For Participants
Blood Collection
Starting in 2025, the Study will seek around 3,000 OHS participants to provide a second blood sample. This will help researchers learn more about chronic diseases like cancer, heart disease, and diabetes. By studying these new samples along with earlier ones, and with survey data and other records, researchers can get a clearer picture of your health. Having multiple samples from the same person also helps in studying changes in the blood over time, including early signs of disease, called biomarkers.
The Study previously invited selected participants who were between the ages of 30-74 when they completed the OHS questionnaire to also provide a blood sample. By March 31st 2017, the OHS collected over 40,000 Blood samples, which enhanced the data already given by participants, and allowed participants to learn something that they did not know about their health.
On this page you will find information about:
What We Do With Your Blood Sample
Participants providing a second blood sample to the OHS will have 6 tubes (approximately 44mL or ~2.5 tablespoons) of blood taken from a vein in their arm.
Most of each blood sample will be frozen so that researchers can use some of it in the future. A portion of the blood will be used for immediate analysis. A report with up to 15 of the results from the immediate blood analysis will be shared with participants on their OHS account.
These analyses include:
- Glycosylated Hemoglobin (HbA1c) Analysis: This test measures the long-term level of sugar in your blood, and is used to detect and monitor cases of diabetes. This test will help health researchers study diabetes, heart disease and obesity.
- Complete Blood Count: This test analyzes the cells in your blood to look for anemia, infection and other diseases. This test gives a general indication of your health. (Click to see all individual results)
- White Blood Cell (WBC) Count: White blood cells make up part of the immune system and help the body fight infection and certain diseases.
- Neutrophil Count: The most common type of white blood cell.
- Lymphocyte Count: A type of white blood cell.
- Monocyte Count: The largest type of white blood cell.
- Eosinophil Count: A type of white blood cell.
- Red Blood Cell Count: Red blood cells carry oxygen throughout the body.
- Hemoglobin: A component of red blood cells, hemoglobin delivers oxygen from the lungs throughout the body.
- Hematocrit: Hematocrit is the amount of red blood cells in the blood.
- Mean Corpuscular Volume: A measurement of the average size of your red blood cells.
- Mean Corpuscular Hemoglobin: A measurement of the amount of hemoglobin in your red blood cells.
- Mean Corpuscular Hemoglobin Concentration: The average amount of hemoglobin in your red blood cells, relative to their volume.
- Platelet Count: Platelets form clots in the blood, which can stop or prevent bleeding.
- Red Cell Distribution Width Test: This test is used to help diagnose anemia, where red blood cells can’t carry enough oxygen.
- Basophil Count: Basophils defend against allergens, infections, blood clotting, and parasites.
- Reticulocyte Count: Reticulocytes are immature red blood cells and are found in your bone marrow.
Protecting Your Privacy
We know how important it is to keep information about your health private and confidential. When samples are processed and stored for future research, anything that personally identifies you, such as your name, will be removed and replaced with a unique code. This unique code will let us link you to the sample you have provided while allowing us to keep your identity confidential. Only a handful of staff at the Ontario Health Study have access to the electronic key that matches your unique code to your identity.
Your coded information is encrypted, or “scrambled,” before it is transferred to our data centre. Coded information is only transferred over secure connections similar to those used for online banking. These secure connections are very difficult for outsiders to breach. The coded information is then stored on encrypted servers (very large computers) in a locked room that very few people can access. We only unscramble the information after it has safely arrived on our servers. The information you provide related to your blood sample will be stored on a separate server from your questionnaire responses or anything that personally identifies you (e.g., name, address, OHIP number).
All blood test results are de-identified and stored on secure servers at the Ontario Health Study. Access to the data and samples is governed by strict guidelines that protect the confidentiality of participants:
- All health researchers using data from the Study must receive approval from a Research Ethics Board or similar committee before access is given.
- No information about you will be given to your employer, family members or insurance companies.
- All blood samples will be given a unique code and no personal information will be kept on tubes that store blood samples. Samples are processed at accredited laboratories and stored in repositories located in Canada.
The OHS asked a subset of approximately 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:
Click to jump to each topic:
- 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
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.
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.
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 was collected through a finger prick.
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:
- 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
- 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 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.
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 looked 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.
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.
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.
The results of the serological (antibody) test obtained from your blood spot sample and any additional health measurements are 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 were also 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 is also 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 is part of this database, and the CITF will not be able to link your data to you as an individual.
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/