Funding for this research was provided by:
Received: 18 September 2020
Accepted: 20 January 2021
First Online: 2 February 2021
: RKM is a PhD candidate at Goethe University, Frankfurt. He is a full-time employee of a multinational chemical company involved in vitamin D business and holds the shares of the company. This study is intended to contribute to the ongoing COVID-19 crisis and is not sponsored by his company. The other authors declare no competing interests. The views expressed in the paper are those of the authors and do not represent that of any organization. No other relationships or activities that could appear to have influenced the submitted work.