Received: 17 May 2021
Accepted: 8 July 2021
First Online: 22 July 2021
Ethics approval and consent to participate
: Ethical approval and consent was not specifically for this study as we used summary data that is publicly available.
: JWD declares personal fees from Chiesi, Boerhinger Ingelheim, AstraZeneca and GSK. None have relevance to this paper. The other authors have no competing interests to declare.