Got a source? I don't remember anyone objecting to studying HEPA filters' impact on airborne viruses. In fact, I've found studies on that exact topic from that time period. The CDC was saying that HEPA combined with masks was more effective than masking alone back in 2021 (but masking alone was better than HEPA alone)

> Without the HEPA air cleaners, universal masking reduced the combined mean aerosol concentration by 72%. The combination of the two HEPA air cleaners and universal masking reduced overall exposure by up to 90%. The HEPA air cleaners were most effective when they were close to the aerosol source

  2022: https://pubmed.ncbi.nlm.nih.gov/35947419/
  2022: https://pubmed.ncbi.nlm.nih.gov/34098798/
  2021: https://www.cdc.gov/mmwr/volumes/70/wr/mm7027e1.htm

Things changed alot, in 2020 the message was different because they were forced to admit they were wrong.