COVID-19 is a respiratory illness caused by a virus called SARS-CoV-2, a member of the coronavirus family. First identified in late 2019, it spread rapidly across the globe and was declared a pandemic in March 2020. The virus continues to circulate, producing new variants and causing illness that ranges from mild cold-like symptoms to severe pneumonia and, in some cases, death. Most people recover within a few weeks, but a significant minority develop lingering symptoms that last months.
How the Virus Infects Your Body
SARS-CoV-2 is an enveloped RNA virus, meaning its genetic material is a single strand of RNA wrapped in a fatty outer shell. Studded across that shell are club-shaped spike proteins that give coronaviruses their name: under a microscope, the spikes resemble the sun’s corona. These spike proteins are the virus’s key tool for breaking into your cells.
When you inhale viral particles, the spike protein latches onto a receptor called ACE2 on the surface of cells lining your airways. Think of it like a key fitting into a lock. Once attached, the spike protein changes shape, pulling the virus’s outer membrane flush against the cell membrane so the two fuse together. The virus then dumps its RNA inside the cell, hijacking the cell’s machinery to make copies of itself. Those copies burst out to infect neighboring cells, and the cycle repeats. Additional molecules on cell surfaces, including one called neuropilin-1, can assist the virus in attaching more efficiently. Neuropilin-1 also provides a possible route into the nervous system, which may help explain neurological symptoms like loss of smell and confusion.
Common Symptoms and Timeline
Symptoms typically appear 2 to 14 days after exposure. In clinical studies, the most frequently reported symptoms and their approximate prevalence are:
- Fever: ~94% of symptomatic patients
- Exhaustion: ~89%
- Cough: ~71%
- Loss of taste: ~64%
- Sore throat: ~64%
- Body aches: ~63%
- Loss of smell: ~50%
- Shortness of breath: ~44%
- Headache: ~35%
- Diarrhea: ~31%
Less common symptoms include confusion (about 20%), vomiting, skin rashes, and runny nose. A notable portion of infections produce no symptoms at all. The mix and severity of symptoms can vary by variant, vaccination status, and individual health. Mild cases often feel like a bad cold or flu and resolve within one to two weeks. Severe cases can involve pneumonia, dangerously low oxygen levels, and organ damage, particularly in older adults or people with underlying conditions like diabetes, heart disease, or compromised immune systems.
How COVID-19 Spreads
The virus spreads primarily through the air. When an infected person breathes, talks, coughs, or sneezes, they release tiny respiratory particles carrying the virus. Larger droplets tend to fall to the ground within a few feet, but smaller aerosol particles can linger in the air for minutes to hours, especially in poorly ventilated indoor spaces. This is why crowded, enclosed settings carry the highest transmission risk. Surface transmission (touching a contaminated object, then touching your face) is possible but plays a much smaller role than airborne spread.
Testing: Rapid vs. PCR
Two main types of tests detect active COVID-19 infection. PCR tests amplify the virus’s genetic material and are considered the gold standard. Rapid antigen tests detect viral proteins and deliver results in about 15 minutes, but they are less sensitive. CDC data from the 2022-2023 season found that rapid antigen tests caught only about 47% of infections confirmed by PCR. When tested on days a person had a fever, sensitivity jumped to 77%. On days with no symptoms, sensitivity dropped to just 18%.
In practical terms, a positive rapid test is reliable, but a negative one doesn’t rule out infection, especially if you have no symptoms yet. If you test negative but feel sick, testing again 24 to 48 hours later improves accuracy. PCR tests remain the most reliable option when a definitive answer matters.
Treatment Options
Antiviral treatments work best when started early, ideally within five days of symptom onset. The primary outpatient option is Paxlovid, a twice-daily oral pill taken for five days. It’s approved for adults and authorized for children 12 and older weighing at least 88 pounds. Paxlovid works by blocking an enzyme the virus needs to replicate, reducing the risk of hospitalization and severe illness in people at higher risk.
A second option, remdesivir, is given intravenously over three days and can be started within seven days of symptom onset. A third antiviral, molnupiravir, is a five-day oral course used when the other two treatments aren’t accessible or appropriate. For most healthy people with mild symptoms, rest, fluids, and over-the-counter fever reducers are sufficient. Antivirals are typically reserved for those at elevated risk of severe disease.
Long COVID
A subset of people develop persistent symptoms after their initial infection. The World Health Organization defines this post-COVID condition as symptoms that start within three months of the initial illness and last at least two months. Common long COVID symptoms include crushing fatigue, brain fog, shortness of breath, joint pain, and heart palpitations. The condition can occur after mild infections, not just severe ones, and it can significantly disrupt daily life and the ability to work. The likelihood of long COVID appears to decrease with vaccination and with each subsequent infection for some people, though it remains an ongoing concern.
Variants and Ongoing Evolution
SARS-CoV-2 mutates as it replicates, producing new variants over time. The WHO tracks these variants based on how much they’ve changed from earlier strains and whether those changes affect transmissibility, severity, or the ability to evade immune protection from vaccines or prior infection. As of early 2025, JN.1 was classified as a variant of interest. Several sublineages, including KP.3.1.1, XFG, and BA.3.2, are under monitoring. These carry clusters of mutations in the spike protein that could affect how well current vaccines and prior immunity neutralize the virus.
Each new wave of variants tends to partially escape existing immunity, which is why updated vaccine formulations are released periodically, similar to the annual flu shot. Staying current with recommended boosters provides the best protection against severe illness, even as the virus continues to change.