One last thing: the title of this thread is a falsehood based on the classic logical fallacy of equating absence of evidence to evidence of absence. Let’s look at the facts:
- Because this is an emergency situation (a rapidly spreading global pandemic with a substantial death rate) time is of the essence. Therefore, it is perfectly sensible for the initial clinical trials of vaccines to focus on the most important and fastest-to-answer questions: is it safe? and does it reduce the rate of symptomatic disease?
- It’s true that the phase III trial doesn’t explicitly test for a reduction in infection. That would require near-daily PCR swab testing of every single trial participant - a big ask for tens of thousands of unpaid volunteers (particularly given the discomfort of the nasal swab) for what is actually very little new information.
- We already know from the phase I and II trials that the vaccines (a) are safe, and (b) stimulate the production of “neutralising” antibodies (that is, antibodies that bind to the virus in the right way to block it’s ability to enter a cell).
So, put two and two together: neutralising antibodies (known from phase I/II) and a massive reduction in symptomatic infections (from phase III). The obvious conclusion is that it’s overwhelmingly likely that the vaccines are doing exactly as expected and blocking infection completely. But, even if all they was reduce the symptoms to nothing without actually preventing infection, that’d still be valuable - since it’s the symptoms that actually kill.
