Official News Magazine of the Canadian Snowbird Association


COVID-19 vaccines:

questions & answers

Despite the daily avalanche of COVID-19 stories in the news, people are still hungry for information. Vaccines, which hold out the promise of herd immunity and an eventual return to normal, are arguably top of mind for the average Canadian.

Vaccines are certainly top of mind for the folks at CSANews – so much so that we decided to look into the subject ourselves. After doing our due diligence, digging into the depths of the internet and separating fact from fiction, we’re sharing the results of our research with you.

What vaccines are available in Canada?

There are currently four vaccines available: Moderna, Pfizer-BioNTech, AstraZeneca/COVIDSHIELD and Johnson & Johnson (also known as Janssen).

What do they have in common?

All four COVID-19 vaccines help to protect you against SARS-CoV-2 (the virus that causes COVID-19) by teaching your immune system to recognize the virus and respond quickly if you become infected. They have been assessed in clinical trials involving thousands of people and are all effective in preventing serious illness that leads to hospitalization or death.

These vaccines have similar common side-effects (such as pain at the injection site, chills and feeling tired or feverish) and rare, serious side-effects such as allergic reactions. The AstraZeneca and Janssen vaccines both have one very rare side-effect: blood clots.

What makes them different from each other?

Three of the four vaccines require two doses. The fourth − the Janssen vaccine − requires only one dose.

The vaccines also work differently.

The Moderna and Pfizer-BioNTech vaccines are mRNA vaccines, a type of vaccine that teaches the body’s cells how to produce a spike protein that usually exists on the surface of the COVID-19 virus (see “How do mRNA vaccines work?”).

The AstraZeneca and Janssen vaccines instruct the body’s cells on how to produce the same spike protein, but go about it in a different way. These are known as vector vaccines. Both vaccines contain harmless vector viruses. A vector virus is a modified version of a virus (a harmless virus, not related to the COVID-19 virus). This modified virus contains instructions that cause cells in the body to produce the spike protein which appears on the surface of the COVID-19 virus.

Harmless in itself, the spike protein is key to “training” the immune system to recognize and attack the COVID-19 virus. The body responds to the presence of the foreign spike protein by making protective antibodies. Later, if you do get COVID-19, your body will recognize the spike protein on the coronavirus and the antibodies will work to protect you.

The vaccines are not all equally effective. Moderna and Pfizer-BioNTech are about 95% effective in preventing infection, while AstraZeneca and Janssen are in the 60% range.

The vaccines are approved for use in different age groups: Pfizer-BioNTech is approved for people 12 years of age and older, while the other three vaccines are approved for people at least 18 years of age.

How do mRNA vaccines work? RNA is a molecule that tells cells how to make proteins. The messenger RNA (mRNA) in the Moderna and Pfizer-BioNTech vaccines contains genetic instructions that tell a cell how to make the spike protein on the surface of the COVID-19 virus. The immune system recognizes the spike protein as something foreign and begins making antibodies that will fight COVID-19.

Can mRNA vaccines alter my DNA?

No. Your DNA is in the nucleus of your cells, and the mRNA vaccine never enters the nucleus. After a cell finishes using mRNA instructions to create the protein, the cell breaks down the instructions and gets rid of the mRNA.

When does my vaccine become effective? How long do I have to wait?

For the two-dose vaccines, immunity begins about two weeks after the first dose. The second dose boosts your immune response even more.

After I’m vaccinated, how long will my protection against COVID-19 last?

This question is still being researched. We don’t yet have the answer.

Why are the Moderna and Pfizer-BioNTech vaccines so much more effective than the AstraZeneca and Janssen vaccines? Does it have something to do with Moderna and Pfizer-BioNTech being mRNA vaccines?

While it’s true that Moderna and Pfizer-BioNTech claim efficacy rates about 30% higher than the other vaccines, it’s important to take these figures with a grain of salt. The vaccines were tested in separate clinical trials under different conditions, which might account for the difference in effectiveness.

Another thing to consider is what the efficacy rates from the clinical trials are measuring. The investigators were assessing whether or not the vaccines protected against any COVID-19 infections (even mild ones). What is most important, however, is preventing risk of serious illness. The vaccines are all nearly 100% effective in preventing COVID-19 that is severe enough to require hospitalization.

How worried should I be about getting blood clots from the AstraZeneca and Janssen vaccines?

It’s true that a few people who received these vaccines have developed blood clots, and some have died. However, this is a rare side-effect. Also, it’s important to note that COVID-19 causes blood clots (along with a lot of other nasty symptoms) when weighing the risks and benefits of receiving AstraZeneca or Janssen.

If I’ve received the AstraZeneca or Janssen vaccine, how do I know if I might have a blood clot?

This type of blood clot is linked to noticeable side-effects. Get immediate medical attention if you experience any of the following symptoms:

  • Shortness of breath
  • Chest pain
  • Swelling in the legs
  • Persistent abdominal (belly) pain
  • Neurological symptoms (such as severe or persistent worsening headaches or blurred vision)
  • Skin bruising
  • Tiny blood spots under the skin at places other than the injection site

Shouldn’t they be screening women for potential blood clotting before administering the vaccine?

It would not be practical to screen every woman for blood clots before getting vaccinated. The required medical tests would create delays.

The Janssen vaccine is only one dose. Wouldn’t it be more effective if I received two doses instead of one?

Scientists are working on this, but we don’t know yet. There is a clinical trial underway to test the effectiveness of two doses, but we will have to wait for the results before we know the answer to this question.

Can I “mix and match” vaccines? Would that be more or less effective, or somehow dangerous?

On June 1, the National Advisory Committee on Immunization (NACI) advised that Canadians who had received the AstraZeneca vaccine for their first dose be given the option to receive the Moderna or Pfizer-BioNTech vaccines for their second dose. Recent studies in Europe suggest that combining AstraZeneca and Pfizer-BioNTech may be as effective as two doses of Pfizer-BioNTech. Other evidence shows that two doses of Moderna or Pfizer-BioNTech appear to offer better protection against the Delta variant from India than two doses of AstraZeneca. We don’t yet know if a second dose of Moderna or Pfizer-BioNTech will provide better protection against Delta than two doses of AstraZeneca. It is being left up to individuals to make the decision for themselves. The NACI has also stated that people who have received an mRNA vaccine may receive a different vaccine for their second dose if the original vaccine is not available. For example, if you received Pfizer-BioNTech for your first dose, you can be given Moderna for your second dose if Pfizer-BioNTech is not available at the time of your second dose.

The government says to get the first shot you can, but isn’t Moderna the best?

The two mRNA vaccines (Moderna and Pfizer-BioNTech) have efficacy rates much higher than the viral vector vaccines (AstraZeneca and Janssen). If you have a choice, it’s fine to opt for an mRNA vaccine over a viral vector vaccine. However, many or most people won’t have that choice. If you don’t have a choice as to what vaccine to receive, it’s best to get vaccinated, because even a less-effective vaccine provides protection against COVID-19.

Is there anyone who shouldn’t get vaccinated for COVID-19? What about people with chronic diseases?

People who have had a severe allergic reaction to a vaccine (or to one of its ingredients) shouldn’t be vaccinated. For people with underlying medical conditions, vaccination can actually be more important than for healthy people, because there are many conditions which make it more likely that they would get seriously ill if infected with COVID-19.

I have allergies. Should I be worried about being allergic to the COVID-19 vaccine?

In most cases, the answer is “no.” If you are allergic, but the allergy is not related to vaccines, you can get vaccinated. This is true even if you are extremely allergic to non-vaccine-related triggers such as food, environmental factors or latex.

However, if you have had an allergic reaction to another type of vaccine or injectable therapy, even if it was mild, you should tell your doctor.

If you are allergic to polyethylene glycol (PEG) or polysorbate, this will affect the vaccine which you are able to get. PEG is an ingredient in both mRNA vaccines (Moderna and Pfizer-BioNTech); polysorbate is an ingredient in the viral vector vaccines (AstraZeneca and Janssen). If you are allergic to PEG, you should avoid the mRNA vaccines. If you are allergic to polysorbate, you should not receive a viral vector vaccine.

I think that my immune system is strong enough to handle COVID-19. Why should I get vaccinated?

Even if you’re willing to take your chances, you could infect others if you get sick. This is especially important if anyone in your circle has a higher-than-average chance of developing a serious case of COVID-19. That group includes health-care providers, older adults and people with different medical conditions (see “What are some of the underlying conditions or other factors that make people likely to experience severe illness when infected with COVID-19?”).

Will any vaccines besides the COVID-19 vaccines protect me against COVID-19?

So far, we don’t know. Researchers are exploring the possibility that existing vaccines (for example, the anti-tuberculosis Bacille Calmette-Guérin [BCG] vaccine) offer some protection.

Can I get infected with COVID-19 after I’m vaccinated?

The answer is more complicated than you might think. The research into the efficacy of vaccines tested whether or not they prevent disease, not whether or not you can become infected. At the moment, we’re not sure whether the vaccines protect against infection (although they do provide protection against severe illness that results in hospitalization and death).

If I get infected after I’m vaccinated, can I pass the infection along to someone else?

We don’t yet have the answer to this question. Until we do know, it’s best to err on the side of caution − continue to wear masks, practise social distancing and wash your hands.

What is “herd immunity”?

Herd immunity, also known as “population immunity,” occurs when the number of people immune to an infectious disease stops the disease from spreading through the population. A person becomes immune either through becoming infected with the disease or through vaccination. For a serious disease such as COVID-19, it’s obviously better to achieve herd immunity through vaccination. Allowing the disease to spread unchecked would mean that many people would get very sick and some would die.

What percentage of the population has to be vaccinated against COVID-19 to achieve herd immunity?

The answer is different for every disease. Measles requires 95% of people to be vaccinated in order to prevent infection from spreading, while for polio, the figure is 80%. For COVID-19, we don’t yet know the proportion of the population which needs to be vaccinated to prevent its spread. Until we do know, it’s important for as many people as possible to be vaccinated.

Why don’t we just vaccinate 100% of the population?

Some people can’t be vaccinated because of health conditions, such as being allergic to a vaccine or its ingredients.

What are some of the underlying conditions or other factors that make people likely to experience severe illness when infected with COVID-19?

Age, asthma, chronic kidney disease, chronic obstructive pulmonary disease (COPD), cystic fibrosis, damaged or scarred lung tissue, dementia, diabetes, Down syndrome, heart conditions (heart failure, coronary artery disease, cardiomyopathy, high blood pressure), HIV infection, weakened immune system, chronic liver disease, overweight and obesity, pregnancy, pulmonary hypertension (high blood pressure in the lungs), sickle cell disease, smoking (current or past), stroke, transplantation and substance use (drugs).

Can COVID-19 vaccines give me COVID-19?

No, because they do not contain the virus that causes COVID-19.

If I think (or know) that I have had COVID-19, how long should I wait before I get vaccinated?

You should wait until you are no longer infectious before you get vaccinated (otherwise, you might infect other people while getting your shot). If it’s 10 days after your symptoms first appeared, you’ve gone 24 hours without a fever or using fever-reducing medication (such as ibuprofen or acetaminophen) and your other symptoms are getting better, you will no longer be infectious.

If you were infected with COVID-19 but didn’t experience any symptoms, wait for 10 days after you tested positive before getting vaccinated.

What are “variants”? Are COVID-19 variants more dangerous? Can getting vaccinated protect me against these variants?

All viruses (including the SARS-CoV-2 virus) change over time. As viruses replicate (make copies of themselves), the copies may be slightly different than the original. These differences are known as “mutations.” A “variant” is a version of the virus with at least one mutation.

While most mutations don’t affect how infectious a virus is, or how serious an illness it may produce, some do. Variants with these sorts of mutations can be dangerous because they may spread more quickly and easily than previous versions of the virus, or may make people much sicker.

The COVID-19 vaccines that are currently available or being developed should provide at least some protection against variants of SARS-CoV-2 because of how they affect the immune system. These vaccines trigger a range of antibodies and cells, meaning that they may be less effective against some variants, but not completely ineffective. Scientists are following the variants. If it turns out that a vaccine is less effective against a particular variant, the vaccine will be altered to make it more effective against that variant.

Is it safe for me to get vaccinated if I’ve had COVID-19 and I’m a “long-hauler” who still has symptoms?

Generally speaking, it’s safe to get vaccinated if you had COVID-19 and still have symptoms, but are no longer contagious (“long-hauler”). There is no evidence that a COVID-19 vaccine will make long-haulers sicker or at greater risk of COVID-19 complications, so they should be vaccinated unless there is another reason why they should not get the vaccine.

I’ve already had COVID-19. Do I really need to get vaccinated?

Yes. Although having COVID-19 may provide you with some protection against reinfection, it’s uncertain how long this protection might last. As there is a possibility of becoming reinfected, and COVID-19 can have serious health consequences, it is recommended that you be vaccinated after you have recovered from COVID-19 and are no longer infectious.

If I get the vaccine, will I test positive for COVID-19 when I do a PCR test?

No, you won’t test positive after receiving the vaccine.

Shouldn’t they be screening people for COVID-19 before they administer the vaccine?

They do. Every person who receives the vaccine is first asked a series of questions. Some of these questions are designed to screen out people who are experiencing symptoms characteristic of COVID-19.

People are not tested before being vaccinated because it would slow down the process of getting as many people vaccinated as soon as possible.


COVID-19 Articles


(416) 441-7028 • 1-800-326-9560 •

©Medipac Communications