Adults who reported having COVID-19 at least twice had 76% higher odds of being diagnosed with a new health condition than those who reported never being infected, according to a Canadian government study summarized by CIDRAP.
The research, by the Public Health Agency of Canada and Statistics Canada, was published in the Canada Communicable Disease Report. It shows an association, not proof that reinfection caused the new conditions.
The timing matters for U.S. households heading into fall. As of Sept. 11, the CDC said COVID-19 activity was elevated and increasing nationally, although hospitalizations remained low. With schools back in session and many adults already infected more than once, questions about the long-term effects of repeat infections are practical ones.
Reading the 76% Figure Carefully
Researchers analyzed data collected from April 2022 to June 2023 from nearly 9,000 respondents to the Canadian COVID-19 Antibody and Health Survey and its follow-up questionnaire. Participants reported how many confirmed or suspected infections they had and whether they were diagnosed with any of 21 conditions after their first infection. These included respiratory, cardiovascular, neurologic, and musculoskeletal disorders, as well as diabetes, cancer, sleep apnea, mental illness, and chronic fatigue syndrome or fibromyalgia.
About 47% reported one infection, and about 20% reported two or more. Overall, 11% reported a new condition during the study period.
Compared with people reporting no infection, those reporting two or more had an adjusted odds ratio of 1.76. Odds ratios compare the likelihood of an outcome between groups. The figure does not mean that 76% of people with repeat infections developed a new illness.
Repeat infections were also tied to about five times the odds of a respiratory diagnosis and nearly four times the odds of back problems. Those estimates had wide confidence intervals, meaning they are less certain.
The conditions covered a wide range, and the published summary does not describe how severe they were or whether they lasted. A new back problem carries very different implications than a new heart condition.
Symptoms mattered too. People whose first infection caused symptoms that interfered with daily activities had 63% higher odds of a new diagnosis, and those with symptoms lasting three months or more had more than three times the odds.
Evidence Gaps and Independent Context
The authors list several limits. Infection counts and health information were self-reported, so some people may have misremembered details. Some who reported no infection may have had silent or undiagnosed COVID-19. People with severe or lingering symptoms may also have seen clinicians more often, creating more chances for unrelated conditions to be found.
Even so, the researchers wrote that the findings “reinforce the continued importance of public health efforts to prevent infection.”
Earlier U.S. research points in a similar direction with a different design. A 2022 analysis of Department of Veterans Affairs health records, led by Dr. Ziyad Al-Aly of Washington University in St. Louis and published in Nature Medicine, found that reinfection was linked to added risks of death, hospitalization, and problems affecting the lungs, heart, and other organs. That study mostly involved older white men, which limits how widely its results apply.
A separate review summarized by CIDRAP found that symptoms lasting three months or more are also common after other respiratory infections such as flu and RSV, suggesting lingering post-viral illness is not unique to COVID-19.
The findings come from Canada, where testing practices and health care access differ from those in the U.S., so results here could differ.
MedicalDaily Evidence Check: This was an observational survey of about 9,000 Canadian adults. It found an association between repeat infection and new diagnoses. It did not prove cause and effect, and it has not changed U.S. clinical guidance.
Reducing Reinfection Risk This Season
People at higher risk of severe COVID-19 include adults 65 and older, people with chronic heart, lung, or kidney disease, and those with weakened immune systems. People who had lingering symptoms after earlier infections may also want to take extra care. CDC scenario modeling had projected summer increases in the South and West, regions that did not see substantial COVID-19 activity last winter.
Parents may wonder whether every infection carries lasting harm. This study cannot answer that for children because it included only adults. Families can focus on proven basics, such as keeping sick children home and protecting relatives with chronic illness. Workers without paid sick leave face harder choices, and some local health departments offer free testing or vaccination clinics.
Check your local trend on the CDC’s wastewater dashboard, which can provide an early signal of changes in infection levels. Ask a clinician or pharmacist whether a current COVID-19 vaccine is right for you and your family, since recommendations and insurance coverage may differ by age and health status.
Test when symptoms appear, stay home when sick, and consider a well-fitting mask in crowded indoor spaces when levels are high. The CDC’s prevention guidance also covers cleaner air and hand hygiene. People at higher risk should ask early about antiviral treatment, which works best when started soon after symptoms begin.
Contact a clinician if fatigue, shortness of breath, heart palpitations, or trouble concentrating persists for weeks after an infection. Seek emergency care for chest pain, severe breathing trouble, confusion, or bluish lips.
The authors called for more research on the long-term effects of reinfection and on the biological, behavioral, and systemic factors that may explain the link. MedicalDaily will follow new data as the fall respiratory season develops.
Key Questions Answered
What did the study find? Canadian adults who reported two or more COVID-19 infections had 76% higher odds of a new diagnosis than those who reported none.
Does reinfection cause new diseases? The study cannot prove that. It shows an association based on self-reported data.
Which conditions were most strongly linked? Respiratory conditions and back problems, though those estimates were less certain.
Is COVID-19 rising in the U.S.? As of Sept. 11, the CDC said activity was elevated and increasing nationally, with hospitalizations still low.
Who should be most careful? Older adults, people with chronic illnesses or weakened immune systems, and those who have had lingering symptoms.
How can I lower my risk? Ask about vaccination, test when sick, stay home when ill, improve ventilation, and consider a mask in crowded places.
When should I see a doctor? If symptoms last for weeks after infection, or right away for chest pain, severe breathing trouble, or confusion.