Due to shortages of N95 respirators, the FDA approved the use of KN95 and other alternative respirators. However, officials have discovered that counterfeit respirators have flooded the marketplace. Additionally, some respirators that were pulled for random testing failed to meet performance standards.
You should always confirm the authenticity of any respirator against the list of respirators approved by the FDA and NIOSH. You should also verify their performance through fit-testing.
The authenticity of a respirator can be verified by checking the FDA’s emergency use authorization list (this document is being updated regularly with respirators that meet the FDA’s eligibility criteria): https://www.fda.gov/media/136663/download