As the coronavirus assumes contagious new forms around the world, two drug makers reported on Monday that their vaccines, while still effective, offer less protection against one variant and began revising plans to turn back an evolving pathogen that has killed more than two million people.

The news from Moderna and Pfizer-BioNTech underscored a realization by scientists that the virus is changing more quickly than once thought, and may well continue to develop in ways that help it elude the vaccines being deployed worldwide.

With coronavirus infections rising and a contagious new variant threatening to accelerate the pandemic, France has implemented a stringent 6 p.m.-to-6 a.m. curfew. Citizens nationwide are sequestered indoors, and businesses must close down.

In Quebec, Canadian officials imposed a similar restriction earlier this month, running from 8 p.m. to 5 a.m. It has frayed nerves: Notably, a woman who was walking her boyfriend on a leash at 9 p.m. has argued that this was permitted during the curfew, surely one of the pandemic’s most unexpected moments.

WASHINGTON — The Centers for Disease Control and Prevention has quietly changed its recommendations for coronavirus immunizations to give doctors the flexibility to handle “exceptional circumstances,” a spokeswoman said, even though the changes have not been studied in large clinical trials.