In my country, we had 6 weeks between the doses. The main reason was shortage of vaccines, of course; nowadays the 6-week interval has been abolished and you can actually get the second dose earlier if you will, b/c "peak jab" is over and further interest wanes.

I am one of the "six week vaccinees", which sits just in the middle of the two sets studied in this paper. I wonder what the results for 6 week delay are.

Accidentally, Delta does not seem to be a problem yet in my country. IDK if it is luck, an early phase of a future wave or an effect of Pfizer doses being given 6 weeks apart, but our current Covid numbers are much more moderate than expected.