Ask the Pharmacist

Q) I hear some countries, and provinces, advocating that we should delay giving people the booster dose of a COVID vaccine in order to get more people vaccinated with at least their initial dose. Other countries and the manufacturers of the vaccines seem to be against this idea. What is the right response?

A) This is a question that most countries (although not all – England expects to have all of their most vulnerable people protected by mid February, an accomplishment that makes Canada’s efforts look weak in comparison) are grappling with given the scarcity of vaccine supply and the challenges in administering the vaccines that we do have in a timely fashion.

Some provinces, including Ontario, are essentially out of vaccine supply and we have in the last few weeks been told that further supplies will be delayed (including no fresh supply this week at all) as Pfizer, one of the two manufacturers of approved vaccines in Canada thus far, needs to “retool” its European manufacturing plant.

We know the scientific trials with the two vaccines prove that they work in the 95% range when two doses are given between three to four weeks apart. We do not know, for sure, what their efficacy will be when the doses are separated to a larger extent. Some countries such as Denmark and Britain have already approved delaying booster doses and Germany is considering this. Quebec has just, somewhat astonishingly approved a 90 day delay.

To put this in perspective, England’s approved delay is 12 weeks (84 days). Ontario just approved up to a 42 day interval in between receiving the two doses. So, just what is the right answer? Well, before we debate the relative merits of both sides of the equation, one needs to define just what is the actual answer we are looking for. The best solution to vaccine scarcity is the one that will save the most lives. That is the bottom line. Both sides of this quandary have compelling arguments in favour of them.

The argument for staying with the manufacturers’ recommendations centres mostly on science, which is never a bad place to base your opinion on. They include the fact that these two vaccines are the very first we have ever developed that make use of RNA technology. Given our relative inexperience with vaccines of this nature, we should be hesitant to alter the protocols that have been developed through rigorous testing. We also know that when the two doses are given at the specified intervals, they are 95% protective against a virus that looks like it’s here with us to stay. It is extremely unlikely that changing this interval will improve upon these numbers.

Thirdly, there have been reports that the manufacturers are not pleased with these proposed delays and may make countries that enact them pay by further limiting their supply in favour of countries that are following the original protocols.

As well, we have seen the development of variants of the COVID vaccine such as the U.K., Brazillian and South African ones (and possibly a new one in California that is being investigated at the time of this writing). There is a possibility that in relaxing our dosage scheduling, we will have individuals with only low levels of circulating antibodies, in particular those with weakened immune systems such as the elderly or those with immune compromising diseases such as cancer, after one dose. This may result in creating a near perfect environment for the virus to mutate even faster.

It is important to note that, despite the fact that there are a number of variants, which are created by mutations in the genetic code of the virus, COVID is actually a relatively slow virus to do this. This is indeed a blessing. If COVID mutated as quickly as the flu virus does, we would likely be in far more dire straits than we currently are, possibly morphing into a version that does not respond to the vaccines or is more lethal.

It appears as though the variants that have been discovered thus far are more contagious but not more deadly and are also susceptible to the current vaccines. This is a real possibility as witnessed by the fact that patient zero for the U.K. variant is believed to have been an immuno-compromised person who had a rare chronic disease.

Lastly, this second dose of the vaccine is crucial. It serves two purposes. It essentially further trains our immune system to improve both the quality and the quantity of the antibodies needed to fight off the virus particles. It also makes these antibodies more durable. There is a risk therefore, that a lengthy delay may not achieve the same level of protection or durability seen in the trials leading to our being under protected when we eventually mingle back in public spaces once again.

On the flip side, there are very compelling reasons to delay the second dose. The first one is obvious. We will be able to vaccinate far more of our most vulnerable in a timely fashion and we know that even a single dose of the two vaccines confers a significant level of protection. Most experts estimate that one shot should provide immunity in the 60 to 85 % range, although there is wide variability in the studies with the numbers ranging from just above 50% all the way up to 90%. Even at the lower end, that is still a massive boost to our ability to fight off this virus should we be infected by it. And time is critical.

The U.K. variant, which we should start calling by its proper name, B.1.1.7, doubles the number of people it infects every 10 days as opposed to the 40 days of the original version of the virus. It has spread so quickly in England that it is estimated that 1 in 30 people in London have the virus. This new variant is here in Ontario and recent modelling has predicted that it will be the dominant form of the disease in our province by the end of February. Predictions as of January 10th for Ontario suggested this could lead to 6,000 cases daily by the end of the month and 800 in our I.C.U.’s which would overwhelm our hospital capacity.

Given this, should we really leave millions of doses of vaccines waiting in fridges/freezers across the province for weeks when we could be saving lives right now when we need to most?

As well, the basis for the three to four week protocol was not selected because of scientific evidence that the vaccines would work better when given this many weeks apart. That interval was chosen based on the need to develop and test vaccines as quickly as possible. We know they work with the shorter interval but there is no evidence that stretching that interval longer will affect the efficacy.

The majority of vaccines administered in Canada are given at least a month and frequently two months apart and there is evidence that a number of them work better and for a longer period of time when the interval is kept closer to its maximum. There is also evidence that the protection from the first dose lasts for many weeks. The Vaccine Committee that heads the U.K.’s response has estimated that a single dose of one of the vaccines will prevent 70% of serious cases for at least 9-12 weeks. This will give us time to acquire millions of more doses and start giving people their booster shot.

Getting back to the question; Just what the correct answer is, no one’s really sure but more and more countries seem to be choosing the same path as Ontario in delaying the second dose. There is excellent news that vaccinating people will get much easier in the very near future. According to the New York Times vaccine tracker, there are 30 more vaccines in the final phase of testing, including one from Johnson & Johnson that requires only a single injection and is stable in a normal fridge which should make the widespread distribution of this vaccine far less complicated. For more information about this or any other health related questions, contact your pharmacist.