When cases in northern Italy got to the hundreds, German news were full with the position has been that Coronavirus was like influenza with a strong seasonal component. This was because the national plan for the disease included that idea. However, since Monday March 9th, they have adjusted it. This [1] is a (german-language) statement from Monday by a scientist involved in that effort. He mentions a study from the USA, but doesn't give any details that make the paper easily findable. The only study I could find was this [1] one. It studies the same topic and has a similar conclusion, but might not be the one that the change was based on. Relevant part of the abstract:

> Here, we examine province-level variability of the basic reproductive numbers of COVID-19 across China and find that changes in weather alone (i.e., increase of temperature and humidity as spring and summer months arrive in the North Hemisphere) will not necessarily lead to declines in COVID-19 case counts without the implementation of extensive public health interventions.

[1]: https://www.youtube.com/watch?v=DyK9PSsnCI8

[2]: https://www.medrxiv.org/content/10.1101/2020.02.12.20022467v...