Studies conducted in Israel where more than 25 percent of the population has been immunized using the Pfizer mRNA vaccine showed benefits both with respect to individual protection and reducing transmission rates.  An analysis was performed on the cycle threshold of positive PCR tests in a large public health laboratory before and after initiation of intensive vaccination of individuals older than 60 years.  By early February, 75 percent of this cohort had received their first dose 14 days previously and 25 percent of the cohort between the age of 40 and 60 had also received their first dose 14 days previously. There was no difference in the PCR cycle threshold between the two age groups in mid-January. 

During the last two weeks of January there was a significant reduction in the cycle threshold values in the older group.  Applying a nested linear model to PCR data it was possible to determine that viral load was decreased two-fold in individuals positive for SARS-CoV-2.  It is anticipated that this difference will become more obvious after the second dose administered to a larger proportion of the older group.  The investigation indicated that vaccination not only provides protection but can also reduce transmission rates in the community.

Better, E. et al Initial real world evidence for lower viral load of individuals who have been vaccinated with BNT- 162b2. Med R xiv. doi.org/10.1101/2021.02.08.21251329 February 2021.