COVID-19

Key takeaways

• Stay home and away from others: until symptoms are improving and you have had no fever for 24 hours without fever-reducing medicine
• For the next 5 days: take extra precautions: a mask, distance, hand washing and cleaner air
• Most useful single change: Keep a few FDA-authorized home tests on hand and check their expiration dates.
• Commonest mistake: Going to work, school or gatherings while you still have a fever.
• See a doctor if any of the signs under "When to get help" below apply to you.

Why it matters

It still causes many hospital stays each year, mostly among older adults and people with chronic conditions or weakened immune systems, and treatment works best when started early.

The numbers, in one place

Published figures for COVID-19

Measure	Figure
Stay home and away from others	until symptoms are improving and you have had no fever for 24 hours without fever-reducing medicine
For the next 5 days	take extra precautions: a mask, distance, hand washing and cleaner air
Negative home antigen test with symptoms	test again 48 hours later
Antiviral treatment	for people at higher risk; works best started within 5 days of symptoms
Vaccine	updated each season; ask your doctor or pharmacist what is recommended for you

What helps

• Keep a few FDA-authorized home tests on hand and check their expiration dates
• Contact your doctor, a pharmacy or a telehealth service quickly after a positive test if you are 65 or older or have a chronic condition
• Rest, drink fluids and use acetaminophen (Tylenol) or ibuprofen for fever and aches as the label directs
• Open windows or use a portable HEPA air cleaner when someone at home is sick

What to avoid

• Going to work, school or gatherings while you still have a fever
• Asking for antibiotics, which do not work against viruses
• Visiting older relatives or someone with a weakened immune system while you are sick

In depth

SARS-CoV-2 spreads mainly through the air, in droplets and smaller particles released when an infected person breathes, talks, coughs or sings. Indoor spaces with poor ventilation let those particles build up, which is why cleaner air, distance and masks all reduce spread. People can pass the virus on a day or two before they feel sick, and they are most contagious in the first few days of symptoms.

The virus first infects cells lining the nose and throat. In most people the immune system contains it there, producing a cold- or flu-like illness. In some, especially older adults and people with weakened immunity or chronic disease, the infection reaches the lungs and triggers inflammation that can cause pneumonia, low oxygen levels and strain on the heart, kidneys and blood clotting. This is the stage antivirals aim to prevent.

The virus keeps changing, producing new variants that can partly escape the protection left by earlier infection or vaccination. That is why vaccines are updated and why protection fades over time. COVID-19 can also leave some people with symptoms that last for months, called Long COVID, which can follow even a mild initial illness.

Signs and symptoms

• Fever or chills, cough, sore throat and congestion or runny nose
• Tiredness, muscle or body aches and headache
• New loss of taste or smell, which is less common with recent variants
• Shortness of breath or difficulty breathing
• Nausea, vomiting or diarrhea
• Symptoms lasting weeks or months after infection, such as fatigue, brain fog or shortness of breath with activity

Causes and risk factors

• Close contact with an infected person, especially indoors
• Crowded or poorly ventilated spaces
• Age 65 or older, which sharply raises the risk of severe illness
• Chronic conditions such as heart or lung disease, diabetes, obesity or kidney disease
• A weakened immune system from illness or medicines
• Not being up to date on recommended vaccines

How it is checked

Home antigen tests detect viral proteins and give results in minutes. They are most reliable when you have symptoms and when repeated, because a single early test can miss an infection. PCR tests, done at clinics and pharmacies, detect the virus's genetic material and are more sensitive. Some clinics use combined tests that check for COVID-19 and flu at the same time.

If you are seriously ill, a doctor may check your oxygen level with a pulse oximeter, order a chest X-ray, and run blood tests to look for complications. A home pulse oximeter can be useful for some higher-risk people, but readings can be less accurate on darker skin, so symptoms such as breathlessness matter as much as the number.

Related topics

• Colds and Flu: What Published Guidance Supports (Immunity)
• The Evidence on Pneumonia, Without the Hype (Respiratory Health)
• The Evidence on Vaccination in Older Adults, Without the Hype (Healthy Aging)
• The Evidence on Adult Vaccination, Without the Hype (Preventive Care)

Where to go next

• What People Get Wrong About COVID-19
• COVID-19 for Beginners: Where to Start
• Infectious Diseases: The Complete Guide
• What the Guidance Really Says About Flu Versus a Cold
• Measles: What the Evidence Actually Says

When to get help

Contact your doctor if symptoms get worse after starting to improve, or if you are at higher risk and test positive. Call 911 for trouble breathing, persistent chest pain or pressure, new confusion, being unable to wake or stay awake, or pale, gray or blue-colored skin, lips or nail beds.

Where this comes from

• CDC — Respiratory Virus Guidance
• CDC — Treatment of Respiratory Illnesses
• FDA — At-Home COVID-19 Antigen Tests: Take Steps to Reduce Your Risk of False Negative Results

How this page was put together

Every figure, recommendation and warning above is taken from the guidance named in Where this comes from. Nothing on this page is inferred, summarized or generalized beyond what those bodies publish: where they give a number, it is their number, and where they are silent, so are we. Pages are rebuilt whenever the underlying record changes. Sign-off by a named clinician, where it has happened, is shown at the top of the page along with the date.

Medical disclaimer

This article is general information, not medical advice. It cannot account for your own history, medication or circumstances. Always speak to your doctor, pharmacist or another qualified health professional before making changes that affect your treatment, and never delay seeking medical advice because of something you have read here. In an emergency, call 911.