In France, four coronavirus disease 2019 (COVID-19) vaccines, developed by Pfizer/BioNTech, Moderna, AstraZeneca, and Janssen-Cilag, have received emergency use authorization (EUA) and a rapid vaccination program had commenced to protect its citizens from the infection. The COVID-19 pandemic has been caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) which has been characterized as highly transmissible, virulent, and has a high mortality rate.
In January 2021, elderly people and frontline workers, who were at a high risk of COVID-19 infection, were prioritized for SARS-CoV-2 vaccination. However, gradually, it was extended to younger age groups down to 12 years of age. Although the vaccination coverage rapidly increased, it slackened significantly by the end of the summer.
The need for booster COVID-19 vaccines
The emergence of SARS-CoV-2 variants occurred due to mutations. Scientists have categorized the variants as variants of concern (VOC) and variants of interest (VOI). In February 2021, SARS-CoV-2 Alpha VOC became dominant in metropolitan France, which was replaced by Delta VOC. At present, the Delta variant has become the dominant circulating strain and has been characterized as more virulent and transmissible than the original SARS-CoV-2 strain.
It can also evade the immune response induced by vaccines or natural infection. Many studies have reported that the efficacy of the available COVID-19 vaccines has been lower in the case of the Delta strain compared to other SARS-CoV-2 variants. Previous studies have also shown waning of immune protection, elicited via vaccines or natural infection, with time.
 vaccines, developed by Pfizer/BioNTech, Moderna, AstraZeneca, and Janssen-Cilag){kind=link}