What will it take for Vancouver Island to achieve herd immunity?

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Just nine months after COVID-19 was detected in Canada, the country began its largest ever immunization program in an ambitious effort to stop widespread transmission of the virus by fall 2021.

Public health officials in British Columbia heaved a collective sigh of relief in the latter half of December as the province began administering not one, but two vaccines—supplied by Pfizer-BioNTech and Moderna—across all health authorities.

At a press briefing on Dec. 4, Provincial Health Officer Dr. Bonnie Henry said everyone who wants a COVID-19 vaccine in BC should be able to get one by September of 2021 if all goes according to plan.

This promise is contingent upon Health Canada approving several other vaccines from manufacturers like AstraZeneca and Johnson & Johnson in the spring, and a regular supply of these vaccines arriving in BC.

At the moment, the province—and the country—are in the early stages of their rollout plans. BC’s plan mostly tells us who is first in line to be immunized: staff, residents, and visitors at long-term care facilities, front-line health-care workers, and isolated First Nations communities.

Less clear are details surrounding how many people will be vaccinated each day across all health authorities, the rate at which immunization needs to occur in order to achieve community or “herd” immunity against COVID-19 by next fall, and whether we are currently on track to reach that goal.

The road so far in BC and on Vancouver Island

BC got its first doses of the Pfizer-BioNTech vaccine during the week of Dec. 14. As of Dec. 31, the province had received about 30,000 doses—17,510 of which have been administered.

For the first week, the Pfizer vaccine was only administered at two locations in the Vancouver Coastal and Fraser Health regions because, due to the vaccine’s storage and shipping challenges, it could only be administered at the point of delivery. Delivery points were set up across all health authorities starting Dec. 22.

“We have done a lot of immunizations over the last week and one of the things that we are learning is that this vaccine is fussy,” Dr. Henry said at a Dec. 29 press briefing.

“It is not a simple thing to use the Pfizer vaccine and so a lot of time over [the holiday] weekend was to build up the training… and to take the Pfizer vaccine out of the point of arrival.”

Data released by the Ministry of Health shows that, between Dec. 16 and Dec. 31, the Pfizer vaccine has been delivered at a widely varying rate, averaging about 1,094 doses per day across BC and reaching its highest point on Dec. 31 when nearly 3,500 doses were administered.

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Earlier this week, Dr. Henry and Health Minister Adrian Dix said the province expects to receive 30,000 doses of this vaccine by the end of December and plans to have administered all of these doses by next week, Jan. 4.

To get to that point, public health officials will need to immunize nearly 16,000 people in just five days, at an average rate of 3,200 vaccine doses delivered per day—a feat Dr. Henry says will take a “Herculean effort” to accomplish.

This effort may be sped up by the fact that the first doses of the Moderna vaccine have arrived in BC, totalling 1,100 as of Dec. 31. These doses—easier to transport and store than the Pfizer version—will be delivered to 10 First Nations communities identified as ‘“high risk.” The Ministry of Health has not reported how many doses have arrived in the province so far.

In the Vancouver Island Health region, public health staff started receiving the Pfizer vaccine on Dec. 21, drawing from the 1,950 doses that have so far arrived on the Island.

Both vaccines currently require a second dose, meaning any time we hear the word “doses” the actual number of people vaccinated by those doses will likely work out to about half that number in the long run, provided that dosage requirements don’t change.

According to the latest available data breakdown sent to Capital Daily by an Island Health spokesperson, 1,285 doses were administered by Dec. 28. These first doses are being provided to long-term care staff in the Greater Victoria area.

In an update on Dec. 31, minister Dix added that all 1,950 doses of the Pfizer vaccine sent to Island Health have been administered. Vancouver Island will be the only region where no immunization clinics will be held on Jan. 1, 2021.

The average daily rate of immunization on the Island so far is 214 doses administered per day. Immunization clinics across the province were closed on Dec. 25.

“Clinics were closed on Christmas Day to give health-care staff a much-needed, albeit short, break over the holidays,” a Ministry of Health spokesperson said in an emailed statement to Capital Daily.

The current rate of immunization across the province may cause BC to fall short of reaching its short-term target of administering 30,000 doses of the vaccine by next week—but the approval of the Moderna vaccine and the pending approval of the AstraZeneca vaccine in Canada, possibly within the next few weeks, mean more doses will soon be available here in BC.

What remains to be seen is how closely more supply will line up with faster immunization, and what any lag in administering the vaccine will mean for the ability to meet the goal of herd immunity by September.

What we know and don’t know

On Dec. 23, the provincial health ministry offered an update on their vaccine rollout plan.

While we still don’t know exactly how many more doses BC will receive in the first few months of 2021, the ministry’s presentation said public health officials are preparing to receive approximately 792,000 doses—representing vaccinations for a little under 400,000 people—of the Pfizer and Moderna vaccines between December and March.

Authorities plan to administer these doses to 150,000 people by February and to 400,000 more people by the end of March. This roughly corresponds to a vaccination rate of 5,188 doses per day.

“Given what we know about the virus, we’re looking at 60 to 70% of the population being immune to prevent transmission widely in the community,” said Dr. Henry in response to Capital Daily’s question regarding how many people need to be vaccinated to achieve herd immunity.

That number could increase depending on how the new UK variant (or any subsequent variants) of the virus act as they make their way into the population, Dr. Henry explained. At this point, it remains unclear just how much more infectious the new variant of the virus will be.

Existing projections of herd immunity were “based on the transmission rates we were seeing of the virus prior to the new variant we’re seeing from the UK,” Dr. Henry said. “The more infectious and transmissible a virus is, the higher the population immunity you need to have to achieve that point of being able to stop transmission.”

Given the knowledge of how much of the population needs to be vaccinated to stop widespread transmission and which groups will be the first to be immunized, some simple math can provide a sense of the daily rate of vaccination needed to reach herd immunity by fall.

“At an aggregate level, what we want to look at is, when do we expect everybody to get vaccinated? And that’s going to depend on at least two big things,” said Mahesh Nagarajan, a professor at the University of British Columbia with expertise on vaccine supply chains, distribution and mathematical modelling.

“First is the availability of the vaccine. Second is our ability to actually hand the vaccines out to people: the rate at which we want to get vaccinated.”

“I know that kids under 15 are likely not going to get vaccinated [by fall]… so we can work backwards and do the math,” he added, removing what is considered the lowest-risk group from the equation.

Statistics Canada reports show that the total population of BC is just above five million. As of 2016, children under age 15 accounted for 14.8% of the population.

Assuming that percentage holds true today, there are currently about 4.26 million people over the age of 15 residing in B.C.

If the goal is to vaccinate 70% of that population by September, there would need to be 11,469 doses administered each day. As we’ve seen with the planned vaccine rollout numbers shared by the province, the expected rate of immunization in the first few months of 2021 stands at a little over 5,000 per day, which itself is five times the rate so far.

At the rate the province expects in its plan, widespread transmission of COVID-19 will not be stopped until August 2022, a year later than the province says it’s aiming for.

Similar methods tell us the rate of immunization that will be needed on Vancouver Island. StatsCan data shows there are around 691,300 people above the age of 15 living on the Island. To vaccinate 70% of them by September, there would need to be 2,658 immunizations per day.

The current rate of immunization in the Island Health region is 214 doses per day. It remains unknown when the next shipment of Pfizer vaccines will arrive, and how many Moderna doses are now available on the Island.

These estimated rates of vaccine delivery only account for the first doses of each vaccine being given out. Once we take into account the fact that much of the new supply chain of the Pfizer and Moderna vaccines will be used to administer second doses to British Columbians starting in February, the effective rate of delivery drops even lower.

According to Minister Dix, the province will be providing a weekly breakdown of the number of vaccines delivered per health authority starting Jan. 4.

But as we’ve seen with the current gap between how many doses of the Pfizer vaccine are available and how many have actually been administered so far, supply levels are not the only factor determining the speed at which the province can roll out its immunization plan.

Challenges with remote communities

Nagarajan says the rate of immunization in the new year will largely depend on how the vaccines are delivered.

One option is for health authorities to set up sites like drive-in clinics or tents for the public to access the vaccines, along with administering them at places like hospitals and long-term care facilities.

A second model is for vaccines to be distributed at pharmacies like London Drugs and Shoppers Drug Mart, and also at clinics where people can set up appointments to get immunized.

“Think about a flu shot,” he said. “You can get a flu shot pretty much anywhere, which makes it a lot easier to administer compared to, let’s say, all of us having to go to a couple of specific locations only to get shots. That could cause lots of bottlenecks.”

Another major challenge that remains, even assuming that a steady supply of vaccines is available, is distribution to isolated communities. The Pfizer vaccine needs to be kept at -70 C.

“The vaccine needs to go in the refrigerator into residential care homes, in different communities. And that’s a major, major challenge,” said Nagarajan.

“My expectation is that many of these challenges will be reconciled in urban centres... places with high density. It's going to be a bigger challenge when we get to the more remote communities.”

One way to increase the rate of immunization that researchers are looking at is by reducing the Moderna vaccine regimen requirement from two doses to one. Doing so would free up more doses to deliver to more people.

Earlier this week, Dr. Henry said she is waiting for guidance from Health Canada and the National Advisory Committee on Immunization on whether this tactic will be considered in the long run.

“Both of these vaccines [Pfizer and Moderna] have very high effectiveness within two weeks of the first dose: upwards of 80% [immunity]... [but] we don’t know how long that immunity lasts,” said Henry.

“Right now, however, it is a two-dose program and we made the decision… that for December and January, all of our doses of both Pfizer and Moderna will be going to protect people with their first dose, because we can do that and protect almost twice as many people as if we started giving the second dose in the short time frame that is in the product monograph.”

The minimum recommended period for people to receive the second dose of each vaccine is between 21 and 28 days, but Henry says there is no outside limit to when it can be administered.

Based on the current expectations of how many vaccines are slated to arrive in BC in the next few weeks, the second doses of the Pfizer vaccine will start to be administered in February.

As the new year approaches, bringing with it the beginning of the end of the COVID-19 pandemic, there is still much we don’t know for sure about when we can finally put physical distancing measures in the rearview mirror.

But Nagarajan says he has faith in the provincial government to keep us updated on the vaccine rollout program whenever more information is available to them.

“One thing we know is this: if they know, they will tell us.”