Thread by @BillHanage

It is categorically impossible to know exactly when an effective vaccine will be available in advance. Anyone who says otherwise is pulling the wool over your eyes 1/n

sure you can have a pretty good idea of when enough data will have been collected to get a read on how effective the vaccine is, but you don't know in advance what the data are going to tell you 2/n

It might be good news, it might be bad, it might be mixed (eg good in some age groups, others not so much). Unless there has been a dreadful breakdown in all the things we do to make trials secure and reliable, you won't know until the data are analyzed 3/n

Among those things that ensure reliability is thoroughly investigating adverse events. Doing this is a Good Thing. We need to ensure vaccines are safe. However it will delay things such that again, it's not predictable exactly when results will be available 4/n

So if someone confidently tells you they know when a trial will report results, you know they are either not telling the truth, don't understand how vaccine trials work, don't *care* how vaccine trials work or whether the resulting vaccine is safe, or maybe all of the above 5/end