Oddly enough I think an Inverse Law of Vulnerability should apply: Vaccinate all the healthy 20 – 40 year- old people first and see how things are after 4 weeks. If no significant problems, roll it out to healthy children and wait another 4 weeks. If still no significant problems, vaccinate the elderly and the vulnerable.
Reasoning is two-fold – The first two groups are 1) those best able to recover from any adverse affects; 2) those most likely transmitters of the infection because they have to have to interact at school or in the workplace (and during social interaction, because most of them seem incapable of a) NOT going down the pub/shopping/going on Protest Marches against xxxxx (insert your cause here), or b) Social Distancing properly. Or, indeed, at all. Ever.