Millions of Americans have recovered from COVID-19 since last March, per the Centers for Disease Control and Prevention (CDC). But an untold number of those patients are still feeling the effects of the novel coronavirus weeks or months after first becoming ill, often known as post-COVID syndrome. Now, new research is offering the first large-scale insights into the long-term side effects of the virus. In an analysis of 2 million COVID-19 patients, the largest of its kind so far, the nonprofit organization FAIR Health revealed that 23.2% of patients—more than 450,000 people—who had contracted the coronavirus sought treatment for at least one “post-COVID condition” a month or more after their diagnosis. The most frequently reported symptoms across all ages were pain, breathing difficulties, hyperlipidemia (fatty blood), malaise and fatigue, and hypertension. Other common symptoms of long COVID include headaches, heart palpitations, lingering loss of smell or taste, brain fog, and depression or anxiety, according to the CDC.