MEXICO CITY -- A surge in COVID-19 cases is hitting nearly all countries in the Americas, the head of the Pan American Health Organization (PAHO) said Wednesday, adding that the pandemic's toll in 2021 could be worse than last year if containment efforts relax.

From Canada to Argentina, coronavirus infections are spiking, with particularly alarming jumps documented across Caribbean island nations, even as the first vaccine doses are being administered, PAHO Director Carissa Etienne told reporters on a webcast news conference.

"If we remain diligent, we have the power to control this virus," she said. "If we relax, make no mistake, 2021 could well be far worse than 2020."

Etienne pointed to data from earlier this month showing an increase in infections in Costa Rica and Belize in Central America. The same data shows particularly concerning spikes in the Caribbean's Cayman and Virgin Islands, Barbados, the Grenadines, Bonaire, St. Vincent as well as her native Dominica, she said.

All countries in South America have seen a rise in infections over the past few weeks, Etienne said, even those where cases had previously been declining, like Chile and Argentina.

The summer months in the southern hemisphere will likely make limiting gatherings and travel more difficult, she added, which would could "fuel infections for weeks and months to come."