A vaccine can prevent illness from the novel coronavirus, but as real-world vaccinations take place out of clinical trial settings, there are still some unanswered questions.
“Should we expect the pandemic to be over once a vaccine is available for public use? Not exactly,” Julian Daniel Sunday Willett, a PhD student at McGill University, wrote in a recent column for Global News.
“A vaccine will not be perfect, and it takes time for the immune system to be ready to protect us.”
Here’s how it works:
A vaccine is generally made up of a weakened or a dead virus, which, once injected, prompts the body to fight off the invader and build immunity.
Instead of injecting a deactivated form of the virus, the mRNA vaccine uses a component of the virus DNA called messenger RNA that basically contains the genetic instructions for the human body to make the specific spike protein of the coronavirus.
By doing this, the immune system learns to recognize and respond to that specific protein, meaning it can more quickly mount a response if the virus enters the body. The mRNA, however, does not modify a person’s DNA or genetic makeup.
“When your body actually sees the real virus, then you have the weapons already in place — the antibodies and the cells that know this virus that can recognize it — and can kill it faster,” Dr. Donald Vinh, an infectious disease specialist and a medical microbiologist at the McGill University Health Center, told Global News.
How long will protection last?
According to the data from the clinical trials, Pfizer’s vaccine, which is 95 per cent effective, can offer partial protection as early as 12 days after the first dose.
That protection can last for at least two months, according to Vinh. A second dose is then required to achieve the vaccine’s full potential.
The data also showed that a second dose given 21 days later boosted the immune response, offering protection starting one week after the second jab.
Moderna’s candidate, which is still pending approval by Health Canada, can mount protective antibody levels within two weeks of the first dose and last for at least three months, Vinh said.
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The Moderna vaccine, which also requires a second shot, has shown to be 94 per cent effective.
However, it still remains to be seen what the long-term immune response will be after vaccination.
“We’ve only started using this particular product in humans since March when the Phase 1 clinical trials began, so we don’t actually know how long protection will last,” Dr. Isaac Bogoch, an infectious disease specialist at the University of Toronto, said during a media briefing on Zoom.
“And clearly, this is something that is going to be studied formally with time to see if perhaps people do need a booster vaccine.”
While more research is required, Dr. Supriya Sharma, Health Canada’s chief medical adviser, said in a press conference last week that there are promising early findings in this area.
“I have to say so far, from the data, it does look like that immunity is continuing. And certainly from some of the earlier animal data in the pre-clinical trials, it looks like it is conferring longer-range immunity. But that’s something that’s an ongoing question.”
Can a vaccine prevent the spread of coronavirus?
Vaccines are typically designed to prevent people from getting sick with the virus, but it is not yet clear if the COVID-19 vaccines by Pfizer or Moderna can stop you from transmitting the virus to others.
This is why is it important for people to continue taking precautions — physical distancing, wearing masks and avoiding gatherings, especially in poorly-ventilated spaces — until the vaccine is rolled out on a large enough scale so that we know its impact on both infection and transmission, Vinh said.
As experience with past vaccinations has shown, he added, the more people are immunized, the better the chances of reaching herd immunity
According to the World Health Organization (WHO), herd immunity is when a population can be protected from a certain virus, like COVID-19, if a threshold of vaccination is reached. It’s achieved by protecting people from a virus, not by exposing them to it, the WHO said.
“What we’ve seen with the rollout of the flu vaccines for the last several decades is that it also decreases transmission in the community so that even people who cannot get vaccinated… they can still be protected because other people in the community are vaccinated,” Vinh said.
When are we safe?
Experts suggest at least 70 to 75 per cent of the population will have to be immunized to control the spread of the virus.
“The effectiveness of these vaccines are only going to be as good as the number of people who get them,” Vinh said.
In the early stages, Canada, like the U.S., is focusing on high-risk groups, including long-term care workers and residents, those aged above 80, front-line health care workers, and Indigenous community members.
Dr. Anna Banerji, an infectious disease specialist at the University of Toronto, said this prioritization can help in a significant drop in the number of hospitalizations and deaths.
“What we need is for most of the people to get vaccinated so that the outbreak goes down and we get herd immunity,” she told Global News.
“You want to first vaccinate the people at highest risk of severe disease or death.”