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Dr. Charu Kaushic: COVID vaccine questions answered by Canadian immunology expert

Immunology expert Dr. Charu Kaushic answers some common questions about the COVID-19 vaccines available to Canadians
Dr. Charu Kaushic, immunology professor at McMaster University in Ontario and member of the national COVID-19 Immunity Task Force, shared information about the COVID-19 vaccines.

With the COVID-19 vaccination rollout underway across Canada, many people have been seeking out more information about the new vaccine and how it works to provide protection from coronavirus.

Experts from the Canadian Institutes of Health Research have been fielding questions about the COVID-19 vaccines currently approved in Canada, in an effort to stem the flow of misinformation circulating in the conversation.

Dr. Charu Kaushic, McMaster University immunologist and member of Canada’s COVID-19 Immunity Task Force, is just one expert hoping to clear up any misconceptions about the effectiveness and safety of COVID-19 vaccines, by sharing her knowledge and recommending further resources. 

Messenger RNA vaccines and how they work

Right now, Health Canada has approved vaccines from pharmaceutical companies Pfizer-BioNTech and Moderna Therapeutics for use, both of which require two doses to reach full efficacy.  

Both utilize a new immunology technology known as messenger ribonucleic acid (mRNA) vaccines, setting them apart from other vaccines used to protect against other types of viruses like the flu. 

“Other vaccines have been formulated typically with whole viruses that have been inactivated or parts of virus proteins that are in the formulations. We call them subunit vaccines,” said Kaushic. “[mRNA] vaccines include part of the genetic code of the virus that is put directly into the body, and the cells then decode that and make it into proteins on their own.”

Both Moderna and Pfizer produce their mRNA vaccines in similar ways, said Kaushic. The mRNA code is enclosed in lipid nanoparticles for delivery, which then instruct the body’s immune system to begin producing the necessary antibodies to fight the virus if infected.

What separates the two, she continued, is that the genetic codes included in the Moderna vaccine and the Pfizer vaccine are slightly different from each other.

“What that means is when the virus code is decoded, the protein looks slightly different, which means that the immune responses that will be mounted will be slightly different,” said Kaushic.

Vaccine efficacy 

Studies prior to the vaccines’ release reported the Moderna vaccine was 91 per cent effective in protecting against the COVID-19 virus beginning two weeks after immunization, while the Pfizer vaccine was 95 per cent effective beginning one week after immunization. 

These statistics were gathered through studies on healthy individuals, who received both doses of the same vaccine within the recommended time frame — 28 days for Moderna, and 21 days for Pfizer.

Because the Moderna and Pfizer vaccine differ from each other slightly, Kaushic said the current recommendation is to immunize using two doses of the same vaccine and avoid mix-and-matching, to provide the most effective protection.

“Think of it in a lock-and-key kind of manner, where if there’s a certain lock and the key is slightly different, you won’t open the lock. There is probably a good chance that the immune response [between the two vaccines] would be similar, but they’re not exactly the same,” said Kaushic.

Kaushic also noted that while it has not been common, it is possible for individuals to contract COVID-19 after their first vaccine dose, especially within the one- or two-week window following vaccination.

“The two vaccines are slightly different, but the first dose is about 50 per cent protective and that’s why you need to get a second dose to reach 95 per cent protection,” said Kaushic.

Some reports are showing that individuals who become COVID-19 positive following the first vaccine dose may experience milder symptoms of the disease.

“The thought is that, and as more data is being gathered, if you had one dose of the vaccine and you’ve become positive, you should have a very mild disease because presumably, your immune system is already activated,” said Kaushic. “[But these people] should still consult with health authorities to see when to get the second dose, because there’s nothing to say they shouldn’t get that dose.”

Kaushic also confirmed that both the Moderna and Pfizer vaccines are reporting to be effective against emerging variants of the COVID-19 virus, including those discovered in the U.K., South Africa and Brazil.

Is natural immunity enough?

Experts including Kaushic agree that the most effective form of protection against COVID-19 currently is vaccination, but studies about natural immunity are still occurring. 

Some individuals who have tested positive for COVID-19 and then recovered do show a level of immunity to the virus, said Kaushic, but it seems to vary based on the person and the virus.

“We don’t know yet if every person who has contracted COVID has long-term immunity. Some people have been seen to have antibodies for easily six months and in some people, the antibody levels start going down sooner, which means they are no longer protected,” said Kaushic. “There are some indications from studies that have been done that people who had more severe COVID might have stronger immunity, or if you had a mild infection, you may not have enough [natural immunity] or for long enough.”

Cases of re-infection have occurred, said Kaushic, suggesting that natural immunity does not universally protect against the virus and its variants. 

Immunization parameters and side effects

Health Canada is closely monitoring the safety and effectiveness of the two vaccines as they are being administered to Canadians, keeping track of all reported side effects experienced following immunization.

Kaushic noted that the potential side effects of the COVID-19 vaccine are similar to those of other vaccines, due to the nature of the vaccine platform, but are not currently a safety concern.

“These are what we call reactogenic vaccines, so there is a little bit of a reaction,” said Kaushic. 

Side effects include local pain at the injection site or a sore arm, tiredness, headache and in some cases, fever, but Kaushic said these symptoms are normal and are short-term.

“It’s really no different than a flu vaccine because some people don’t feel anything at all,” she said. “It's nothing that we don’t see with other vaccines.”

Concerns about the potential side effects on more vulnerable populations are also under review, with ongoing studies looking at the vaccine’s effectiveness and side effects on individuals not previously included in clinical trials. 

Until more data is reached, Kaushic said it's still unclear if there are any potential health concerns for pregnant women, immunocompromised individuals, or young children. 

The best approach is to consult with a health provider, she said, to determine if the risks of contracting COVID-19 outweigh the known potential side effects of the vaccine.

“I wouldn’t think the vaccine is not safe for them, but the reason why some of these groups are being excluded right now is because, typically, vaccines are tested on healthy people, to make sure they are safe,” said Kaushic. “But there has not been large-scale studies on children or pregnant women, so that is why at this moment, they are being excluded [from some vaccination plans].”

All individuals in Canada are encouraged to get vaccinated once it is available to them, said Kaushic, including individuals who have tested COVID-positive, provided they are no longer symptomatic.

For now, the only people warned to avoid vaccination are those who have had monoclonal antibodies or convalescent plasma administered, as studies are still ongoing.

It's also important to know that the Moderna vaccine has been approved for individuals aged 18 and older, and the Pfizer vaccine for individuals aged 16 and older. Neither vaccine has been tested for effectiveness in people younger than those ages.

Widespread vaccination and what it means

The goal of the national vaccination plan is to create herd immunity through large-scale vaccination, said Kaushic, and it remains a top priority despite other unknown variables regarding mRNA vaccines. 

“What we really need to do is get people vaccinated as quickly as we can, so that everybody is protected, and to try to really decrease the number of infections that are in the community,” said Kaushic. 

Prolonged increased infection numbers could pose an entirely new problem for immunologists in the future, she continued.

“The more the virus replicates, the more chances it has for mutating,” said Kaushic. “We need to bring down our infection numbers and increase our vaccination numbers to make sure that there’s not enough chances for the virus to mutate itself outside of vaccine protection.”

With vaccine supply seeming to be facing limitations, the most recent report from the National Advisory Committee on Immunization (NACI) did note that there is a theoretical risk of developing a vaccine resistant strain of the virus in partially immunized individuals — those who do not receive the second dose within the recommended time frame — but no current evidence to confirms this is occurring.

There are also still many questions, including ones about the vaccine’s efficacy on asymptomatic infection and transmission, which is why Kaushic stressed the importance that Canadians continue to adhere to other public health orders even after being vaccinated.

“The vaccines are not a silver bullet. We don’t know, for example, how long vaccine protection lasts and we don’t know whether the vaccine protects people from getting an infection and transmitting [it],” said Kaushic. “If you’ve had both doses, you’re 95 per cent protected, but we still don’t know whether that means you can transmit that infection to other people, so the public health measures are still really important.”

For those looking to learn more about mRNA vaccines and the ongoing research around COVID-19 vaccines, Kaushic recommended several resources currently sharing accurate information — including Health Canada, NACI, the Coalition for Epidemic Preparedness Innovations, the #ScienceExplained series from COVID-19 Resources Canada and partners, and the World Health Organization.

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