首先各種疫苗的clinical trial 的 primary endpoint assessment,從來都不是通過測試所有參與trial人群篩查核酸陽性率得到疫苗的有效率， 而是計算存在症狀+核酸陽性的感染人數。被公認的50%有效率標準也是基於這個計算率。
covid疫苗的設計和有效率計算遵從公認的疫苗大規模人群實驗的原理，沒有問題。
這個可以引入已經開展很久的流感疫苗trial 常規做法和有效率 （efficacy) 的定義和計算方法。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, （條件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) （條件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.
