Dr. Ross McKinney, Chief Scientific Officer of the American Association of Medical Colleges recently commented on the results of a preprint in medRxiv relating to the molecular biology of the Delta variant of SARS-COV-2. The study conducted in China evaluated 167 subjects infected during the period May 21 through June 18, 2021. 

It was determined that the incubation period for Delta variant was four days compared to six days for the original SARS-COV-2 strain responsible for the epidemic wave in China during early 2020.  The level of viral replication as determined PCR assay was 1,260 times greater than the original 2020 strain.

The upsurge of COVID in U.S. states with low vaccination rates in now predominately due to the Delta strain.  This virus has the ability to infect more people within a shorter time period and those infected release a high number of virus particles contributing to a more than twofold rate of infectivity.