Unpopular opinion but if you're interested in the effects of a medical product, it's 'RCT or bust' for me.
I can see the case for observational analyses when randomization isn't possible, ethical, or the condition is too rare or some other such thing, but there's no such excuse here.
Saloni@scientificdiscovery.devWorth noting that many (not all) of the observational studies so far have been funded by GSK, which sells the shingles vaccine.
Vaccines are great and the shingles vaccine is also great (for shingles), but people have got to be a little more skeptical of observational studies funded by pharma IMHO.