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OHS and CanPath COVID-19 Antibody Study

The OHS asked a subset of around 12,000 participants who completed the COVID-19 Questionnaire to also provide a small blood spot sample, which was analyzed to detect antibodies to SARS-CoV-2, the virus that causes COVID-19. Please read these FAQs to learn more about the initiative:

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About the COVID-19 Antibody Study

What are the OHS and CanPath COVID-19 research initiatives?

  • COVID-19 Questionnaire administered in 2020 across the CanPath cohort of 330,000 participants
  • CIHR and CITF-funded seroprevalence study of 3,000 randomly selected participants
  • CITF-funded seroprevalence study of 20,000 participants in populations at high risk of exposure to COVID-19

Who conducted the COVID-19 Antibody Study?

The Ontario Health Study is part of the Canadian Partnership for Tomorrow’s Health (CanPath), which received funding from the COVID-19 Immunity Task Force and the Canadian Institutes of Health Research to collect information related to COVID-19 immunization. CanPath cohorts that participated in this initiative include the OHS, as well as Atlantic PATH, CARTaGENE (Quebec), the Manitoba Tomorrow Project, Alberta’s Tomorrow Project, and the BC Generations Project.

The data we collected will be shared with researchers across Canada and internationally to investigate COVID-19 infection rates in the Canadian population, to understand the science behind COVID-19 immunity, and to study health related outcomes.

When was this study conducted?

Blood spot sample collection began in March of 2021. For those selected to take part in the longitudinal study, a second and third blood spot sample were collected 6 and 12 months after the first sample. The collection of these additional samples was completed in January of 2023.

Didn’t I complete a CanPath COVID-19 study in 2020?

Yes. Almost 100,000 CanPath and regional cohort participants completed the CanPath COVID-19 Questionnaire. The information collected by that questionnaire is providing researchers and public health professionals with great insights into how the pandemic has affected the health and well-being of Canadians. This will help them understand how best to respond to the current COVID-19 pandemic as it evolves, and will also inform future pandemic responses.

In 2021 and 2022, CanPath and its regional cohorts conducted a COVID-19 serology study to see which Canadians had developed antibodies to the SARS-CoV-2 virus, the virus that causes COVID-19. This study captured important data that will support researchers who are working on projects related to the COVID-19 pandemic.

This study built on the information already captured by the previous COVID-19 questionnaire, including potential sources of exposure to the virus, such as those experienced by volunteers and frontline workers.

About antibody testing

What is a blood spot sample?

A blood spot sample is a process where a few drops of blood are collected on a piece of filter paper and dried. In this study, blood will be collected through a finger prick.

What is serology or antibody testing?

Serological tests do not detect the SARS-CoV-2 virus (the virus that causes COVID-19) itself. Instead, they detect the antibodies your immune system produces in response to an infection or after receiving a vaccine. Serology tests are also known as antibody tests.

The immune response to a virus involves the creation of different types of antibodies produced at different stages of an infection:

  1. Early antibodies, called IgM antibodies, provide the first indication of the body’s response to an infection. These antibodies are not as specific and generally are not as long lasting, so interpreting their significance requires clinical experience
  2. IgG antibodies are specific to a virus, such as the SARS-CoV-2 virus. Early research results suggest these antibodies can be reliably detected 14 days after a person is infected with COVID-19 or receives a COVID-19 vaccine.

The OHS and CanPath tested dried blood spots sampled from participants for IgG antibodies that are specific to SARS-CoV-2, the virus that causes COVID-19.

The relationship between antibodies and immunity to infection with SARS-CoV-2 is still not fully understood and continues to evolve rapidly.

Antibodies are present for an undetermined period of time after an infection has ended, or after a person has been vaccinated.

Serological studies, such as this one, aim to investigate these unknowns to provide a better understanding of COVID-19 and to identify how Canadians and public health officials can best respond to and manage the threat of the virus within our population.

How was my blood sample processed?

A lab in Toronto analyzed your blood spot sample to determine if there were COVID-19 antibodies in your blood. For a small subset of samples, a lab in Ottawa also analyzed the sample to look at neutralizing antibody levels. This analysis looks for antibodies that can bind to a virus and interfere with its ability to infect a cell. Once the lab analyses were completed, your sample was returned for secure storage at the Ontario Health Study. Your sample may be used in the future by approved researchers for further health research, just like the biological samples some participants provided upon joining the OHS.

How is my privacy protected?

Your data will be protected using current security safeguards. These safeguards include keeping your personal information separate from study data, assigning a unique code number to identifying information, and only releasing coded data to approved researchers. 

Vaccines and the COVID-19 Antibody Study

Can the test detect antibodies from a COVID-19 vaccine? Can the test differentiate between antibodies from a COVID-19 exposure compared to antibodies from the vaccine? 

The lab tests we conducted were able to detect antibodies developed after receiving a COVID-19 vaccine. The results that participants received do not differentiate between antibodies resulting from a COVID-19 infection or a COVID-19 vaccine. Information about antibodies and the COVID-19 vaccine is evolving quickly. This study aims to help answer questions about COVID-19 antibodies and immunity.

If I have been vaccinated for COVID-19 but my sample tests negative for antibodies, does this mean my vaccine did not work?

If you have received a COVID-19 vaccine but received a negative test result, antibodies may not have been present in the sample you provided to us. For example, if you received a vaccine, then provided a blood spot sample shortly thereafter, the antibodies would not have had time to develop by the time the lab tested your sample.

Receiving your results

Will I get the results of the antibody testing?

Yes, you will get an email when your results are available to view online. It will take up to three months to receive the test results.

You will receive one of four possible results: a positive result confirming that there are COVID-19 antibodies in your blood, a negative result indicating that there are no COVID-19 antibodies in your blood, an inconclusive result indicating that there are some COVID-19 antibodies in your blood but not enough to meet the threshold for a positive result, or a technical failure result stating that an error occurred with the sample or analysis and the lab could not determine if COVID-19 antibodies were present.

The antibodies being tested for in this study become detectable approximately 10 to 14 days following infection or vaccination. Please consult your regular health practitioner if you have any questions about the findings from your blood spot sample.

What do my antibody test results mean?

The CanPath lab tests detect the presence of three antibodies against:

  • the spike protein which sits on the SARS-CoV-viral envelope (SmT1)
  • the receptor binding protein (RBD)
  • the SARS-CoV inner nucleocapsid protein (NP)

Antibodies to the spike (SmT1) and receptor binding domain (RBD) represent response to either prior infection or vaccine. Antibodies to the nucleocapsid proteins (NP) represent response to prior infection.

The lab set a threshold for positivity for each protein. A participant’s antibody test result is based on the combined result from the three tests. The lab labels a sample as ‘positive’ based on it passing a set cut-off value on 2 of 3 antibodies. It labels a sample as ‘negative’ or ‘Inconclusive’ when results come in below the lab’s set threshold for a positive result. A ‘technical failure’ result indicates that an error occurred with the sample or analysis and the lab could not determine if COVID-19 antibodies were present.

For privacy reasons, OHS staff do not have access to individual participant results.

Early findings presented in May 2023 found that 53% of COVID-19 diagnoses were among those who neither knew, nor suspected, they had been infected! Read more about these findings here. 

When can I expect to receive the results of the antibody test of my blood spot sample?

Study participants will receive an email when the results of their blood spot sample are available to view online via their OHS account, approximately three months after providing their sample.

Who will see the results of my blood spot sample?

The results of the serological (antibody) test obtained from your blood spot sample and any additional health measurements will be stored in the OHS database and in the CanPath national database. Your personally identifying information is only accessible to a small number of OHS staff.

Coded and de-identified questionnaire data and antibody test results will also be shared with the federal COVID-19 Immunity Task Force (CITF), which funded the study. A copy of your questionnaire and the test results from your blood spot sample will be stored in a database at McGill University. Only the information and test results collected as part of this study will be part of the CITF database. No other information you have provided to the OHS will be part of this database, and the CITF will not be able to link your data to you as an individual.

If I am notified that my sample tests positive for antibodies, how long will these antibodies last?

This is still unknown. Your participation in this study is important so we can learn more about COVID-19 infections, antibodies and immunity.

If my sample tests positive for COVID-19 antibodies, do I need to self-isolate or get tested for COVID-19?

No. Antibodies are not an indication of a current COVID-19 infection. If your sample tests positive for COVID-19 antibodies, this indicates that you have been infected with COVID-19 at some point in the past, or could be the result of a COVID-19 vaccine. If you are having COVID-19 symptoms unexplained by other health conditions, please follow up with your health practitioner, or contact Telehealth Ontario.

If I am notified that my sample tests positive for antibodies, does this mean I no longer need to practice protective measures (i.e. physical distancing, hand-washing, masking)?

At this time, it is unknown how long antibodies to COVID-19 may last. It is therefore important that you continue to follow local public health guidelines.

Will the antibody test detect antibodies from the variants of COVID-19?

Yes. The lab conducting our antibody testing continues to keep an eye on the new variants detected and will adapt the test as needed to capture antibodies from variants of the virus. The results you receive will not differentiate between antibodies resulting from a COVID-19 infection or a COVID-19 vaccine, nor will it specify which variant.

What were the results of the COVID-19 Antibody Study?

Some surprising findings were generated from a national COVID-19 Antibody Study that included almost 10,000 OHS participants. Among them:

  • Just over half of the COVID-19 diagnoses (53%) were among those who neither knew, nor suspected, that they had been infected
  • During the highly-infectious Omicron phase in 2022, vaccination (at least 2 doses) or a booster shot provided protection from infection for 4 months
  • However, getting infected with the virus conferred protection against re-infection for a full 8 months
  • Long-COVID affected 6% of study participants, while 60% of those who experienced symptoms saw their condition resolved in under 2 weeks.
  • At every dose (up to 6), the risk of infection was lower among participants who got a Moderna shot as their most recent vaccine brand received, compared to a Pfizer shot; a 14% lower risk, on average
  • Over 2 million lines of data were analyzed for the study. This is because the statistical model included several time-varying covariates, including vaccination number, vaccine brand most recently received, bivalent vaccine status, and cumulative number of SARS-CoV-2 positive tests.

These results were presented May 30, 2023 by OHS Scientific Associate, Dr. Victoria Kirsh in a webinar for CanPath, a national health research platform for which the OHS is the largest contributor.

You can view the full presentation here: https://canpath.ca/2023/04/hybrid-event-covid-19-vaccine-effectiveness-support-canada-study/