Epidemic modeling expert Jean-Stéphane Dhersin explains how variants with reduced vaccine susceptibility could spread more readily, especially as France builds immunity against the original SARS-CoV-2 strain and the dominant UK variant.
On April 26, 2021, French Prime Minister Jean Castex visited Roissy airport to highlight a new protocol for travelers from high-risk countries including South Africa, Argentina, Brazil, Chile, and India. He noted that South African and Brazilian variants remained rare and were declining in France.
These variants currently account for a tiny fraction of cases in France, yet they raise concerns alongside the emerging Indian variant. The original strain and UK variant dominate, with current vaccines providing effective protection. However, other variants enable immune escape—a phenomenon detailed by Jean-Stéphane Dhersin, researcher at the Analysis, Geometry, and Applications Laboratory (LAGA) at Paris 8 University, in 20 Minutes.
"The more vaccinated and immune people there are, the greater the advantage for variants that evade immunity," Dhersin warns.
Addressing whether Brazilian, South African, and Indian variants could take hold in France, Dhersin emphasizes the virus's constant mutations. Successful variants gain advantages like higher transmissibility, increased virulence, or prolonged infections. The UK variant, for instance, was 1.5 times more contagious than the original, with a reproduction rate (R) of 3.
Vaccination and barrier measures have since lowered R. Recent variants, however, benefit from immune escape—reduced sensitivity to immunity from prior infection or vaccines. Their R declines only with restrictions. Once vaccination goals are met, the UK variant's R will drop further, potentially allowing escape-prone variants to dominate and spark new waves. Dhersin advocates for robust genomic surveillance.
Spread risk rises with high incidence rates, but viral vector vaccines like AstraZeneca and Janssen lower incidence and mitigate escape risks. Success hinges on vaccine selection, public adherence to measures, and timely policy adjustments.
