Why COVID-19 vaccines won't return our lives to normal overnight

Early on in the pandemic, the promise of a vaccine was the promise of an escape hatch — a simple, relatively quick end to a long year of worry and, for all too many, tragedy.

Now, a month and a half after the first vaccine was approved, it's clear the vaccination stage of this pandemic isn't so much a door leading back to normal life as it is a frustratingly long road with gridlock and blind turns.

Ottawa, like the rest of Canada, is dealing with a shortage of the Pfizer-BioNTech vaccine due to production delays in Europe. The situation, which may last weeks, means retirement home residents have to wait longer for their first shot, and some long-term care home employees and residents have to delay their second doses.

As soon as you get your vaccine, you can't throw caution to the wind.- Raywat Deonandan, epidemiologist

In Ontario, it appears the general population will have to wait until August before they can get vaccinated.  

Dr. Robert Cushman, medical officer of health for the Renfrew County and District Health Unit, predicts it will take the better part of 2021 before we come close to herd immunity, a situation where enough of the population either has natural immunity, or has been vaccinated to prevent a disease from spreading.

Cushman, who successfully shepherded Ottawa through Ontario's SARS outbreak in 2003 as the city's medical officer of health, expects to see aspects of the current lockdown end well before we reach herd immunity, but expects such practices as wearing masks and limiting gatherings to persist until enough of us have been inoculated to achieve herd immunity. 

"I would say the vaccine is the defence against the virus, whereas the public health measures — what the public does, what you and I do in our everyday life — that's the offence, and that's what really keeps it at bay," he said.

After herd immunity is achieved, those offensive measures can be scrapped, but when that will happen is anyone's guess. 

"Herd immunity is not absolute. It's very relative," Cushman said. 

Forecasting herd immunity

Raywat Deonandan, an epidemiologist and associate professor with the faculty of health science at the University of Ottawa, said figuring out what percentage of the population requires the vaccine to achieve herd immunity is neither easy nor straightforward with a new virus. 

"Nobody has any idea," Deonandan said. "But it seems reasonable that somewhere between 30 and 50 per cent is when you start to see something happening in terms of measurable outcomes like hospitalization rates [declining]. But all that could go out the window if a new variant arrives with more transmissibility, or if people start doffing the mitigation measures."

While Ontario may see positive "herd effects" from inoculating those who tend to have the worst outcomes first, Deonandan said it's virtually impossible to know exactly when the moment will come where the population reaches full herd immunity. Signs that vaccines are tamping down on community spread may start when as little as 40 per cent of the population is vaccinated, or as much as 85 per cent. With measles, a highly contagious infectious disease, 95 per of the population must be immunized to achieve herd immunity. 

"You've got to keep the lid on it until herd immunity is near," Donandan said. "That means as soon as you get your vaccine, you can't throw caution to the wind."

There are several factors that make it difficult to predict herd immunity for COVID-19, including the fact we still don't know whether vaccines prevent transmission, and if they do, by how much. Other possible factors include how many people develop some natural immunity through previous infections, how well the public is abiding by physical distancing measures, and what kind of delays people face getting doses of the vaccine.

'A normal Christmas'

Like Cushman, Deonandan believes that while some of the more severe lockdown measures, such as closing businesses, will fall away well before we achieve herd immunity, other key measures including masking and gathering limits will be around for a long time to come. 

Even while the most vulnerable are protected, Deonandan points out the vaccines themselves are imperfect, leaving at least five per cent of those inoculated susceptible, and it's still not known what long-term effects COVID-19 may have on young, healthy people who typically show only mild symptoms. 

"I don't think it's appropriate to be haphazardly exposing people to this unless we're sure about these things, especially when we have another option," he said. 

Deonandan predicts the core physical distancing measures will remain well into the fall, but he thinks we can expect to hold at least some family gatherings by December.

"I fully expect us to be out of this by Christmas, in the sense that we're going to be having something resembling a normal Christmas," he said.