While it’s clear vaccines led to a drop in fatalities during the most recent delta variant-driven waves compared with earlier bouts with the virus, some countries saw deaths fall to a greater degree than others, an outcome scientists still don’t have answers for.

Countries like Germany, Denmark and the U.K. have seen Covid deaths fall to roughly a tenth of previous peaks, according to Bloomberg calculations using data compiled by Johns Hopkins University. In Israel, Greece and the U.S., fatalities fell but remained more than half of the previous peaks…

One thing is clear: it’s not just the type of shots nor the extent of vaccination that counts in bringing down the death toll…

Some of the places seeing lower death rates spaced their two shots further apart than the three-to-four week interval commonly used around the world. Controversial at the time, the U.K.’s decision in December to allow as long as 12 weeks between doses of the vaccine developed by AstraZeneca and the University of Oxford so more people could get their first shot is now been validated by scientific studies as providing stronger protection.