Clinical Presentation

Incubation Period

Data suggest that incubation periods may differ by variant of the virus. Meta-analyses of studies published in 2020 identified a pooled mean incubation period of 6.5 days from exposure to symptom onset.⁽¹⁾ A study conducted during high levels of Delta variant transmission reported an incubation period of 4.3 days,⁽²⁾ and studies performed during high levels of Omicron variant transmission reported a median incubation period of 3–4 days.^(3,4)

Presentation

The clinical presentation of COVID-19 ranges from asymptomatic to severe illness, and COVID-19 symptoms may change over the course of illness. Symptoms can overlap with those of other viral respiratory illnesses. Because symptoms may progress quickly, close follow-up is needed, especially for older adults, people with disabilities, people with immunocompromising conditions, and people with medical conditions that place them at greater risk for severe illness or death. People with COVID-19 may be asymptomatic or experience one or more of the following symptoms⁽⁵⁾:

• Fever or chills
• Cough
• Shortness of breath or difficulty breathing
• Fatigue
• Myalgia (Muscle or body aches)
• Headache
• New loss of taste or smell
• Sore throat
• Congestion or runny nose
• Nausea or vomiting
• Diarrhea

Asymptomatic and presymptomatic presentation

Studies have documented infection with SARS-CoV-2 in people who never develop symptoms (asymptomatic presentation) and in people who are asymptomatic when tested but then develop symptoms later (presymptomatic presentation).^(6,7) However, it is unclear what percentage of people who have asymptomatic infection progress to clinical disease (presymptomatic presentation). People can experience asymptomatic SARS-CoV-2 infection, including people who are up to date with their vaccines and people who were previously infected.⁽⁸⁾ Multiple publications have reported cases of people with abnormalities on chest imaging that are consistent with COVID-19 very early in the course of illness, even before the onset of symptoms or a positive COVID-19 test.⁽⁹⁾

Common COVID-19 symptoms

Fever, cough, shortness of breath, fatigue, headache, and myalgia are among the most commonly reported symptoms in people with COVID-19.⁽⁵⁾ Some people with COVID-19 have gastrointestinal symptoms such as nausea, vomiting, or diarrhea, sometimes prior to having fever or lower respiratory tract signs and symptoms.⁽¹⁰⁾ Loss of smell and taste may be reported initial symptoms of COVID-19.⁽¹¹⁾

Uncommon COVID-19 symptoms

Less common presentations of COVID-19 can occur. Older adults may present with different symptoms than children and younger adults. Some older adults can experience COVID-19 infection accompanied by delirium, falls, reduced mobility or generalized weakness, and glycemic changes.⁽¹²⁾

Several studies have reported ocular symptoms associated with COVID-19 infection, including redness, tearing, dry eye or foreign body sensation, discharge or increased secretions, and eye itching or pain.⁽¹³⁾

A wide range of dermatologic manifestations have been associated with COVID-19; timing of skin manifestations in relation to other COVID-19 symptoms and signs is variable.⁽¹⁴⁾ Some skin manifestations may be associated with increased disease severity.⁽¹⁵⁾ Images of cutaneous findings in COVID-19 are available from the American Academy of Dermatology.

Transmission

People who have asymptomatic or symptomatic infections can transmit SARS-CoV-2, with varying rates and timelines for transmission.⁽¹⁶⁾ Both people who have been vaccinated and those who have not been vaccinated can transmit virus.^(17,18) Clinicians should consider encouraging all people to test for COVID-19 as recommended by CDC, protect themselves and others from infection by getting vaccinated, wear a high-quality mask when recommended, and follow guidance based on community risk. Clinicians should also consider advising people who are infected with COVID-19 to follow CDC guidelines for isolation.

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