Fitness basics
Learning Center
COVID-19 variants: What's the concern?
The virus that causes COVID-19 has changed over time, which has affected prevention, diagnosis and treatment of COVID-19.
COVID-19 vs. flu: Similarities and differences
Find out the similarities and differences between coronavirus disease 2019 (COVID-19) and the flu (influenza) and learn about ways to prevent getting these diseases.
COVID-19, cold, allergies and the flu: What are the differences?
Knowing if you have COVID-19, a cold, the flu or seasonal allergies isn't easy. Find out about the differences between these illnesses.
COVID-19: Long-term effects
Learn about the possible long-term effects of COVID-19.
COVID-19: Who's at higher risk of serious symptoms?
Advanced age and some health conditions can raise the risk of serious COVID-19 (coronavirus disease 2019) illness.
Calcium supplements: A risk factor for heart attack?
Learn about the possible link between calcium supplements and heart attacks.
Can vitamin D protect against coronavirus disease 2019 (COVID-19)?
Find out what the research says about links between this key vitamin and the widespread viral infection.
Canker sore
Canker sore — Learn about the causes, treatment and prevention of this painful mouth sore.
Cataract surgery
Cataract surgery — Overview covers risks, complications, results of this eye surgery.
Cataracts
Are things starting to look fuzzy or blurry? Find out about symptoms, diagnosis and treatment for this common eye condition.
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