Less than two percent of the world's poorest populations have received even a first dose of vaccine, noted Flahault, director of the University of Geneva's Institute of Global Health.
"In certain places -- eastern and central Europe, Africa, Asia, Israel, Canada, El Salvador, Belize -- cases are increasing exponentially, so we can't say the pandemic is behind us," he said.
Even in rich, well-vaccinated countries showing a downward trend, things could reverse, experts caution.
As the northern hemisphere approaches winter, people will once again gravitate toward large, indoor gatherings that boost circulation of the virus.
"We have to be careful of the situation in Europe and North America as we enter the middle of autumn," says Sofonea.
"What we know about this pandemic is that it is unpredictable," added Flahault.
"No one foresaw the appearance of the Delta variant in India last spring, even though we feared that kind of thing might happen."