The explanation: With vaccination rates rising in both countries, Canadian and U.S. lawmakers, business leaders, and families separated from loved ones for more than a year have been urging Trudeau and President Joe Biden to start easing restrictions.

Trudeau said the decision to keep the frontier sealed for another month to foreign travelers, including Americans, was largely due to the government’s concerns that fully vaccinated individuals may still be able to transmit Covid-19. He said Canada had yet to reach a high enough threshold of second-dose vaccination.

“Even a fully vaccinated individual can pass on Covid-19 to someone who is not vaccinated,” Trudeau said, referring to the guidance driving Canada’s “phased” reopening approach.

Trudeau reiterated the need for Canada to reach its vaccination targets before it can start peeling back restrictions. He wants at least 75 percent of the population to have had their first Covid vaccine doses and 20 percent to be fully vaccinated.

The frustration: The decision drew swift disapproval from those demanding a reopening.

“There’s no other way to say it: another month’s delay is bullshit,” Rep. Brian Higgins (D-N.Y.), co-chair of the Congressional Northern Border Caucus, wrote on Twitter later Friday.

Higgins and Bill Huizenga (R-Mich.), two of the most-vocal lawmakers pushing for the border measures to be eased back, issued a joint statement later Friday condemning the two governments’ approach to an issue that they say affects millions of people on both sides.

“The lack of transparency surrounding these negotiations is a disservice to our constituents and the millions of residents on both sides of the border waiting to see their loved ones, visit their property, and renew business ties,” said the message from Higgins and Huizenga, who both serve as co-chairs of the Canada-United States Inter-Parliamentary Group. “While the arrival of vaccines in record time has been a modern marvel, the inability of the U.S. and Canadian governments to reach an agreement on alleviating border restrictions or aligning additional essential traveler classes is simply unacceptable.”

Goldy Hyder, president of the Business Council of Canada, said Friday that the two countries missed an opportunity to make adjustments to the border agreement to recognize the growing number of people who are fully vaccinated against the virus.

“Canadians need a clearly articulated plan to reopen the border safely so that friends and families can be reunited and businesses can welcome back travelers,” Hyder said in a statement.

The border agreement: Canada-U.S. land crossings have been closed to nonessential travel since March 2020, when the public health measures were imposed to help prevent Covid-19’s spread.

The countries have renewed a month-to-month agreement to keep the restrictions in place — and the latest one had been set to expire Monday.

Last week, Canada signaled it would start easing quarantine requirements during the first week of July for returning Canadians, permanent residents and other people who are permitted to enter the country. Public Safety Minister Bill Blair said Friday on Twitter that more details on the changes will be announced Monday.

Part of the backstory: The delays have fed concerns that decision-makers are being guided more by politics than science.

Provincial premiers like Ontario’s Doug Ford have urged the Trudeau government to keep tough border measures in place, while recent public opinion polls have suggested many Canadians want the border restrictions to stick around until the end of summer.

What’s next: Trudeau said Friday that in the coming weeks, Canadians returning to the country will be able to upload their proof of vaccination records to an app managed by the federal government.

The prime minister said that for the fall, Ottawa and the provinces are also working on a national certification of vaccination status that will be accepted by countries around the world.