Photo: The Canadian Press

Sen. Lindsey Graham, R-S.C., shows his face mask as he speaks about the United States-Mexico border during a news conference at the Capitol in Washington, Friday, July 30, 2021. Graham says he is infected with COVID-19 but because he is fully vaccinated, he is mainly suffering from what feels like a mild sinus infection. THE CANADIAN PRESS/AP-Manuel Balce Ceneta

U.S. Republican Sen. Lindsey Graham says he is infected with COVID-19 but because he is fully vaccinated, he is mainly suffering from what feels like a mild sinus infection.

For public health experts, Graham's Monday tweet underscores why COVID-19 vaccines are so critical.

Dr. Zain Chagla, an infectious disease specialist at St. Joseph's Healthcare Hamilton, says breakthrough infections are still an exception in fully vaccinated people but when they do happen, the symptoms are usually very mild and short-lived.

The U.S. Centers for Disease Control last week warned the Delta variant of the virus is so contagious, vaccinated people who do get infected could be just as big a risk to others as people who aren't vaccinated.

Chagla says there is still very limited data on the contagiousness of COVID-19 among vaccinated individuals, with some signs the infectious period is at the very least much shorter.

But he says the vaccines are working so well overall that with 80 per cent of eligible Canadians now at least partly protected, he does not foresee a return to wide-scale lockdowns even as the Delta-driven fourth wave begins to rise in Canada.