It might be a lower risk to innoculate in the the glute then getting a primary infection in the lung first. We do not know yet and that's what vaccine trials are for. We know that the spike protein is probably the target though. That protein and fragments can be amplified and expressed and tested as vaccines.
Your search for a live attenuated strain would probably take 18 months minimum and probably longer. You need widespread testing and sequencing which are both in short supply. You also need outcome data. You would also need a sufficient sample size and then hope that your predicted attentuated cohort is say not just all young people.
No it won’t take long. We already have the samples (they are what has been sent in to labs) and with modern genomic tools you could sequence 100,000 samples for under a million dollars in a couple of weeks at most.
The mutation rate is just an average - anyway we are looking for one specific mutation and in the 6 months SARS-CoV-2 has been around there has been plenty of time for the right mutant strain to have arisen.
It doesn’t matter who the cohort is - all that matters is the strain has the right mutation.
Your search for a live attenuated strain would probably take 18 months minimum and probably longer. You need widespread testing and sequencing which are both in short supply. You also need outcome data. You would also need a sufficient sample size and then hope that your predicted attentuated cohort is say not just all young people.
Sars-Cov2 mutation rate is <26bp per year. https://nextstrain.org/ncov/global?l=clock