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Dr. Alan Bernstein is president and chief executive officer of the global research organization CIFAR. Dr. André Veillette is a professor at the Université de Montréal and the director of the Molecular Oncology Research Unit at the Montreal Clinical Research Institute. Prof. Bartha Knoppers is Canada Research Chair in Law and Medicine and director of the Centre of Genomics at McGill University. They are all members of Canada’s COVID-19 Vaccine Task Force.

In less than a year, the world’s scientific community has developed two mRNA vaccines against SARS CoV-2, the virus responsible for the global pandemic crisis. Within weeks, we can expect the results of Phase 3 trials of two viral vector vaccines. Science has more than delivered on its role in defeating this virus.

But producing and distributing sufficient supply for everyone on the planet to receive two doses of the mRNA vaccines as quickly as possible is proving to be as, or more, challenging than the science itself. Here in Canada, we have had two significant growing pains: delivery of the vaccines by our federal government, and the vaccination program rollout by provinces and territories.

The current, likely temporary, shortage of supply has prompted calls for altering the two-dose schedule for the mRNA vaccines by either delaying the second dose until more supply is delivered, omitting the second dose altogether or decreasing the amount of vaccine administered by 50 per cent. Strong ethical arguments can be made to vaccinate as many people as possible straight away, rather than leaving second doses in the freezer for the approved three or four weeks.

But there are also strong ethical, political and scientific reasons why that would be a serious mistake.

First, vaccines based on RNA technology have never been tried on humans before. We should not, therefore, lightly tamper with approved protocols that are based on rigorous experimentation.

Second, the protocol that Health Canada approved for the Pfizer and Moderna vaccines, based on clinical trials involving a two-dose regimen scheduled three and four weeks apart respectively, gave 95 per cent protection. It is highly unlikely that altering the dosage schedule will improve on that result.

Third, the second booster is critical as it serves two roles: It trains our immune system by improving the quality and quantity of the antibodies that are made, and it makes them more durable. There is a real risk that a single dose or a lengthy delay between doses will not achieve the level or durability of protection seen in trials. This could lead people to assume they are immune when they are not.

Fourth, to alter the protocol without any supporting evidence or regulatory approval constitutes an experiment on human subjects and therefore requires informed consent. Ethics, like science, should be based on evidence.

Fifth, viral variants have recently emerged that appear to be more transmissible. This is not surprising. All living things mutate and are selected for by the environmental conditions in which they grow. By relaxing the dosage regimen – resulting in individuals with only low levels of neutralizing antibodies – we run the great risk of creating a perfect environment where resistant variants could flourish and compromise the effectiveness of current vaccines.

Sixth, this situation is especially worrisome in frail populations, such as the elderly, cancer patients and others with a weakened immune response. So the very population who are the most vulnerable to SARS CoV-2 are the ones most at increased risk of severe disease resulting from altered dosage.

Seventh, vaccine manufacturers may be reluctant to send further doses to countries that alter regimens that were approved by the national regulator, based on the science.

And finally, here in Canada, vaccine hesitancy is low and confidence in our country’s regulatory processes higher than in many other countries. We risk undermining this trust if provinces move away from a uniform and approved dosing regimen across the country. Our course of action must be driven by data and science, not by short-term supply and delivery issues.

That we have two, and possibly soon four, highly effective vaccines against COVID-19 is a remarkable triumph of science. We now face the daunting task of manufacturing and rolling out millions of doses, but it would be a tragedy if we solved this challenge by compromising effectiveness. Instead, we must continue to depend on human ingenuity and collaboration to rapidly immunize Canadians and people everywhere.

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