COVID-19
COVID-19 is an infectious disease caused by SARS-CoV-2 that can range from a mild respiratory illness to severe pneumonia, organ injury, long COVID, or death.
What COVID-19 is
COVID-19 is the disease caused by SARS-CoV-2. It was first identified in 2019 and became a global pandemic, but it now circulates alongside other respiratory viruses. Most infections are mild to moderate, yet COVID-19 can still cause severe illness, especially in people at higher risk.
How SARS-CoV-2 spreads
SARS-CoV-2 spreads mainly through respiratory particles. Risk is higher in crowded indoor spaces, poorly ventilated rooms, and close contact, especially when people are infectious before they know they are sick. Cleaner indoor air, distance, staying home when ill, and well-fitting masks in higher-risk settings can all reduce exposure.
Symptoms
Symptoms can include fever, chills, cough, sore throat, congestion, runny nose, shortness of breath, fatigue, headache, muscle aches, nausea, vomiting, diarrhea, and loss of taste or smell. Some people have no symptoms. Others worsen after several days, especially if oxygen levels drop or pneumonia develops.
Testing
Testing helps confirm infection, guide treatment decisions, and reduce spread to others. Antigen tests can give fast results and are useful when repeated according to instructions. Molecular tests are more sensitive and can be useful when a clear diagnosis is important. Timing matters because viral levels change during illness.
Who is at higher risk
Higher risk of severe COVID-19 is linked to older age, pregnancy, weakened immune systems, disability, and medical conditions such as chronic lung disease, heart disease, diabetes, kidney disease, cancer, and obesity. Risk also depends on vaccination status, prior infection history, access to care, and current variant patterns.
Treatment
Treatment depends on severity and risk. People at higher risk may benefit from antiviral treatment soon after symptoms start, so they should contact a clinician quickly after a positive test or suspected infection. Severe illness may require oxygen, hospital care, medicines that reduce harmful inflammation, or intensive support for breathing and organs.
Vaccines and changing variants
COVID-19 vaccines reduce the risk of severe illness, hospitalization, and death, though protection against infection can vary as immunity and variants change. Vaccine recommendations are updated over time, so people should follow current local guidance for their age, health conditions, pregnancy status, and immune status.
Long COVID
Some people develop long COVID, a group of symptoms or health problems that continue or appear after the acute infection. Symptoms can include fatigue, breathing problems, brain fog, sleep disruption, dizziness, pain, and worsening after exertion. Long COVID can follow mild or severe initial illness, and research is still evolving.
Why it matters
COVID-19 changed health care, work, schools, travel, surveillance, vaccine science, indoor-air awareness, and public trust. Even as emergency phases have ended in many places, the disease still matters because severe cases, outbreaks, long-term effects, and unequal access to prevention and treatment continue.
What public health teams watch
Public-health teams monitor hospitalizations, deaths, variants, wastewater signals, vaccine effectiveness, treatment resistance, outbreaks in high-risk settings, and health inequities. The goal is to keep guidance proportionate as the virus changes and as community risk rises or falls.