[ Sign up for our Health IQ newsletter for the latest coronavirus updates ]Labels of the Pfizer-BioNTech and Moderna vaccines call for a three or four-week gap between doses.Research has shown one dose is 70 to 80 per cent effective for up to two months, but it’s unclear how long protection lasts beyond that.Saskatchewan Premier Scott Moe said Thursday his province is moving to the four-month interval because the federal government has done a “disappointing job at best” in quickly getting vaccines to provinces.Manitoba Premier Brian Pallister added: “Let’s face it: this strategy has become necessary as a consequence of an absence of vaccines.”A Health Canada official said Thursday that a decision on Johnson and Johnson’s COVID-19 vaccine.