流感感染的效果。
参见：
1. mRNA vaccines against H10N8 and H7N9 influenza viruses of pandemic potential are immunogenic and well tolerated in healthy adults in phase 1 randomized clinical trials, https://www.sciencedirect.com/science/article/pii/S0264410X19305626?via%3Dihub
2. mRNA flu shots move into trials, https://www.nature.com/articles/d41573-021-00176-7
部分段落的机器翻译：
迄今为止，关于基于 mRNA 的流感疫苗报告的唯一人体数据来自 Moderna 首次进入临床。从 2015 年底开始，该公司评估了两种两剂疫苗，每种疫苗都针对不同的禽流感病毒株设计。
根据前 Moderna 首席营销官 Tal Zaks 的说法，这些试验的主要目标是对公司的 mRNA 进行试运行。 “如果你想证明这项技术是有效的，最简单的起点就是流感疫苗，”他说。他解释说，对于流感，保护的相关性——可以预测疫苗功效的免疫参数测量——是明确定义的。也有成熟的疫苗可以参考临床结果。
对于许多旁观者来说，Moderna 的第一次试验令人失望。尽管大多数接受较高剂量实验性疫苗的研究参与者产生的流感特异性抗体滴度高于被认为具有保护作用的阈值（通过经过充分验证的血凝抑制 (HAI) 测定法测量），但这些抗体水平在免疫接种后的几个月内逐渐下降.这表明这些提供的保护可能是短暂的。根本无法检测到 T 细胞免疫。
The only human data reported to date on an mRNA-based flu vaccine come from Moderna’s first foray into the clinic. Beginning in late 2015, the company evaluated a pair of two-dose vaccines, each designed against a different strain of avian influenza.
According to former Moderna CMO Tal Zaks, the main goal of those trials was to give the company’s mRNA a test run. “If you want to show that the technology works, the easiest place to start is with an influenza vaccine,” he says. With influenza, he explains, the correlates of protection — measurements of immune parameters that allow prediction of vaccine efficacy — are well defined. There are also established vaccines to reference clinical results to.
To many onlookers, Moderna’s first trials were a disappointment. Although most study participants who received higher doses of the experimental vaccines developed influenza-specific antibody titres above the threshold thought to be protective — as measured by the well-validated haemagglutination inhibition (HAI) assay — those antibody levels tapered off within just months of immunization. This suggests that the protection these offer might be short-lived. T-cell immunity was not detectable at all.
