Only a marginal reduction in efficacy has been noted the elderly (>60-65 years) in the trials conducted to date. With regards to comorbidities, current trials have shown no difference in efficacy compared to persons without comorbidities. Theoretically they may be less effective in persons with decreased immune system, however the limited trials to date have not shown this.
There is currently no data on how long the vaccines will provide protection against re-infection.
END.