After Your Vaccination

The following information was developed for this website by medical professionals and public health experts using Canadian government and other scientific and medical sources. It is not intended as medical advice. Always seek the advice of a qualified healthcare provider with any questions you may have regarding the COVID-19 vaccine.

Last revision: 2021-08-13

We do know that the vaccines will protect people from getting very sick from the virus, but it’s possible that you could still carry the virus and be contagious to others even though you are fully vaccinated with 2 doses. The good news is that these breakthrough infections are likely to be mild and will prevent you from being hospitalized. We will learn more as the clinical trials continue and real-world evidence emerges. In the meantime, we’ll need to continue wearing our masks, practice physical distancing, and keep following public health recommendations until enough people are fully vaccinated.

It takes about two weeks after the second dose for the body to build immunity after vaccination. Someone could be infected with the virus just before or just after vaccination and get sick, because the vaccine didn’t have enough time to provide protection.

This is also why a full series of two doses of the vaccines are required.

The COVID-19 vaccines’ initial effectiveness is already very high after the first dose (80-92%) and lasts for at least a few months.

Experience with other multi-dose vaccinations after a single dose suggest persistent protection could last six months or longer. In fact, many studies have shown that you get an even better booster immune response the longer you wait. So this is backed by science. 

And for most vaccines, antibody levels (immunity) will go down over time and do not suddenly fall below protective levels. Even months or years later, another vaccine dose can boost immunity to higher levels, giving a longer duration of protection.

Now that we have much more reliable vaccine supply in Canada, the timeline between doses has been decreased to 4-8 weeks.

Yes, for now, until the Public Health Agency of Canada determines when the right time is to do away with masking and distancing. The newer variants, some of which are highly transmissible, can still cause serious infections in unimmunized and partially immunized people, so we should all do our part by protecting those who can’t yet get vaccinated (eg kids <age 12) and people with compromised immune systems who may not mount a strong enough protective response to vaccines.

We don’t know yet how long protection lasts for those who are vaccinated. Studies on the mRNA vaccines currently show that people who were vaccinated had a very strong immunity to COVID-19 for at least six months. It looks like immunity will last a while, but studies need to follow this over time.

At this point, we’re not sure if immunity will last a year or ten years, or if there will be a need for a booster shot at some point.

It usually takes a few weeks for the body to build immunity following COVID-19 vaccination. But remember that two doses are required in order to achieve the best immunity from the Pfizer-BioNTech, Moderna and AstraZeneca COVID-19 vaccines. The Johnson & Johnson COVID-19 vaccine only requires one dose.

After vaccination, it is common to have temporary mild or moderate side effects, including: 

  • Pain, redness, warmth, itching or swelling at the site of injection,
  • Fatigue,
  • Headache,
  • Nausea,
  • Muscle or joint pain, and
  • Mild fever or chills.

These are normal signs that your body is building protection and these symptoms should go away within a few days. 

If your symptoms are significant or worsening, consult your health care provider. If they are consistent with COVID-19, you should get tested and self-isolate until test results are available.

Very rarely, a more serious side effect called anaphylaxis may occur. This generally occurs within several minutes or the first hour after vaccination. For this reason, people receiving their COVID-19 vaccine are asked to remain for at least 15 minutes following vaccination so that health care personnel can monitor individuals for any serious reactions.

Side-effects are not an indication of whether or not the vaccine is working.

It is true that side effects are normal signs that the vaccine is working and your body is building protection. However, this doesn’t mean you should be worried if you don’t have side-effects. For example, the mRNA vaccines provided protective immunity to over 90% of recipients in the clinical trials, but more than 50% reported no side-effects. In other words, most people did not experience any reactions, but had full immunity.

So, if you didn’t feel any side effects after your COVID-19 vaccine, it’s not something to worry about—you still have the same protection as someone who experienced a side-effect!

Breakthrough infections do occur but before the arrival of the delta variant, they have been rare – around 0.5% of reported COVID-19 cases; and when post-vaccination infections do happen, they typically tend to be mild. While no vaccine offers 100% protection for every single person, the relatively infrequent examples of serious infections after full vaccination — coupled with the dramatic drop in cases, hospitalizations, and deaths from COVID-19 — show these vaccines are indeed doing a very good job. Eventually we will all be able to “live with COVID” without causing avoidable severe illness or death or overwhelming our healthcare systems.

Myocarditis is an inflammation of the heart muscle. Pericarditis is an inflammation of the sac around the heart.

There have been rare cases of this inflammation in young people after vaccination with mRNA vaccines (approximately 12 cases per million 2nd doses of any mRNA vaccine in the 21 days following vaccination).

Symptoms can include fatigue, chest pain, shortness of breath, palpitations, and fainting. 

It is more common in males, esp males age 16-24, and develops approximately 4 days after their 2nd dose. This is easily diagnosed and treated in hospital, and people generally recover from symptoms and do well.

NACI guidance says that individuals who experienced myo/pericarditis after first dose of mRNA vaccine should wait to get their second dose until more information is available. Informed consent for those receiving an mRNA vaccine should include a discussion of this very rare risk. 

It’s important to remember that this potentially rare and mild/quickly recoverable side effect is much rarer than the potential risks of COVID-19, including “long COVID”. And COVID-19 infection itself can cause myocarditis, similar to other viral infections.

Yes. It is normal to have a stronger reaction after the second dose because that’s when your immune system really kicks into gear. That big immune response is what causes the stronger reaction. It’s called a boosting phenomenon, and it builds an even greater ability to fight off COVID-19.

Here’s how it works:

When you get the first dose, your body learns to make COVID-fighting antibodies. Then you get the second vaccine, and you already have the antibodies ready to go, so that shot kicks them into action. That more robust immune response accounts for the stronger reactions. Those reactions tell you the vaccine is working. Although stronger reactions after the second dose are common, experts say some people may have little or no reaction.

To help with the stronger side effects, it’s OK to take Tylenol or other over-the-counter pain relievers after your shot – but not before – to help ease discomfort.

And remember that not everyone has a similar response to either dose. Just because you have little or no side effects, doesn’t mean that the vaccine hasn’t done its job!

At this time, there are no plans for Canadians to require a booster dose after they have been fully vaccinated with 2 doses of vaccine. There are a few countries that are planning to offer booster doses, but this is not supported by WHO. The pandemic is global, and there are still many countries where many people have not received even 1 dose of vaccine yet.

If future variants arise that evade the immune response created by our current vaccines, there is certainly a role for booster does in Canada to protect us from severe illness and death caused by these variants, but in the meantime, we have enough protection to keep us out of hospitals.