Important update: Healthcare facilities
CDC has updated select ways to operate healthcare systems effectively in response to COVID-19 vaccination. Learn more
Given new evidence on the B.1.617.2 (Delta) variant, CDC has updated the guidance for fully vaccinated people. CDC recommends universal indoor masking for all teachers, staff, students, and visitors to K-12 schools, regardless of vaccination status. Children should return to full-time in-person learning in the fall with layered prevention strategies in place.
The White House announced that vaccines will be required for international travelers coming into the United States, with an effective date of November 8, 2021. For purposes of entry into the United States, vaccines accepted will include FDA approved or authorized and WHO Emergency Use Listing vaccines. More information is available here.
Travel requirements to enter the United States are changing, starting November 8, 2021. More information is available here.

Clinical Presentation

Clinical Presentation

Clinical considerations for care of children and adults with confirmed COVID-19

Updated Oct. 19, 2022
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What You Need to Know
  • The clinical presentation of COVID-19 ranges from asymptomatic to critical illness. An infected person can transmit of SARS-CoV-2 before the onset of symptoms. Symptoms can change over the course of illness and can progress in severity.
  • Uncommon presentations of COVID-19 can occur, might vary by the age of the patient, and are a challenge to recognize.
  • In adults, age is the strongest risk factor for severe COVID-19. The risk of severe COVID-19 increases with increasing age over 40 years and with increasing number of certain underlying medical conditions.

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)


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

The NIH COVID-19 Treatment Guidelines group SARS-CoV-2 infection into five categories based on severity of illness:

  • Asymptomatic or pre-symptomatic infection: people who test positive for SARS-CoV-2 using a virologic test (i.e., a nucleic acid amplification test [NAAT] or an antigen test) but who have no symptoms that are consistent with COVID-19.
  • Mild illness: people who may have any of the various signs and symptoms of COVID-19 (e.g., fever, cough, sore throat, malaise, headache, muscle pain, nausea, vomiting, diarrhea, loss of taste and smell) but who do not have shortness of breath, dyspnea, or abnormal chest imaging.
  • Moderate illness: people who have evidence of lower respiratory disease during clinical assessment or imaging and who have an oxygen saturation (SpO2) ≥94% on room air at sea level.
  • Severe illness: people who have oxygen saturation <94% on room air at sea level, a ratio of arterial partial pressure of oxygen to fraction of inspired oxygen (PaO2/FiO2) <300 mm Hg, a respiratory rate >30 breaths/min, or lung infiltrates >50%
  • Critical illness: people who have respiratory failure, septic shock, and/or multiple organ dysfunction

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.


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.

Science Brief: SARS-CoV-2 Transmission

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