dr. fahad razak was pulling into a toronto vaccine centre last weekend when a woman, clearly frustrated about something, gestured for him to roll down his window. “they don’t have pfizer,” the exasperated woman said. “they only have moderna.”razak was puzzled by his encounter with the perfect stranger. “i’m surprised, and intrigued and curious about why there has been such a popular imagination, a fixation, on pfizer as being superior to moderna, when there is no evidence that i, or any scientist that i work with — and we’ve looked extensively — can find to support even the smallest claim that one is better than the other.”while health authorities are reassuring canadians that it’s safe to mix covid-19 vaccines doses, and that doing so may even produce a more robust immune response, some appear to be rejecting moderna for pfizer.ontario pharmacies are reporting cancellations, walkouts, no-shows and lack of interest for moderna, after ontario and other provinces scaled up moderna doses this week because of stalled pfizer shipments. not every pharmacy is struggling, but “we know that there is supply sitting still in pharmacies for moderna,” justin bates, ceo of the ontario pharmacists association said wednesday.ontario has now received this week’s delayed pfizer doses, and allocations are being sent to public health units, but with more pfizer shipments expected to lag moderna in coming weeks, bates and others are calling for stronger public health messaging to clear up confusion about vaccine “interchangeability,” preferred brands and whether there is any downside to getting a second dose sooner than expected.razak, an internal medicine specialist at st. michael’s hospital in toronto, is hopeful that only a small minority of the public views pfizer as superior to moderna. “there may be some brand recognition and recall happening,” he said. “i don’t know if that has influenced people’s perception.” his wife received astrazeneca for her first dose, and, this past weekend, moderna for her second. “i certainly would not be saying this publicly and doing something different for my family,” razak said.the no-shows and walkaways for moderna don’t appear to be having a wide impact, infectious diseases physician dr. isaac bogoch, a member of the province’s covid-19 vaccine distribution task force, tweeted tuesday. more than 207,800 covid shots were administered in ontario on tuesday alone; most (88 per cent) were second doses.but the brand shopping has health authorities across the country concerned about any reluctance to swap. the formulas may not be identical, but they are “extremely similar and it’s perfectly okay to get one dose of each,” dr. deena hinshaw, alberta’s chief medical officer of health, said in a series of tweets monday. “we will do our best to make sure that we have both products available at our clinics, but sometimes that simply isn’t possible,” dr. bonnie henry, british columbia’s provincial health officer said.it’s also crucial that anyone considering only one dose of any vaccine knows that one dose doesn’t quite cut it.early results from a canadian study based on nearly 6,000 dried blood spot samples collected from feb. 8 to may 17 show a “high degree of variability” in the level of antibodies produced by just a single shot of a covid vaccine.approximately 10 per cent of people who reported being vaccinated with a single dose of an mrna vaccine (pfizer-biontech or moderna), and 30 per cent of those vaccinated with oxford-astrazeneca did not show signs of antibody levels “above thresholds differentiating them from the population at large,” meaning the unvaccinated, dr. philip awadala, national scientific director of canpath, which led the study, said in a statement.a single dose of pfizer or moderna produced short-term antibody levels more than one-and-a-half times greater than those produced by astrazeneca. antibody levels in people with two doses of pfizer or moderna were almost twice as high as those after the first dose.the early results don’t include people who received two doses of astrazeneca.