I'd like to see the study first, how can we know that this year's flu variant wasn't just less infectious ? What was the sample size ? What's the p-value ?
Flu variants infectionness variability is just a so well known variable that the researchers would have to be really mediocre to not take that into account, the official press release mentions they're performing the studies on four kindergartens, so they're most probably comparing against each other.
