COVID-19: Vaccines

For other public health concerns (flu, hepatitis A, etc.) people have safely been given a first dose of one vaccine and a second dose of a different vaccine. In order to be extremely cautious, the Canadian governments waited until information was available on doing this with COVID-19 vaccines. So far, this practice has been both safe and effective at preventing COVID-19.

The government of Ontario recommends that people who received a first dose of AstraZeneca receive AstraZeneca, Moderna, or Pfizer as a second dose, based on personal preference. People in other countries have done this, and what we know so far suggests that this has been both safe and effective at preventing COVID-19.

If you received a first dose of Moderna or Pfizer, it is recommended that you get the same vaccine for your second dose. However, the Ontario government recommends that these two vaccines may be ‘mixed and matched’ if supply is not available for the original vaccine you got.

With the spread of the Delta variant, children are at increased risk for severe disease, hospitalization, and death from COVID-19. All eligible children should be vaccinated as soon as possible to protect them from this more contagious and more severe variant of COVID-19.

For more information on COVID-19 vaccinations in children and youth see COVID-19 vaccine for children and youth (Canadian Pediatric Society) or FAQs: Covid-19 mRNA Vaccines for Children (University of Waterloo)

Yes. The clinical trials for the Pfizer and Moderna vaccines showed that they are safe for children. Just like adults, many children had short-term, non-serious side effects like arm pain, fatigue, headaches, chills, muscle pain, fever, and joint pain.

Yes. Clinical trials showed 100% efficacy in children 12-15 (Pfizer) and 12-17 (Moderna) years of age. Clinical trials in children ages 5-11 (Pfizer) showed 90.7% efficacy.

This depends on which Public Health Unit you live in, as some units require parental consent and others do not. See Provincial vaccine rollout for links to all Public Health Unit websites.

In Ontario, there is no defined age of consent for vaccinations. Generally, children can consent to medical treatments as long as they are deemed capable of making an informed decision. This means that they must be able to understand information about the vaccine and what will happen if they accept or refuse vaccination.

A very small number of cases of Guillain-Barré Syndrome (GBS) have occurred in people who received the AstraZeneca COVID-19 vaccine. Fortunately, most people eventually recover from even the most severe cases of GBS. If you received your first dose of AZ over 25 days ago and have no symptoms, you are unlikely to be at risk for GBS as a result of receiving the vaccine. 

A very small number of cases of capillary leak syndrome (CLS) have occurred in people who received the AstraZeneca COVID-19 vaccine. CLS is a very rare, serious condition that causes fluid leakage from small blood vessels.

The chance of CLS occurring is very low, but you should still be aware of the symptoms so that you can get fast medical treatment if it happens. Seek medical attention immediately if you have the following symptoms in the days after vaccination, in combination with feeling faint:

• rapid swelling of the arms and legs
• sudden weight gain

The AstraZeneca vaccine is associated with extremely rare cases of blood clots. These cases represent a small fraction of millions of doses delivered. While the cases are concerning enough to need investigation, it’s important to remember that the risk is very small, especially compared to the proven high risk of blood clots associated with COVID-19 infection.

If you received the AstraZeneca vaccine:

• More than 28 days ago: there is no cause for concern for blood clots.
• Less than 28 days ago: It is important to look for symptoms for 28 days, as it is easier to treat these rare clots if they’re found early. Seek immediate medical attention if you develop:
  • shortness of breath
  • difficulty speaking
  • severe chest, back or abdominal pain
  • new severe swelling, pain or colour change in an arm or leg
  • sudden onset of severe or persistent worsening headaches or blurred or double vision
  • unusual bleeding or bruising (other than at the site of vaccination)
  • new reddish or purplish spots or blood blisters
  • seizure
  • difficulty moving part of your body

Adverse events are extremely rare following the AZ vaccine. For those who have already been vaccinated with AstraZeneca:

• More than 28 days ago: there is no cause for concern for blood clots or GBS.
• Less than 28 days ago: It is important to look for symptoms for 28 days. See the AstraZeneca/GBS and AztraZeneca/blood clots questions above for information on monitoring symptoms.

Focus on the benefits of the vaccine. During the 28 days after receiving the vaccine, your body is building up powerful immunity against COVID-19. There are also free online services for COVID-19 anxiety such as Wellness Together or MindBeacon that offer support groups, mindfulness, or therapy. You can also call 211 Ontario (2-1-1) to find local stress and mental health supports in your area.

No, you should not wait. The Pfizer and Moderna vaccines are very similar in how they work and how effective they are against COVID-19. Both are mRNA vaccines, and in clinical trials, they showed almost the exact same efficacy after one dose (92.6% for Pfizer and 92.1% for Moderna) and two doses (95.0% for Pfizer and 94.1% for Moderna).

The Pfizer and Moderna vaccines are indeed very similar. Hesitancy around the Moderna vaccine is likely due to people being more familiar with Pfizer as a company. It also may be because Canada has received many more Pfizer vaccines compared to Moderna. But the differences in quantities of vaccines are due to logistics, and have nothing to do with the effectiveness or safety of either vaccine.

A very small number of cases of Guillain-Barré Syndrome (GBS) have occurred in people who received the Pfizer and Moderna COVID-19 vaccines. GBS is a very rare condition where your body’s immune system damages nerve cells. Fortunately, most people eventually recover from even the most severe cases of GBS.

At this time, the rate of GBS among people who received the Pfizer and Moderna vaccine is very low and is not higher than what is normally expected. However, you should still be aware of the symptoms so that you can get fast medical treatment if it happens. Seek medical attention immediately if you have the following symptoms in the days after vaccination:

• Weakness or tingling sensations, especially in the legs or arms, that’s worsening and spreading to other parts of the body
• Difficulty walking
• Difficulty with facial movements, including speaking, chewing, or swallowing
• Double vision or inability to move eyes
• Difficulty with bladder control or bowel function

The benefits of getting the Pfizer and Moderna vaccines continue to outweigh the harms. The important thing is protecting yourself from the very real risks of COVID-19 and all the vaccines approved in Canada will do that. Let’s talk about it and come to a decision together.

The purpose of all COVID-19 vaccines is to imitate the virus without making you sick. That way, your immune system can recognize the COVID-19 virus and stop future infections.

mRNA is something that your cells naturally use, every second of every day. mRNA is the recipe that tells your cells how to make proteins.

A COVID-19 mRNA vaccine has mRNA that tells your cells how to make the “spike protein” found on the outside of the COVID-19 virus. This spike protein cannot make you sick.

Your immune system “reads” the spike protein that our cells made, and builds antibodies and white blood cells to fight it. Then if you are infected with COVID-19, your immune system will recognize the spike protein that covers each virus, and can fight off the infection.

Your body quickly destroys the vaccine after making spike proteins. It does not stay in your body for long and does not make any long-term changes, other than helping you build your antibodies and white blood cells.

No. mRNA vaccines cannot change your DNA. Human beings do not have the enzymes to convert RNA into DNA. The vaccine doesn’t contain those enzymes either. In fact, our cells have enzymes that destroy the mRNA after the protein is made – which is why the vaccine doesn’t stay in your body for long.

Reports show that a small number of people experienced mild heart inflammation after receiving an mRNA vaccine in Canada and around the world. So far, the cases are more common in teenagers and young adults, males than females, occur after the second dose of the vaccine and typically happen within seven days after vaccination.

Viruses, and the body’s immune response to infection, typically cause this type of heart inflammation. It is important to know that this condition is rare, often has no symptoms, heals on its own, and is easily treated.

If you or someone you know experience the following symptoms after receiving an mRNA vaccine, seek medical attention: chest pain, shortness of breath, or feelings of having a fast-beating, fluttering, or pounding heart.

The purpose of all COVID-19 vaccines is to imitate the virus without making you sick. That way, your immune system can recognize the COVID-19 virus and stop future infections.

A COVID-19 viral vector vaccine has a piece of DNA (a gene) that tells your cells how to make the “spike protein” found on the outside of the COVID-19 virus.

In order to get the spike protein DNA into your cells, the DNA is placed in a hollow, harmless virus that is not COVID-19. This virus is called a viral vector, and it cannot make you sick.

Once in your cells, the DNA tells your cells how to make the spike protein. The spike protein cannot make you sick.

Your immune system “reads” the spike protein that your cells made, and builds antibodies and white blood cells to fight it. Then if you are infected with COVID-19, your immune system will recognize the spike protein that covers each virus, and can fight off the infection.

Your body quickly destroys the vaccine after making spike proteins. It does not stay in your body for long and does not make any long-term changes, other than helping you build your antibodies and white blood cells.

No. Viral vector vaccines cannot change your DNA. Human beings do not have the enzymes to insert the vaccine DNA into our DNA. The vaccine doesn’t contain those enzymes either.

COVID-19 is much more serious than the flu. The risk of death is 3.5 times higher for COVID-19 than influenza (CMAJ, 2021).

COVID-19 is very contagious and can cause serious illness. More than 28,000 Canadians and over 728,000 Americans have died of COVID-19.

Even if a young and healthy person does not die of COVID-19 infection, they may have long term complications from COVID-19, affecting multiple organ systems. Long-term effects include memory loss, fatigue, body aches, unexplained breathing difficulties, and damage to the lungs and heart. Clinics have already been set up to support the many COVID-19 patients who, although they are no longer infected, cannot go back to work or live a normal life.

Even if a young and healthy person does not develop severe COVID-19 infection, you may still pass on the virus to someone who will. If you are vaccinated, you’re helping protect the people around you. Vaccination is the only way to end this pandemic. Vaccination helps protect against serious disease. I and all the members of the healthcare team around you have been immunized. You can protect yourself, your loved ones, and your community by getting vaccinated.

Even if you had COVID-19 in the past, it is uncertain how long the antibodies will last. You should still get the vaccine to protect yourself and others.

At this time, we know that it typically takes a few weeks for the body to develop immunity after vaccination. Therefore, it is possible that a person could be infected with the virus that causes COVID-19 just before or just after vaccination and then get sick because the vaccine did not have enough time to provide protection.

That being said, we also know that the vaccines protect most vaccinated people from getting sick with COVID-19. For those who still get sick, they appear to get a milder case. However, studies are ongoing as to how the vaccine affects how contagious infected people are.

It is important to continue public health measures of distancing and masking even after vaccination, until scientific experts say it is safe to stop.

Regular exercise and healthy eating can improve your immune system and overall health. But neither can cause your body to produce the antibodies and white blood cells that specifically protect you from COVID-19. Your immune system needs to be trained to produce these, and all approved COVID-19 vaccines help your immune system do this, regardless of the type of vaccine (e.g., mRNA, viral vector, etc.).

There is no evidence that homeopathic treatments can prevent COVID-19 or any other infections (Health Canada, 2019).

All of the COVID-19 vaccines approved in Canada are safe and highly effective for use in pregnant and breastfeeding people. The social media rumours about the vaccines affecting fertility or the vaccines putting pregnant people at an increased risk of an extremely rare blood clot are untrue. There is no scientific evidence to support either of these rumours.

People who are pregnant are at higher risk of serious adverse events from COVID-19. It is strongly recommended that all pregnant individuals get vaccinated against COVID-19. Let’s discuss the benefits and risks and come to a decision together.

All COVID-19 vaccines are safe and effective for older people. Getting the vaccine is an important step to help prevent becoming sick with the virus.

Serious adverse events and anaphylaxis are very rare with the COVID-19 vaccines, occurring in only 0.006% of doses given. Unless you have a history of allergic reaction to components of the vaccine, or to the first dose of the vaccine, Health Canada recommends vaccination.

It is always advised to wait at least 15 minutes after receiving a vaccine, since an allergic reaction or anaphylaxis is always a possible reaction to any medication or vaccination. For those with a history of allergies, even to food, pets or other non-medical causes, waiting 30 minutes after receiving a vaccine is recommended.

Some patients may be allergic to an ingredient in one, but not another. On this site you can also review the vaccine ingredients in non-medical terms for the Pfizer-BioNTech, Moderna.

For references and further information, see our Top Resources.

It is important that new vaccines be tested in diverse populations to ensure that they are safe and effective for everyone. All COVID-19 vaccine trials included people of colour who were both racially and ethnically diverse. Collectively, the trial participants included those identifying as Black, American Indian/Alaska Native, Asian, Native Hawaiian/other Pacific Islander, Hispanic/Latino and multiracial.

Yes, you can take all of the approved vaccines. None of the approved vaccines in Canada contain live viruses, and neither do any of the vaccines that Canada has purchased but not yet approved.

For more information on the different types of COVID-19 vaccines, see Types of COVID-19 vaccines.

The Canadian Council of Imams and other Muslim bodies in Canada have stated that they consider the Pfizer-BioNTech, Moderna, and AstraZeneca vaccines to be permissible and will continue to evaluate other approved vaccines (Canadian Muslim COVID-19 Taskforce, 2021).

The Canadian Conference of Catholic Bishops have stated that all approved COVID-19 vaccines are permissible for Catholics. They indicate that Catholics are invited to be vaccinated to contribute to the safety of others (Canadian Conference of Catholic Bishops, March 11, 2021).

Some patients may have questions regarding their religion and receiving COVID-19 vaccines.

Many religious organizations have issued statements that encourage COVID-19 vaccination for the health and safety of individuals and their communities, following the advice of patients’ healthcare providers.

These organizations include:

• The Vatican and the Canadian Conference of Catholic Bishops
• Muslim American Society
• Canadian Muslim COVID-19 Task Force
• World Jewish Congress and World Council of Churches
• Orthodox Union and Rabbinical Council of America

While no research has been done to look specifically at whether COVID-19 vaccines are affected by Tylenol or Advil, earlier research has suggested that some drugs may affect immune response to other vaccines. To ensure the vaccine works properly, don’t take Tylenol or Advil immediately before your vaccination appointment. It’s ok to take either of these medications to reduce discomfort in the days after your vaccination.

No. As the vaccines target the immune system, they will not interact with medications such as statins. While certain immunosuppressants may slightly reduce the efficacy of the vaccine, there are no known drug interactions that will cause harm, prevent medications from working, or prevent the vaccine from working. There are some drugs not recommended to be taken with “live” vaccines, however no live vaccines are being considered for approval in Canada.

Your appointment for your second dose must be at least:

• 8 weeks after your first dose of AstraZeneca
• 28 days after your first dose of Moderna or Pfizer

The timing of your second dose appointment will depend on local considerations, vaccine supply, and the date of your first dose appointment. To book your second dose appointment, visit the provincial booking system.

• The pandemic – and the lockdowns and public health measures – will not end until the majority of Canadians are vaccinated. To ensure we can vaccinate everyone as quickly as possible, it is important that people access the vaccine the first time it is offered to them.
• Canada has ordered more than enough vaccines – we have purchased more shots per person than any other country in the world! We will be getting those vaccines delivered over time. The implementation plan of those vaccines is designed to most efficiently end this pandemic. You can feel confident that when you are offered one, it is because it is the right time for you to get it. This is your chance to do your part to end the pandemic and get back to normalcy quickly.
• If you wait to get vaccinated and get infected in the meantime, you may end up in hospital – which would put more strain on the system than getting the vaccine.
• If Canadians wait to get the vaccine, the pandemic will keep going – and that includes the restrictions, inability to see family and friends, send your kids to school, travel.
• If Canadians wait to get the vaccine, more people will die.

For references and further information, see our Top Resources.

• No steps were skipped in the process of developing, testing, approving, and producing the vaccines.
• Canada’s best independent scientists have thoroughly reviewed all the data before approving the vaccines as safe and effective for Canadians.
• The vaccines were produced faster than before not because of skipped steps but because of never-before-seen levels of collaboration and funding around the world invested in this effort. Normally, vaccine clinical trials need 6000-8000 people for the approval process.
  • The Pfizer-BioNTech trial had over 43,000 people.
  • The Moderna trial had over 30,000 people.
  • The AstraZeneca trial had over 11,000 people.
  • The Johnson & Johnson trial had over 44,000 people.

• Unlike with other vaccines that go one step at a time and then plan the next step, for the COVID-19 vaccines, governments invested in having companies plan all the steps at the beginning and build up their manufacturing capacity right away.

For references and further information, see our Top Resources.

The use of mRNA and viral vectors for vaccines and treatment of disease has been around for a while – that’s one of the reasons why these vaccines could be developed so quickly. mRNA vaccines have been used in animal models for influenza, Zika, Rabies, CMV and others, and in humans for cancer treatment and cancer vaccine clinical trials. Viral vector vaccine technology has been used for Ebola outbreaks, and a number of studies have focused on viral vector vaccines against other infectious diseases such as Zika, flu, and HIV.

For references and further information, see our Top Resources.

• The pharmaceutical companies manufacture the vaccine and sponsor and conduct the clinical trials, but all vaccine clinical trials must have an independent data and safety monitoring board review the vaccine efficacy and unblind the data.
• As the trial is completed, Health Canada reviews all safety and efficacy data before allowing the vaccine to be used in the Canadian population.
• After a vaccine has been approved for use and made available, its safety is continuously monitored by healthcare providers and Canada-wide networks specifically designed for safety. Health Canada monitors national and international vaccine safety reports and will update information about the vaccine as it becomes available.

Health Canada provides ongoing safety monitoring for the vaccines. You can see the most recent data at reported side effects following COVID-19 vaccinations in Canada (Health Canada)

For references and further information, see our Top Resources.

• The vaccines cannot give you COVID-19 or any other infectious disease. None of the licensed vaccines so far use the live virus that causes COVID-19.
• It is still possible to contract COVID-19 after you have been vaccinated. Like with other vaccinations, it takes a few weeks 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.

References

• Pfizer-BioNTech COVID-19 Vaccine Info Sheet (MOH, December 13, 2020)
• Details for: Pfizer-BioNTech COVID-19 vaccine (Health Canada, Nov 13, 2020)
• Consumer information: Details for Moderna COVID-19 vaccine / vaccin de Moderna contre la COVID-19 (Health Canada, Dec 23, 2020)
• Viral Vector-based Vaccines for COVID-19.

• With any of the approved vaccines people can expect to feel a sore arm, a bit of tiredness and a mild headache as the vaccine starts to work. Some people will feel muscle aches, chills, or a mild fever.
• For more information on how common side effects were in the Pfizer-BioNTech clinical trial, see its Clinical trial details.
• For more information on how common side effects were in the Moderna clinical trial, see its Clinical trial details.
• For more information on how common side effects were in the AstraZeneca clinical trial, see its Clinical trial details.
• For information about AstraZeneca and rare blood clots see questions about the AstraZeneca Vaccine
• For more information on how common side effects were in the Janssen clinical trial, see its Clinical trial details.

References

• Product monograph, including patient medication information: Pfizer-BioNTech COVID-19 vaccine (February 8, 2021)
• Product monograph, including patient medication information: Moderna COVID-19 Vaccine (Moderna, December 2020)

• Among the almost 22,000 vaccinated with the Pfizer-BioNTech COVID-19 vaccine, there were 4 cases of Bell’s palsy. This number of Bell’s palsy cases is consistent with the expected rate in the general population and did not suggest it was caused by the vaccine. Three cases occurred within one month after both doses were completed, and one case occurred later than one month after both doses were completed, and all four patients recovered.
• More research will be conducted as this was the only “imbalanced” occurrence that happened more in the vaccine arm of the study than the placebo arm.
• Those with previous history of Bell’s palsy may still take this vaccine.

References

• Vaccines and Related Biological Products Advisory Committee Meeting December 10, 2020 FDA Briefing Document Pfizer-BioNTech COVID-19 vaccine
• Product monograph, including patient medication information: Pfizer-BioNTech COVID-19 vaccine (February 8, 2021)
• Fact check: Clarifying claims around Pfizer vaccine deaths and side effects (Reuters, December 10, 2020)

• Yes. Mild side effects are common for all vaccines.

• There could be soreness and swelling which for some might be significant (sometimes from shoulder to elbow). In these cases:
  • Use cold compresses over the site.
  • Know that local reactions, even big ones, improve by 48-72 hours. If the reaction worsens at 72 hours or has not disappeared in 5 days, seek medical attention.
  • Even though sometimes this reaction can look like an infection, the risk of skin/local infection from a vaccine needle is very small. These reactions do not need any antibiotics in the first 72 hours.
  • If the swelling progresses rapidly, is associated with breathing problems, or makes you very concerned about an allergic reaction, seek urgent medical attention and/or call 9-1-1.

No. “Long COVID” symptoms are caused by the virus, and the vaccines do not contain any virus. Side effects from the vaccine are common and should resolve within a few days.

• Since the vaccines are new, studies are ongoing to determine how long the immunity lasts or if there are long-term side effects. The long-term data we’re still waiting for is more about long-term efficacy (how long immunity lasts) than long-term safety.
• It is very unlikely for long-term effects to develop, as these initial vaccines are not live vaccines and side effects most often present in the first few days after vaccination.

Polyethylene glycol (PEG) allergies are rare. PEG is a common ingredient found in many products, and most people use these products without having any allergic reactions.

If you have used any of the following medications without allergies, you are not allergic to PEG:

• Extra Strength Tylenol, Tylenol EZ tabs, Tylenol Gel Caps
• Advil Liqui-Gels
• Benadryl 25 or 50mg pink caplets
• Laxaday
• Go-Lytely
• Reactine 5 or 10mg tablets
• Enteric coated daily low dose aspirin (81 mg)

To identify PEG on a label, look for:

• “Polyethylene glycol”
• PEG followed by a number (PEG-40).
• PEG followed by a number and then another ingredient name (PEG-20 cocamine)
• Complex PEG compounds with many slashes, but will always contain “PEG” (BIS-PEG/PPG-16/16 PEG/PPG-16/16 Dimethicone)

• No. They do not contain mercury, formaldehyde, aluminum, or fetal cells.
• On this site you can review a list and explanation of:
  •  Pfizer-BioNTech vaccine ingredients
  •  Moderna vaccine ingredients
  • Oxford-AstraZeneca vaccine ingredients
  • Janssen (Johnson & Johnson) vaccine ingredients

It’s natural to question the motive as to reasons why Indigenous Peoples are identified as a priority.

Along with healthcare workers and residents of long-term care/retirement homes, Indigenous Peoples have been identified as a priority population because evidence shows they are among those at greatest risk of serious, life-threatening implications if they contract COVID-19.

Moreover, chronic medical conditions with a greater prevalence among Indigenous Peoples such as respiratory disease, heart disease, diabetes, kidney and liver disease, have been found to be at greater risk of more severe outcomes from COVID-19 (IPHCC, 2021).

The Canadian and provincial governments are monitoring cases of new COVID-19 variants in Canada.

Early data suggests that these variants may be more easily transmitted and may impact the severity of disease. There is some evidence to suggest that some variants of COVID-19 may have an impact on the efficacy of approved COVID-19 vaccines. However, real world studies so far have shown that the approved vaccines are effective against the variants present in Canada.

Additional research is ongoing to learn more about these variants.

It is normal for viruses to change and develop different versions (variants), and there is a risk that certain changes may make COVID-19 more resistant to vaccines. For example, early evidence suggests that vaccines may not be as good at protecting people from the variant originating in South Africa.

Luckily, vaccine companies are doing research to update their vaccines to better protect against variants of concern. The best way you can help reduce the spread of COVID-19 variants is to continue to follow public health guidelines.

Efficacy means how well the vaccine works in clinical trials. An efficacy of 95% means that in clinical trials, the vaccine decreased the number of COVID-19 cases by 95% compared to the population that received the placebo injection.

But clinical trials are not real-world conditions. For example, people in clinical trials are generally healthy, because researchers do not want to include people who are sick or are taking certain medications.

Effectiveness means how well the vaccine protects in the real world. Because effectiveness includes less healthy people, it is usually lower than efficacy. An effectiveness of 95% means that in the real world, the vaccine decreased the number of COVID-19 cases by 95% compared to what we would expect in people who are not vaccinated.

Information so far suggests that the approved vaccines are very effective in the real world. Clinical trials already showed that all 4 approved vaccines have high efficacy.

No. Vaccinated individuals can still be infected, but vaccination greatly reduces the risk of infection, and reduces the risk of an infection progressing to the more severe form of the disease.

When an individual tests positive for COVID-19 14 days or more after the second dose of a 2-dose COVID-19 vaccine series, this is known as a breakthrough infection. In Ontario, the rate of breakthrough infections among fully vaccinated individuals has been very low.

In the period of December 14, 2020 – August 21, 2021, Public Health Ontario found that (PHO, August 31, 2021):

• 94.8% of COVID-19 cases were among unvaccinated individuals. 92.4% of hospitalizations and 92.1% of deaths occurred among unvaccinated individuals.
• 0.9% of cases were breakthrough cases among vaccinated individuals. Breakthrough cases accounted for 0.9% of hospitalizations and 1.3% of deaths.

No. An effectiveness of 95% means that the vaccine decreased the number of COVID-19 cases by 95% compared to the population that received the placebo injection. While it is still possible for vaccinated people to get COVID-19, an effectivess of 95% does not mean that 5% of vaccinated people will still get the virus

• The AstraZeneca clinical trials show protection starts from approximately 3 weeks after receiving the first dose and persists up to 12 weeks. A second dose should be given at a 4-to-12-week interval after the first dose, with evidence that suggests the vaccine increases effectiveness with longer intervals between doses.
• Pfizer-BioNTech’s clinical trials show that individuals may not be optimally protected until at least 7 days after their second dose of vaccine, given 21 days after the first dose.
• Moderna’s clinical trials show that individuals may not be optimally protected until after receiving the second dose of the vaccine, given 28 days after the first dose.

References

• Product monograph, including patient medication information: Pfizer-BioNTech COVID-19 vaccine, February 8, 2021
• Moderna Covid-19 Vaccine Product Monograph, February 19, 2021
• AstraZeneca COVID-19 Vaccine Product Monograph, March 24, 2021

When scientists measure efficacy and effectiveness, they focus on symptomatic COVID-19 cases. So even with a highly effective vaccine, it is possible for people to develop infections without symptoms. These asymptomatic people can spread COVID-19 to others close to them. Preventing symptomatic cases helps, but in order to better protect against transmission, vaccines must also be able to prevent asymptomatic COVID-19 infections.

Scientists are researching how well the COVID-19 vaccines prevent these asymptomatic cases and how well they prevent transmission. The information we have so far suggests that the Pfizer-BioNTech and Oxford-AstraZeneca vaccines do this well (Preprints with The Lancet, February 1, 2021; Authorea Preprint, February 24, 2021).

The information we have so far suggests that the approved vaccines do this well.

Though we are still learning how many people have to be vaccinated against COVID-19 before most people can be considered protected, it’s currently estimated that 40% – 90% vaccination coverage is required to achieve herd immunity for COVID-19.

References

• Key Things to Know About COVID-19 Vaccines (CDC, March 8, 2021)
• COVID-19 – What We Know So Far About… Herd Immunity (Public Health Ontario, January 15, 2021)