One of Canada's top public health officials sought to reassure Canadians today that a recommendation from a federal vaccine advisory committee to stretch out the time between COVID-19 vaccine doses is a sound one. Yesterday, the National Advisory Committee on Immunization (NACI) recommended that the maximum interval between the first and second doses of all three COVID-19 vaccines approved for use in Canada should increase to four months due to limited supplies. Deputy Chief Public Health Officer Dr. Howard Njoo said the advice is based on real-world data that shows doing so would lead to more people being protected from COVID-19 in a shorter time period. "This recommendation is based on clinical trial reports and emerging real-world evidence from around the world. Data shows that several weeks after being administered, first doses of vaccines provide highly effective protection against symptomatic disease, hospitalization and death," Njoo told a technical briefing today. Confusion over conflicting advice Njoo's comments appeared to be addressing the confusion created by the fact that NACI's recommendation conflicts with those issued by Health Canada when it granted regulatory approvals for the Pfizer-BioNTech, Moderna and AstraZeneca vaccines. Regulatory documents provided by Health Canada upon approval of each vaccine state that the second dose of the Pfizer-BioNTech should be taken three weeks after the first, the second Moderna shot should come four weeks after the first, and the second AstraZeneca dose should be delivered between four and 12 weeks after the first. All of those recommendations are in line with the product monograph provided by the manufacturers. Adding to the confusion, NACI recommended on Monday against giving the AstraZeneca-Oxford vaccine to people 65 and older, although Health Canada has authorized it for use in adults of all ages. But Njoo said the discrepancies can be explained by the fact that Health Canada is a regulator and NACI is an advisory body made up of medical experts. "You have likely noticed that NACI's recommendations are sometimes different, possibly broader or narrower than the conditions of vaccine use that Health Canada has authorized. As the regulator, Health Canada authorizes each vaccine for use in Canada according to factors based on clinical trial evidence, whereas NACI bases its guidance on the available and evolving evidence in a real-world context, including the availability of other vaccines," Njoo said. "What we expect is that NACI recommendations will complement — not mirror — those of Health Canada." WATCH: Njoo comments on NACI recommendation to delay second COVID-19 vaccine doses The issue burst into the open on Monday when B.C.'s Provincial Health Officer Dr. Bonnie Henry announced that the province would be extending the interval between doses of the Moderna, Pfizer and Oxford-AstraZeneca vaccines to 16 weeks. Some medical experts questioned that decision. Canada's chief science adviser, Mona Nemer, said doing so without proper clinical trials amounts to a "population level experiment." Dr. Anthony Fauci, the top infectious disease expert in the U.S., told the Washington Post that the science doesn't support delaying a second dose for the Pfizer-BioNTech and Moderna vaccines. He said there isn't enough evidence to determine how much protection is provided by one dose of those vaccines, and how long it lasts. Despite those warnings, several provinces followed Henry's lead and even more have indicated they intend to stretch the dosage interval. While it appeared to some at the time that Henry was moving faster than the science, Njoo said that NACI's experts briefed provincial medical officers of health over the weekend on the results of their analysis before releasing their recommendations publicly. NACI concluded that stretching the dosing interval to four months would allow up to 80 per cent of Canadians over the age of 16 to receive a single dose of COVID-19 vaccine by the end of June, without compromising vaccine effectiveness. "While studies have not yet collected four months of data on vaccine effectiveness after the first dose, the first two months of real world effectiveness are showing sustained high levels of protection," NACI said. As for the AstraZeneca-Oxford vaccine, Njoo said it is safe and that evidence shows it provides protection against very serious disease and death in people of all ages. He said Health Canada has a rigorous scientific review process and only approves vaccines that meet high standards for safety, efficacy and quality. Dr. Supriya Sharma, Health Canada's chief medical adviser, said expert advice will continue to change as more data becomes available from ongoing mass vaccination campaigns, and she urged provinces and territories to consider recommendations and evidence from both bodies when making decisions about their vaccine strategies. "The messaging would be simpler if we had one set of data and we had one message and it never changed, but that's not what science does," said Sharma. Decision on Johnson and Johnson imminent At today's briefing, health officials also indicated that a regulatory decision on whether to approve Johnson & Johnson's COVID-19 vaccine is expected soon. "The review of the Johnson & Johnson submission is going very well, it's progressing, and we're expecting to have that completed and a decision in the next few days. I would say in the next seven days or so," said Sharma. The company has said its vaccine is 66 per cent effective at preventing moderate to severe illness in a global clinical trial, and much more effective — 85 per cent — against the most serious symptoms. Canada has agreed to purchase up to 38 million doses if it is approved. The U.S. Food and Drug Administration approved it for use in that country last Saturday. The approval of a fourth vaccine would give a significant boost to Canada's vaccine rollout. Johnson and Johnson's vaccine is widely seen as one of the easiest to administer because it requires only one dose and can be stored for long periods of time at regular refrigerator temperatures. Njoo said additional vaccines, coupled with the NACI recommendation on dosage intervals, could allow Canada to meet the goal of inoculating all adults who want a vaccine "several weeks" before the current target date of the end of September. Maj.-Gen. Dany Fortin, the military commander leading Canada's COVID-19 vaccine logistics, said that while more vaccines would be good news, the current target remains the end of September.