Studies about COVID transmission via wind instruments show that some instruments pose higher risks (e.g., trumpets) than others. Risk-reduction measures include (1) distancing and/or rearranging players; (2) wearing face masks designed especially for wind and brass players; and (3) using bell covers. 

Links to articles about covid transmission:  
nontechnical: https://www.sciencenews.org/article/coronavirus-covid-music-wind-instruments-spread-transmissionhttps://www.sciencenews.org/article/coronavirus-covid-music-wind-instruments-spread-transmission  
technical: Journal of Aerosol Science 151 (2021) 105669 
ongoing research: https://www.nfhs.org/articles/unprecedented-international-coalition-led-by-performing-arts-organizations-to-commission-covid-19-study/. 

Bell Covers and Instrument Masks 
Bell covers help contain the spread of aerosols. Bell covers with a multi-layering material and filtration should be used. MERV 13 filters can be cut to fit and be inserted in the back opening of the bell cover to provide enhanced protection as recommended by the U. Colorado aerosol study. MERV 13 material is readily available at most home improvement stores. 

Bell covers: 
https://sepapparel.com/bell-cover.html 
https://www.amazon.com/s?k=bell+covers+for+instruments&i=mi&crid=3CM8HTTR2VHMT&ref=nb_sb_ss_ts-doa-p_2_10 

Some instrument masks for wind players: 
https://sepapparel.com/instrument-mask.html 
https://www.amazon.com/s?k=instrument+mask+for+wind+players&ref=nb_sb_noss_2