首先各种疫苗的clinical trial 的 primary endpoint assessment,从来都不是通过测试所有参与trial人群筛查核酸阳性率得到疫苗的有效率， 而是计算存在症状+核酸阳性的感染人数。被公认的50%有效率标准也是基于这个计算率。
covid疫苗的设计和有效率计算遵从公认的疫苗大规模人群实验的原理，没有问题。
这个可以引入已经开展很久的流感疫苗trial 常规做法和有效率 （efficacy) 的定义和计算方法。被接受的 positive case definition
A Study to Evaluate the Efficacy of GSK Biologicals' Influenza Vaccine in Children
https://www.clinicaltrials.gov/ct2/show/NCT01218308
To confirm influenza A and/or B disease, （条件1）a positive reverse transcriptase polymerase chain reaction (RT-PCR) result for influenza A or B virus from a nose and throat swab obtained concurrently with an influenza like illness (ILI) （条件2）was required. ILI was defined as the presence of an oral or axillary temperature ≥ 37.8 degrees Celsius (°C) in the presence of at least one of the following symptoms on the same day: cough, sore throat, runny nose or nasal congestion.
