The Danish paper on negative effectiveness can be because Denmark required proof of vaccination to attend large events. If some of those events were superspreader events you would see an apparent negative effectiveness.
Same sort of result out of Canada, which also required vaccination for large events:
The Danish paper on negative effectiveness can be because Denmark required proof of vaccination to attend large events. If some of those events were superspreader events you would see an apparent negative effectiveness.
Same sort of result out of Canada, which also required vaccination for large events:
https://www.medrxiv.org/content/10.1101/2021.12.30.21268565v1