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Frequently Asked Questions about the COVID-19 Vaccine

Niagara Region Public Health and Emergency Services is closely monitoring the COVID-19 pandemic. This is an evolving situation and we'll continue to update information as it becomes available.

Updated Nov. 15

Second dose

  • Why do I need a second dose?

    It's great that you got your first dose of the COVID-19 vaccine. You need to get a second dose to complete your vaccination series and be fully vaccinated. You're better protected with both doses. Data shows that those who are fully vaccinated are less likely to develop a COVID-19 infection than those who aren't. Learn about COVID-19 infection in vaccinated versus unvaccinated individuals on our monitoring statistics page.

    The first dose of a two-dose vaccine series lets your body's immune system know what it needs to do to fight COVID-19. The second dose is the one that really gives your immune system optimal protection.

    At this time, the province has made some groups eligible for a third dose or booster dose. Learn who is eligible for a third dose or booster dose and the required proof of eligibility.

  • It has been more than four months since my first dose. Can I still get a second dose or do I need to restart my vaccination series?

    Full vaccination is the greatest protection you can have against COVID-19 and its variants. It's not recommended that individuals wait.

    If it's been more than four months since your first dose, you don't need to restart the series. However, Public Health does recommend you get your second dose as soon as possible to ensure maximum protection.

  • My first dose was AstraZeneca. What will happen with my second dose?

    If you received your first dose of AstraZeneca, you did the right thing to prevent the risk of infection and death from COVID-19 as early as possible. AstraZeneca is safe and effective to prevent COVID-19 and it reduces the risk of infection and death from COVID-19.

    For your second dose, the province indicates that you may get an mRNA vaccine (Moderna or Pfizer) as your second dose. The National Advisory Committee on Immunization recommends an mRNA vaccine for a second dose due to emerging evidence including the possibility of better immune response and the safety of mixing vaccine brands for first and second doses. This will count as a completed COVID-19 vaccination series.

    On June 14, 2021, the province updated the second dose interval to as early as eight weeks for those who got a first dose of AstraZeneca. This is based on studies that show dosing intervals between eight and 12 weeks is safe and gives a beneficial immune response.

    There is evidence that a longer interval between two doses of the AstraZeneca vaccine (such as a 12-week interval) gives higher protection. However, some may choose to get their second dose sooner to have the increased protection that the second dose gives earlier.

    We encourage you to speak with a health care professional for help understanding the options available so you can make an informed decision on your vaccination.

    Completing your vaccination series with an mRNA vaccine:

    • The concept of using different vaccine products to complete a vaccine a series is not new
    • Studies show that a first dose of AstraZeneca followed by a second dose of mRNA vaccine is safe and will boost your immune response against COVID-19 for that long-term protection. These studies used Pfizer as the second dose.
    • Countries in Europe including Denmark, Finland, France, Germany, Norway, Spain and Sweden have already been offering either Moderna or Pfizer to those who had a first dose of AstraZeneca
    • With an mRNA as your second dose, there is evidence of increased short-term, mild side effects such as headache, fatigue and feeling generally ill. These symptoms don’t last long and resolve without complications.

    If your first dose was the AstraZeneca vaccine, and you’d like to receive an mRNA vaccine (Moderna or Pfizer) as your second dose:

  • What are side effects like after a second dose?

    Side effects after your second dose can be similar to the ones you may have had after your first dose but they only last about one to three days. These symptoms typically mean that your body is building protection. If you don't get the second dose, you won't be fully protected from COVID-19.

Third doses and booster doses

General information

Vaccine safety

We know you want to be sure that COVID-19 vaccines are safe. To help you decide if the vaccine is right for you, watch Dr. Hirji answer questions about vaccine safety.

  • How do I know that I won't get COVID-19 from the vaccine?

    There is no COVID-19 virus in the vaccine. The vaccines teach your immune system how to recognize and fight the virus that causes COVID-19.

    Some people may develop mild side symptom such as fever. These symptoms typically mean the vaccine is working to produce protection. It usually takes the body a few weeks to build immunity after receiving a vaccine.

    You can become infected with the virus before or right after getting the vaccine. This happens because the vaccine has not had enough time to provide protection in your body.

  • What do I need to know about the long-term safety of mRNA vaccines?

    From the science and history of vaccines, there is no evidence of long-term effects.

    Vaccine side effects usually happen within a few days, and always within six weeks. Vaccines are quickly broken down and removed from your body, and so cannot cause side effects many months or years later. The only lasting impact of vaccination is the training it provides your immune system.

    Vaccines introduce proteins from a dangerous germ to the body’s immune system. In this way, the body can learn to identify and fight those germs off. Within a couple of weeks, no traces of the vaccine are left in the body. This is because the immune system destroys the proteins. Any other elements of the germ are quickly broken down.

    Like any medication or supplement (including vitamins), there’s a chance that there will be a serious side effect. These are rare, but they do happen. When it does, it's usually in the short term when the vaccine is stimulating the immune system. Learn about how Canada makes sure vaccines are safe for you and your family.

    It's far more likely that mRNA vaccines will be like other vaccines. Here's what you need to know about mRNA vaccines:

    • mRNA vaccines are a new vaccine platform, but not a new technology. mRNA therapeutics have been studied for over two decades. Recent scientific advancements have improved mRNA stability and delivery. This has allowed mRNA vaccines and cancer mRNA therapeutics to be put into clinical use.
    • mRNA vaccines provide instructions to the body to produce a coronavirus protein. The body then recognizes the protein as foreign. These proteins use the body's normal processes to safely produce an immune response. As soon as it is finishing using the mRNA's instructions, the body breaks down and gets rid of the mRNA.
    • Once the mRNA breaks down, the body doesn’t have the ability to produce more of this foreign mRNA. So there’s nothing left of the vaccine long-term. The only long-term impact of the vaccine is immune memory against COVID-19.
    • The safety of COVID-19 vaccines are closely monitored. Any safety issues are responded to right away and Canadians are informed about any risks that arise.
  • How do I know that the vaccine won't change my DNA?

    The vaccine doesn't change your DNA in any way.

    The mRNA from a COVID-19 vaccine never enters the nucleus of the cell, which is where our DNA are kept. This means the mRNA doesn't affect or interact with our DNA in any way. Instead, COVID-19 vaccines that use mRNA work with the body's natural defences to safely develop protection (immunity) to disease.

  • Can I get the vaccine if I have a health condition?

    People with health conditions can get vaccinated. Conditions include: diabetes, high blood pressure, heart disease, respiratory diseases, including asthma or COPD, hepatitis B, C and HIV.

    People with a weak immune system because of illness, treatment or an autoimmune condition should also be vaccinated. However, they may receive lower protection from the vaccine.

    Watch family physician, Dr. Dec, talk about the importance of people who have a health condition getting vaccinated.

    Certain immunocompromised individuals are eligible for a third dose. Learn who is eligible for a third dose or booster dose and the required proof of eligibility.

  • How were the COVID-19 vaccines developed so fast?

    The rapid development was made possible by decades of advances in vaccine technology. Specific research into coronaviruses gave a head start to developing a COVID-19 vaccine. Watch COVID-19: How vaccines are developed.

  • If I had a reaction to a different vaccine in the past, can I still get the COVID-19 vaccine?

    Most people who had a reaction to a prior vaccine can safely receive the COVID-19 vaccine. Check with your doctor or health care provider if you have had a serious allergic reaction to a vaccine in the past. They will look at your medical records and advise you accordingly.

  • Is it acceptable for someone with food or seasonal allergies to receive the COVID-19 vaccine?

    Yes. If you have allergies that are not related to any components of the COVID-19 vaccine, you can still be vaccinated.

  • Who should not get the vaccine?

    People who have had a serious allergic reaction, such as anaphylaxis, to a component of the COVID-19 vaccine cannot receive the vaccine. Others who have had a less serious, but immediate allergic reaction, should see their health care provider for guidance.

    Viral vector vaccine

    AstraZeneca is a second dose option only for those who received it as a first dose and are 40 years of age or older. However, you cannot get AstraZeneca as a second dose if you have:

    • A history of capillary leak syndrome
    • Experienced venous or arterial thrombosis with thrombocytopenia following vaccination with a viral vector COVID-19 vaccine

    See "My first dose was AstraZeneca. What will happen with my second dose?" in the second dose section.

    mRNA vaccine

    • If you have an allergy to polyethylene glycol, you should not get vaccinated if your past reaction was severe
    • If you experienced myocarditis (heart inflammation) and / or pericarditis (inflammation of tissue around the heart) after a first dose of an mRNA vaccine, you should wait to get your second dose until more information is available
  • What do I need to know about reports of myocarditis (heart inflammation) and/or pericarditis (inflammation of tissue around the heart) and COVID-19 vaccination?

    Both myocarditis and pericarditis are more common after COVID-19 illness (a viral infection) than after vaccination.

    While there have been rare reports of myocarditis / pericarditis after vaccination, the majority of cases have been mild, easily treated and individuals recover quickly.

    Learn more about myocarditis / pericarditis and COVID-19 vaccines.

Getting ready for your vaccine appointment

After being vaccinated

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