COVID-19: Symptoms, Causes, Treatment & Prevention Guide

What Is COVID-19 and What Causes It?

COVID-19 (Coronavirus Disease 2019) is a respiratory illness caused by the SARS-CoV-2 virus. The disease was first identified in late 2019 and quickly spread worldwide, becoming a pandemic. COVID-19 primarily affects the respiratory system but can impact other organs including the heart, brain, and kidneys.

COVID-19 is caused by a type of coronavirus called SARS-CoV-2 (Severe Acute Respiratory Syndrome Coronavirus 2). Coronaviruses are a large family of viruses that can cause illnesses ranging from the common cold to more severe diseases. SARS-CoV-2 belongs to the same family as the viruses that caused the 2003 SARS outbreak and the Middle East Respiratory Syndrome (MERS).

The virus primarily spreads through respiratory droplets and aerosols when an infected person coughs, sneezes, talks, or breathes. These tiny particles can travel through the air and be inhaled by people nearby. The virus can also spread by touching contaminated surfaces and then touching the face, although this is less common than airborne transmission.

Since its emergence, SARS-CoV-2 has evolved into multiple variants, each with different characteristics regarding transmissibility and immune evasion. Notable variants have included Alpha, Beta, Delta, and Omicron, with Omicron and its subvariants becoming dominant worldwide. New variants continue to emerge as the virus mutates, which is why ongoing surveillance and updated vaccines are important.

How COVID-19 Affects the Body

When SARS-CoV-2 enters the body, it primarily targets cells in the respiratory tract, particularly those in the nose, throat, and lungs. The virus uses spike proteins on its surface to attach to ACE2 receptors on human cells, allowing it to enter and replicate. This process can trigger an inflammatory response as the immune system fights the infection.

In most cases, the immune system successfully contains the infection, resulting in mild to moderate symptoms. However, in some individuals—particularly those with risk factors—the immune response can become excessive, leading to severe inflammation, pneumonia, and acute respiratory distress syndrome (ARDS). This hyperinflammation can also affect other organs, potentially causing blood clots, heart problems, kidney damage, and neurological issues.

The severity of COVID-19 varies widely between individuals. While many experience symptoms similar to a common cold, others develop life-threatening complications. Understanding the factors that influence disease severity has been crucial for developing treatment strategies and identifying high-risk populations who benefit most from preventive measures and early intervention.

What Are the Main Symptoms of COVID-19?

The most common COVID-19 symptoms include fever, dry cough, fatigue, sore throat, runny nose, headache, and muscle aches. Some people experience loss of taste or smell (anosmia/ageusia), which can last for weeks. Symptoms typically appear 2-14 days after exposure, with an average incubation period of 5-6 days.

COVID-19 symptoms can range from barely noticeable to severe and life-threatening. The spectrum of illness is remarkably broad—some infected individuals never develop symptoms at all (asymptomatic infection), while others require intensive care. Understanding this symptom range is essential for recognizing when you might be infected and when to seek medical care.

Current variants of the virus tend to cause symptoms that more closely resemble the common cold compared to earlier variants. Many people experience upper respiratory symptoms like runny nose, sneezing, and sore throat as their primary complaints. This overlap with other respiratory viruses makes testing important for confirming diagnosis, especially for high-risk individuals who might benefit from antiviral treatment.

The severity and combination of symptoms often depend on factors including vaccination status, prior infection, age, and underlying health conditions. Vaccinated individuals who experience breakthrough infections typically have milder and shorter-lasting symptoms compared to unvaccinated individuals. This protection against severe disease is one of the primary benefits of COVID-19 vaccination.

Common COVID-19 Symptoms

• Fever or chills: Temperature above 38°C (100.4°F), often fluctuating throughout the day
• Cough: Usually dry, persistent cough that may worsen over several days
• Fatigue: Overwhelming tiredness that can persist for weeks after other symptoms resolve
• Sore throat: Pain or scratchiness in the throat, common with current variants
• Runny or stuffy nose: Nasal congestion and discharge, increasingly common
• Headache: Often described as dull, persistent pressure
• Muscle or body aches: General achiness, particularly in the back and limbs
• Loss of taste or smell: Partial or complete loss, may persist for weeks or months
• Shortness of breath: Difficulty breathing, especially with exertion
• Gastrointestinal symptoms: Nausea, vomiting, or diarrhea in some cases

Warning Signs of Severe COVID-19

While most COVID-19 cases are mild, certain symptoms indicate potentially serious disease requiring immediate medical attention. These warning signs suggest that the infection may be progressing to affect the lungs or other vital organs, and early intervention can be life-saving.

Symptoms in Children

Children generally experience milder COVID-19 compared to adults, and many infected children have minimal or no symptoms. When symptoms do occur, they often resemble a common cold with runny nose, cough, and mild fever. However, a small percentage of children can develop a serious inflammatory condition called Multisystem Inflammatory Syndrome in Children (MIS-C), typically 2-6 weeks after COVID-19 infection.

Parents should watch for signs of MIS-C, which include persistent fever, abdominal pain, vomiting, diarrhea, rash, red eyes, and lethargy. This condition requires immediate medical attention and hospitalization. Fortunately, MIS-C is rare and has become less common with widespread vaccination and natural immunity in the population.

How Does COVID-19 Spread?

COVID-19 spreads primarily through respiratory droplets and aerosols released when an infected person breathes, talks, coughs, or sneezes. Transmission is more likely indoors, in crowded spaces, and in poorly ventilated areas. The virus can also spread through surface contact, though this is less common than airborne transmission.

Understanding how COVID-19 spreads is essential for protecting yourself and others. The virus is highly contagious, particularly with current variants like Omicron and its subvariants. An infected person can transmit the virus to others even before developing symptoms, which is why the disease has spread so efficiently worldwide.

When an infected person exhales, they release tiny respiratory particles containing the virus. Larger droplets typically fall to the ground within seconds and travel only short distances (about 1-2 meters). However, smaller aerosol particles can remain suspended in the air for minutes to hours and travel much farther, especially in enclosed spaces. This is why ventilation and air filtration are important protective measures.

The amount of virus a person sheds peaks around symptom onset and in the first few days of illness. However, people can be infectious for 1-2 days before symptoms appear, making it possible to spread the virus before knowing you're infected. The infectious period typically lasts 5-10 days for most people, though immunocompromised individuals may shed virus for longer.

Factors That Increase Transmission Risk

• Close contact: Being within 2 meters of an infected person, especially for prolonged periods
• Indoor settings: Enclosed spaces with limited ventilation trap respiratory particles
• Crowded spaces: More people means more potential sources of infection
• Prolonged exposure: Longer contact increases the amount of virus inhaled
• Poor ventilation: Stagnant air allows aerosols to accumulate
• Activities that increase respiratory output: Singing, shouting, heavy breathing from exercise

How Long Is Someone Contagious?

The infectious period varies between individuals, but research has established general patterns. Most people become contagious 1-2 days before symptoms appear, which is why pre-symptomatic transmission has been a major driver of the pandemic. Viral shedding peaks around symptom onset or within the first 1-2 days of illness.

For most people with mild to moderate illness, infectiousness decreases significantly after 5 days and is generally considered low after 10 days from symptom onset. Current guidelines suggest that people can typically end isolation after 5 days if symptoms are improving and they've been fever-free for at least 24 hours without fever-reducing medication. Wearing a mask around others for an additional 5 days provides added protection.

Who Is at Higher Risk for Severe COVID-19?

People at higher risk for severe COVID-19 include those over 65 years old, unvaccinated individuals, people with weakened immune systems, and those with chronic conditions like heart disease, diabetes, obesity, chronic lung disease, and kidney disease. These groups should prioritize vaccination and may benefit from early antiviral treatment.

While COVID-19 can affect anyone, certain factors significantly increase the risk of developing severe illness, requiring hospitalization, or dying from the disease. Understanding these risk factors is important for identifying who should take extra precautions and who may benefit most from preventive measures and early treatment.

Age is one of the strongest predictors of COVID-19 severity. The risk of severe illness increases steadily with age, with people over 65 facing significantly higher risks. Those over 85 have the highest hospitalization and mortality rates. However, severe disease can occur at any age, particularly in people with multiple risk factors.

Vaccination status profoundly affects outcomes. Unvaccinated individuals are many times more likely to be hospitalized or die from COVID-19 compared to those who are up-to-date on vaccination. This protection against severe disease remains strong even as vaccine effectiveness against infection wanes over time and with new variants.

Medical Conditions That Increase Risk

How Is COVID-19 Diagnosed?

COVID-19 is diagnosed through viral testing, primarily PCR tests (most accurate) or rapid antigen tests (convenient but less sensitive). PCR tests detect viral genetic material and can identify infections even with low viral loads. Rapid antigen tests are useful for detecting infection when viral levels are high, typically during peak contagiousness.

Accurate diagnosis of COVID-19 is important for several reasons: it guides treatment decisions, helps prevent spread to others, and enables public health monitoring. While symptoms can suggest COVID-19, many other respiratory viruses cause similar illness, making laboratory testing essential for confirmation.

The choice of test depends on the clinical situation, availability, and purpose of testing. For most people, rapid antigen tests performed at home provide a convenient way to check for infection. However, these tests may miss early infection or cases with lower viral loads. If you have symptoms and test negative with a rapid test, consider repeating the test in 24-48 hours or getting a PCR test for more definitive results.

Testing is particularly important for people at high risk for severe disease, as a positive result may make them eligible for antiviral treatment. Early treatment with medications like Paxlovid works best when started within 5 days of symptom onset, making timely testing crucial for those who might benefit.

Types of COVID-19 Tests

Monitoring Oxygen Levels at Home

A pulse oximeter is a small device that clips onto your finger and measures blood oxygen saturation. Normal oxygen saturation is 95-100%. Levels below 94% are concerning and warrant medical evaluation. For people recovering from COVID-19 at home, especially those at higher risk, monitoring oxygen levels can help identify respiratory deterioration before symptoms become severe.

How Is COVID-19 Treated?

Most mild COVID-19 cases require only supportive care: rest, fluids, and medications like paracetamol/acetaminophen for fever and pain. For high-risk individuals, antiviral medications (Paxlovid, molnupiravir) can reduce severity if started within 5 days of symptoms. Severe cases may require hospitalization, oxygen therapy, and corticosteroids like dexamethasone.

Treatment for COVID-19 depends on disease severity and individual risk factors. The vast majority of infections are mild and can be managed at home with supportive care. However, effective medications are now available that can prevent mild illness from progressing to severe disease in high-risk individuals, making early recognition and treatment important.

For mild cases, the focus is on symptom relief and preventing transmission to others. Rest is essential for recovery—your body needs energy to fight the infection. Staying well-hydrated helps thin mucus secretions and prevents dehydration from fever. Over-the-counter medications can manage specific symptoms: paracetamol (acetaminophen) or ibuprofen for fever and pain, and cough suppressants or throat lozenges for respiratory symptoms.

The development of effective antiviral treatments has been a major advance in COVID-19 management. These medications work by interfering with the virus's ability to replicate, reducing viral load and giving the immune system an advantage. However, they work best when started early in the infection, ideally within 5 days of symptom onset, which is why prompt testing is important for high-risk individuals.

Home Care for Mild COVID-19

• Rest: Allow your body to focus energy on fighting the infection
• Stay hydrated: Drink water, clear broths, and electrolyte drinks; aim for 8+ glasses daily
• Manage fever: Take paracetamol (acetaminophen) or ibuprofen as directed
• Soothe throat: Use throat lozenges, warm honey-lemon water, or salt water gargles
• Monitor symptoms: Check temperature and oxygen levels if available
• Isolate: Stay in a separate room from household members if possible
• Know warning signs: Seek care for difficulty breathing, chest pain, or confusion

Antiviral Medications

Several antiviral medications have been authorized for treating COVID-19 in high-risk individuals. These medications are most effective when started early and are typically prescribed for people at elevated risk of severe disease based on age, vaccination status, or underlying conditions.

Hospital Treatment for Severe Cases

Approximately 2-3% of COVID-19 cases require hospitalization, with rates higher among unvaccinated individuals and those with risk factors. Hospital treatment focuses on supporting organ function while the immune system clears the infection and inflammation subsides.

Supplemental oxygen is the cornerstone of treatment for COVID-19 pneumonia. For less severe cases, this may be delivered through nasal prongs or face masks. More severe cases may require high-flow oxygen, non-invasive ventilation, or mechanical ventilation in an intensive care unit. Prone positioning (lying face-down) has been shown to improve oxygenation in many patients.

Corticosteroids, particularly dexamethasone, have been proven to reduce mortality in hospitalized patients requiring oxygen. These medications work by dampening the excessive inflammatory response that contributes to lung damage. Other treatments may include anticoagulants to prevent blood clots, and in some cases, medications targeting specific inflammatory pathways.

What Is Long COVID?

Long COVID (post-COVID condition) refers to symptoms that persist or develop 4+ weeks after initial COVID-19 infection. Common symptoms include fatigue, brain fog, shortness of breath, heart palpitations, and joint pain. An estimated 10-30% of COVID-19 survivors experience some degree of long COVID, with symptoms lasting months to years in some cases.

Long COVID has emerged as a significant public health concern, affecting millions of people worldwide. Unlike the acute illness, which typically resolves within 1-2 weeks, long COVID can persist for months or even years, significantly impacting quality of life, ability to work, and daily functioning. The condition is recognized by the World Health Organization and has its own ICD-10 code (U09.9).

The exact mechanisms behind long COVID are still being studied, but several theories have been proposed. These include persistent viral reservoirs in certain tissues, autoimmune responses triggered by the initial infection, damage to blood vessels and organs during acute illness, and dysregulation of the immune system or nervous system. Multiple mechanisms may contribute in different individuals.

Importantly, vaccination appears to reduce the risk of long COVID by approximately 50% among those who experience breakthrough infections. Prior infection combined with vaccination ("hybrid immunity") seems to provide even greater protection. This is yet another reason why staying up-to-date on COVID-19 vaccination is recommended.

Common Long COVID Symptoms

• Fatigue: Overwhelming tiredness that doesn't improve with rest; often worsened by physical or mental exertion (post-exertional malaise)
• Brain fog: Difficulty concentrating, memory problems, confusion, slowed thinking
• Shortness of breath: Breathlessness with normal activities or at rest
• Heart palpitations: Racing heart, irregular heartbeat, chest discomfort
• Orthostatic intolerance: Dizziness, lightheadedness, or racing heart when standing (POTS-like symptoms)
• Sleep problems: Insomnia, unrefreshing sleep, altered sleep patterns
• Joint and muscle pain: Persistent aches and pains throughout the body
• Persistent loss of taste/smell: Continued changes to smell or taste perception
• Depression and anxiety: Mood changes, often related to dealing with chronic illness

Managing Long COVID

There is currently no specific cure for long COVID, and treatment focuses on managing individual symptoms and supporting gradual recovery. A multidisciplinary approach involving primary care providers, specialists, and rehabilitation professionals often works best. Pacing activities to avoid triggering post-exertional malaise is important for many patients.

If you're experiencing persistent symptoms after COVID-19, consult with your healthcare provider. They can rule out other conditions, address treatable symptoms, and connect you with appropriate specialists or rehabilitation programs. Many healthcare systems have established long COVID clinics to provide coordinated care for affected patients.

How Can You Prevent COVID-19?

Prevention strategies include staying up-to-date on COVID-19 vaccination, practicing good hand hygiene, improving indoor ventilation, wearing masks in high-risk settings, and staying home when sick. Vaccination remains the most effective way to prevent severe disease, hospitalization, and death from COVID-19.

While COVID-19 has become endemic and complete avoidance of the virus is unlikely, several measures can reduce your risk of infection and, importantly, reduce the severity of illness if you do become infected. The relative importance of different prevention strategies may vary based on current community transmission levels and individual risk factors.

Vaccination is the cornerstone of COVID-19 prevention. COVID-19 vaccines have proven remarkably effective at preventing severe illness, hospitalization, and death. While vaccine effectiveness against infection has declined with newer variants and time since vaccination, the protection against severe outcomes remains strong. Staying up-to-date with recommended booster doses helps maintain optimal protection.

Beyond vaccination, multiple layers of protection work together to reduce transmission risk. These measures are particularly important in high-risk settings like healthcare facilities, for individuals at elevated risk of severe disease, and during periods of high community transmission.

Key Prevention Strategies

• Get vaccinated: Complete your primary series and stay current on recommended boosters
• Practice hand hygiene: Wash hands frequently with soap for 20 seconds; use hand sanitizer when soap isn't available
• Improve ventilation: Open windows, use air filtration (HEPA filters), maximize outdoor air in HVAC systems
• Wear masks when appropriate: High-quality masks (N95, KN95, KF94) provide best protection in crowded or poorly ventilated indoor spaces
• Stay home when sick: If you have symptoms, test for COVID-19 and avoid contact with others until recovered
• Know your risk: Take extra precautions if you or close contacts are at high risk for severe disease
• Cover coughs and sneezes: Use a tissue or your elbow to prevent spreading respiratory droplets

COVID-19 Vaccination

COVID-19 vaccines have been one of the most impactful public health interventions in recent history. Available vaccines use different technologies—mRNA vaccines (Pfizer-BioNTech, Moderna), viral vector vaccines (Johnson & Johnson, AstraZeneca), and protein subunit vaccines (Novavax)—but all train the immune system to recognize and fight SARS-CoV-2.

Vaccine recommendations are updated periodically based on the latest evidence and circulating variants. In most countries, primary vaccination consists of 1-2 doses depending on the vaccine type, followed by booster doses at recommended intervals. Updated vaccines targeting recent variants are typically released annually, similar to seasonal flu vaccines. Check with your local health authority for current recommendations specific to your age and health status.

When Should You Seek Medical Care for COVID-19?

Seek medical care if you're at high risk and test positive (you may qualify for antiviral treatment), if symptoms worsen after initial improvement, or if you develop warning signs like difficulty breathing. Call emergency services immediately for severe breathing problems, chest pain, confusion, or bluish discoloration of lips or face.

Most people with COVID-19 can recover at home with supportive care. However, knowing when to seek medical attention is crucial for ensuring the best possible outcomes. Early medical consultation is particularly important for high-risk individuals who may benefit from antiviral treatment.

If you're in a high-risk category and develop COVID-19 symptoms, contact your healthcare provider promptly—ideally on the same day you test positive. Antiviral medications like Paxlovid work best when started within 5 days of symptom onset, so time is important. Many healthcare systems offer telehealth consultations for COVID-19, making it easier to access care without leaving home.

When to Contact Your Healthcare Provider

• You're high-risk and test positive: Discuss whether antiviral treatment is appropriate
• Symptoms worsen after improving: This could indicate a secondary infection or worsening inflammation
• Fever persists beyond 3-4 days: Prolonged fever may need medical evaluation
• You're unable to stay hydrated: Persistent vomiting or inability to drink fluids
• New symptoms develop: Especially breathing difficulties or chest discomfort
• You're concerned: Trust your instincts if something doesn't feel right