A new study is offering data to back one of the core assumptions about the spread of Covid-19: The intensity of exposure to the virus matters, and vaccines and prior infections can only help so much – but they do indeed help.

The research, led by scientists at the Yale School of Public Health and published in the Nature Communications journal, also reinforces the common-sense notion that masks and air filtration can augment the protection provided by a vaccine and lower the risk of getting the virus. Anyone watching Covid-19 cases bubble back up in their community should take that to heart: Infections are not unavoidable, and the tools we have been using to protect ourselves are not just intuitive – and certainly should not be controversial. They are increasingly backed up by evidence.