COVID-19 Vaccinated Individuals Can Be a Source of SARS-CoV-2 Transmission—A Systematic Review

Abstract

Fundamental rights are probably given back earlier to COVID-19 vaccinated individuals assuming that they cannot spread SARS-CoV-2 anymore. The objective of the study was to determine if COVID-19 vaccinated individuals can still be the source of SARS-CoV-2 transmission. PubMed was searched for studies on 4 April 2021. All studies with original data on COVID-19 cases among vaccinated individuals (phase III RCTs) and on viral load in the upper respiratory tract of vaccinated macaques after a SARS-CoV-2 challenge were included. Symptomatic COVID-19 cases were found in four trials among vaccinated participants although less frequently than among control subjects. One study revealed asymptomatic COVID-19 cases in a similar frequency among 2.168 AZD1222-vaccinated subjects (1.0%) compared to 2.223 control subjects (1.0%). In 15 studies with vaccinated macaques, it was found that the load of SARS-CoV-2 RNA, subgenomic RNA and infectious virus in the upper respiratory tract is variable. Sterilizing immunity was found in none of the animal studies. Major limitations of the animal studies are that the SARS-CoV-2 challenge took place within a few weeks of the final or only vaccine dose, that the viral challenge was often high and, in some studies, administered by up to four routes. Based on current knowledge it seems clear that COVID-19 vaccinated individuals can still be the source of SARS-CoV-2 transmission.