What is the prevalence of long COVIDs? What are the differences between studies?

Kathleen Kinder
Kathleen Kinder

Updated · Jun 22, 2022


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Ziyad Al Aly is a clinical epidemiologist with access to electronic medical records provided by the US Department of Veterans Affairs for military veterans. Al-Aly (based in VA St. Louis Healthcare System, Missouri, Missouri) has been studying the long-term implications of COVID-19 with his colleagues. These effects include diabetes and cardiovascular disease. The researchers also addressed long COVID.

It is a condition where people experience symptoms that persist for several months after a SARS-CoV-2 acute virus infection. Recent findings by the researchers were surprised. They found that COVID is a long-term condition caused by long-term illness, and only 15% of those who have had previous vaccinations are at risk. This is significantly less than other estimates4 and indicates that vaccines reduce half of the risk.

This whiplash result is something that people who have long-COVID research are used to. Numerous studies show inconsistent results. Policymakers and the public have different answers to fundamental questions due to differences between data types and analyses. Is long COVID a common term? What impact does vaccination, reinfection, or the latest SARS/CoV-2 variants have on your future risk of developing this condition?

The answers to these questions are useful for COVID-19 policy development. However, confusion can result from the continuous drip of seesawing research. Al-Aly says. Al-Aly stated that uncertainty can lead to trustlessness, which is problematic.


One problem is the COVID extended definition. This is associated with over 200 symptoms. These symptoms can be severe and very annoying. These symptoms can last several months to years, and they have a distressing tendency, even months, to return after apparent recovery.

Long COVID was not defined or diagnosed by a consensus. Patients and researchers are disappointed by the World Health Organization’s attempts to reach an agreement in 2021. But studies continue to use different criteria in determining the condition. The prevalence rate of this condition can vary between 5 and 50%.

Complex conditions require that we recognize the various symptoms and possible effects of individual characteristics. For example, age and severity of acute SARS-CoV-2 virus infections. Al-Aly’s analyses have many advantages. Data from large healthcare systems can offer substantial sample sizes. Al-Aly studied long COVID among patients infected with a breakthrough strain of the virus. This is after vaccination. The study included records from 13 million people. Al-Aly stated that although 91% of the participants were men the analysis still contained 1.3 million women. This figure is significantly higher than in most other studies.

Big-number benefits

Researchers can perform complex statistical analyses using large numbers of data from health records in order to closely match the demographics of coronavirus-infected patients to those without the virus. Theo Vos works as an epidemiologist for The Institute for Health Metrics and Evaluation in Seattle. He has used multiple data sources to study COVID over a long period.

There are, however, some drawbacks. Walid Gellad from Pennsylvania, who is a physician studying health policy at the University of Pittsburgh, says people mistakenly think that the size of a research study correlates with its validity or quality.

Coding lessons

Another issue is how symptoms and conditions are recorded in claims and electronic medical records. Vos notes that although doctors may record codes for many diseases and symptoms, they don’t always list everyone. Vos adds that codes can also be used to identify specific conditions. Vos points out that each doctor might have a different choice. This could result in COVID reporting times and lengths being other. Gellad states that electronic health records are instrumental and have valuable information. They are not the best at answering the question of “how common is something?”

Some methods have their flaws, too. Some studies rely upon self-reporting. This is the case with the COVID-Symptom Study app from King’s College London. Data from the app showed that vaccination reduces people’s chances of suffering COVID for over 28 days or more after an acute infection by half. Gellad says that studies, where participants self-report symptoms can be biased as people with symptoms are more likely not to participate. Studies that rely on smartphone apps might not be able to capture the full data of disadvantaged communities.

Searching for a common thread

Alwan has been a long-standing advocate for COVID and collecting data about the condition. He praises the ONS study design. This involved enrolling a group with careful attention to represent the UK population, then following up to inquire about their symptoms and infection status.

Alwan also says that other aspects such as whether the control is used can impact the results. However, research should not be stopped just because of different definitions and methods. She said, “That’s nothing new.” “It’s something we had before COVID, for different conditions.”

Al-Aly believes that discrepancies between study results are not surprising or alarming. Al-Aly says epidemiologists often use multiple data sources and analysis methods to combine evidence. Although it may not be possible to quantify the vaccine’s impact on long-term COVID risks accurately, researchers can still look for trends. Al-Aly explains, “You search for the common theme.” “Vaccines are better than no vaccines” is the common thread.

Kathleen Kinder

Kathleen Kinder

With over 4 years of experience in the research industry, Kathleen is generally engrossed in market consulting projects, catering primarily to domains such as ICT, Health & Pharma, and packaging. She is highly proficient in managing both B2C and B2B projects, with an emphasis on consumer preference analysis, key executive interviews, etc. When Kathleen isn’t deconstructing market performance trajectories, she can be found hanging out with her pet cat ‘Sniffles’.