While in most instances, Type 2 is caused by diet, however it is also genetics as well. There are people that are normal weight and who are in good shape that do not eat poorly and are still diabetic. Moreover, once a diabetic, always a diabetic. There is no cure. You can control blood sugar levels with a plant based high fiber diet. But it’s not a cure. Insulin resistance continues.
As far as the CoVid vaccine, I have refuted your claim on many different occasions. the polio vaccine was not studied for decades before being administered. That is a fallacy. The human trials began in 1954. The trials revealed that the vaccine had an 80-90% efficacy rate. In 1955, it was approved to be distributed. Polio at its height only killed 56,000 people in a year. Dr Salk developed his vaccine in 1953 and tried it on his family. The next year in 1954 it was human trials, then early 1955, the vaccine was being distributed. The vaccine was not studied for decades before being distributed by the American public.
I would think 70 year later science would be able to improve the speed upon whether vaccines are able to be used. The CoVid vaccine while certainly not having an 80-90% efficacy rate like the polio vaccine, was extraordinarily safe. Of the 10's of millions of doses given, how many deaths are directly attributable to the vaccine? Zero? if there are any the percentage is .0000000001%.