It has been shown that Mv 1 Lu cells can support low level replication of SARS-CoV, which could result in the inadvertent growth of SARS-CoV-2. Therefore, CDC recommends that laboratories discontinue the use of the A549/Mv 1 Lu mix (R-Mix ) or any other mixture containing Mv 1 Lu cell lines. Based on recent publications, (Severe Acute Respiratory Syndrome Coronavirus 2 from Patient with Coronavirus Disease, United States), A549 and MDCK cells lines (which make up R-Mix Too ) do not support SARS-CoV-2 replication. As a result, R-Mix Too may be considered for use as an alternative for R-Mix. For additional information, see SARS-associated Coronavirus Replication in Cell Lines Severe Acute Respiratory Syndrome Coronavirus 2 from Patient with Coronavirus Disease, United States