COVID-19 signs, symptoms and severity of disease: A clinician guide

Last updated: June 1, 2022

The information below is based on currently available scientific evidence and informed by expert clinician opinion, and is subject to change as new information becomes available. This document is intended to provide clinicians with interim information on currently known clinical features of COVID-19, including signs and symptoms, incubation period, disease severity and risk factors for severe disease and SARS-CoV-2 variants of concern.

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Signs and symptoms

COVID-19 includes clinical features that present in varying ways with respect to frequency and severity and vary by age, vaccination status and variants of concern. Published reports often over-represent individuals who have more severe symptoms, and these may differ across care settings and between different age groups and vaccine statuses. Symptoms that are absent at the onset of illness may develop over time with disease progression. To date, there remains no comprehensive list of symptoms that has been validated to have high specificity or sensitivity for COVID-19. The ZOE COVID Study from the United Kingdom is a comprehensive system that tracks COVID-19 symptoms. This study found that symptom frequency and severity has varied by circulating variant and by vaccination status. During the Omicron wave that began in November 2021, those who have had at least 2 vaccinations reported milder symptoms; typical symptoms reported during the Omicron wave included runny nose, headache, sneezing, and sore throat. This response is different than the predominant symptoms earlier in the pandemic, which included fever, cough, chills and muscle pain. When fever occurred in Omicron cases, it was more frequently reported in unvaccinated than in vaccinated cases.

As new variants emerge and more of the population becomes vaccinated, there will be ongoing changes in the patterns of symptoms that individuals experience. With Omicron, clinical presumptive diagnosis should be considered with symptoms compatible with COVID-19 and a history of contact with known case(s). Testing may either not be available, or accurate, early in the course of illness. The patient however, should be advised to take a Point of Care antigen or NAAT test for SARS-CoV-2, when and where available, and follow local/regional public health authority recommendations for cases and contacts. Patients should always be encouraged to seek medical consultation if experiencing worsening symptoms of concern. Table 1 below outlines the common, less frequent, and rare symptoms reported by those with COVID-19 during the Omicron wave.

Table 1: Common, less frequent and rare symptoms for individuals with COVID-19 during the Omicron wave
Common symptoms
Less frequent symptoms
(≤ 50%)
Rare symptoms
  • Runny nose
  • Sneezing
  • Sore throat
  • Headache
  • Persistent cough
  • Joint pain
  • Chills
  • Fever
  • Dizziness
  • Muscle pain
  • Gastrointestinal symptoms (nausea, diarrhea, abdominal pain)
  • Hoarse voice
  • New loss of or altered sense of smell
  • Swollen glands
  • Chest pain
  • Irregular heartbeat
  • Shortness of breath
  • Skin changes
  • Delirium
  • Confusion/brain fog
Note: It is important to evaluate whether the patient's symptoms are new, worsening, or different from their baseline.

With the Omicron variant, loss or altered sense of smell is less prevalent than with the Delta variant, and sore throat and hoarse voice were significantly more prevalent. Those infected during the Omicron wave are less likely to experience at least one out of the three classic COVID-19 symptoms (fever, loss of smell, and persistent cough) compared with individuals infected during the Delta wave. Duration of acute symptoms for those with the Delta variant was longer than those with the Omicron variant (mean duration 9 days vs. 7 days). Regardless of the variant, the duration of symptoms is shorter for those who received three doses of vaccines (Delta mean duration 8 vs. Omicron duration 4 days). Some people can present symptoms for weeks of months after their initial recovery. See long COVID for details on symptoms, mental health, prevention, diagnosis and treatment.

Clinicians should remain aware of signs and symptoms that warrant more urgent or emergency medical attention. Patients with mild disease should be informed to seek medical attention should they experience any of the following:

Multisystem inflammatory syndrome – children (MIS-C)

In early 2020, MIS-C was newly confirmed to be associated with to SARS-CoV-2 infection. It is characterized by hyperinflammation and multi-organ involvement, and presents with clinical features similar to Kawasaki disease and toxic shock syndrome. Symptoms typically occur around 2-6 weeks after the initial infection. In Canada, MIS-C is rare, with 269 cases reported to the Public Health Agency of Canada between March 11, 2020 and October 2, 2021. Cases have been reported in infants as young as one week to youth as old as 18 years, with a median age of six years. Cases were more likely to occur in males than females (58% vs 42%). Almost all MIS-C cases (99%) required hospitalization and 36% required intensive care unit admission. No deaths from MIS-C have been reported in Canada as of May 31, 2022.

Multisystem inflammatory syndrome – adults (MIS-A)

Multisystem inflammatory syndrome is a rare but severe complication of SARS-CoV-2 that may also occur in adults. Symptoms typically occur around 2-12 weeks after the initial infection. CDC has developed a working case definition for MIS-A.

In September 2021, a systematic review of all MIS-A publications reported a total of 221 cases, with a median age of 21 years and 70% of the cases being male. Most patients with MIS-A presented with fever (96%), hypotension (60%), cardiac dysfunction (54%), shortness of breath (52%), and/or diarrhea (52%). The median number of organ systems involved was 5. The median hospital stay was 8 days; and of those hospitalized, 57% were admitted to the intensive care unit (ICU). Of those admitted to the ICU, 47% required respiratory support and 7% died. Most patients had elevated markers of coagulopathy and/or inflammation (90%) and a positive SARS-CoV-2 serologic finding (72%).

Although rare, it is important to recognize the symptoms of MIS-A, as it is a serious hyperinflammatory condition associated with COVID-19 and can lead to multiorgan failure.

COVID-19 symptoms in children

In earlier waves of the pandemic, typical symptoms of COVID-19 in children were fever (46-64%) and cough (32-56%). However, many children were asymptomatic or only had a few symptoms. More recently, with the Omicron variant, symptoms have been shown to more likely be upper respiratory, as noted in Table 1 above. Young children are especially vulnerable to upper respiratory acute infection due to their small and relatively collapsible airways. This has resulted in some children experiencing laryngotracheobronchitis, or croup. Croup is classically characterized by a sudden onset "barking cough," inspiratory stridor, and respiratory distress. Some small case series of croup have been reported during the Omicron wave and have been associated with SARS-CoV-2 infection. It is still unknown if cases of croup are due to SARS-CoV-2 or a co-infection with another virus. Other than croup, children's symptoms mimic those of adults for Omicron, which are predominantly upper respiratory symptoms, including runny nose, sneezing and sore throat. Hospitalized children are more likely to have fever, abdominal symptoms like vomiting, and shortness of breath, along with cough and the other upper respiratory symptoms. Symptoms of COVID-19 may overlap with that of other viral infections, including influenza and other respiratory and enteric viral infections. The true incidence of asymptomatic COVID-19 infection is unknown. However, asymptomatic COVID-19 infection has been reported in up to 45% of children who had surveillance testing done at the time of hospitalization for a non-COVID indication.

A MMWR report on hospitalized children aged 5-11 years with SARS-CoV-2 infections in 14 U.S. states found that during the Omicron wave, unvaccinated children had double the rate of hospitalization compared to vaccinated children. Thirty percent (30%) of hospitalized children had no underlying medical conditions, and children with diabetes and obesity were more likely to develop severe COVID-19. Intensive care unit admission occurred in 19% of hospitalized cases. Increasing COVID-19 vaccination coverage among children aged 5–11 years, especially those at higher risk of severe disease, may help prevent hospitalizations and severe outcomes associated with COVID-19.

When assessing children, it is important to consider that the signs and symptoms of COVID-19 are similar to those of other infectious and non-infectious conditions, including influenza, other viral upper respiratory infections, streptococcal pharyngitis, asthma and allergies. The lack of specificity of signs or symptoms and the significant proportion of asymptomatic infections makes symptom-based screening for identification of SARS-CoV-2 in children difficult.

COVID-19 symptoms in older adults

Older adults may present with atypical symptoms due to age-related weakening of the immune system. Weakened immunity can also lead to increased risk of infection. Clinical presentation may differ in older adults, and COVID-19 symptoms may need to be evaluated using a slightly different approach in this patient population.

Symptoms that may present differently in older individuals include: fever (may present with lower temperatures), cough and shortness of breath (differentiate from chronic lung conditions), loss of taste or smell (differentiate if due to medications or neurodegenerative processes causing sensory impairment), and fatigue and body ache (common in older individuals). Sore throat, new-onset congestion, nausea, vomiting, or diarrhea may be more valuable as diagnostic criteria for SARS-CoV-2 infection in older individuals.

In a multicenter study of seven emergency departments in the US, delirium was one of the presenting symptoms in 226 (28%) of 817 patients with COVID-19 and exclusively the primary presenting complaint in 16% of patients with a mean age of 78 years. Estimates of falls and frailty, as a presenting symptom of COVID-19, ranged between 23.5% and 32%. In addition, dehydration in older adults should be considered as an important presentation of COVID-19. Therefore, it is important to ensure older adults receive their recommended vaccination series and boosters as they become available via regional/provincial/territorial public health authorities.

To review the most up-to-date information on Age groups by hospitalizations, ICU admissions and deaths see COVID-19 epidemiological summary.

Asymptomatic infection

A person who is asymptomatic is someone who has tested positive for SARS-CoV-2 test and has never developed any symptoms. During the Omicron wave, a large study in South Africa estimated that 31% of cases were asymptomatic (approximately 1 in 3 cases). This study also reported high viral loads in asymptomatic cases. The asymptomatic carriage rate was similar in SARS-CoV-2 seropositive and seronegative cases.

Incubation period

The pre-Omicron incubation period for COVID-19 had been estimated to range from 2 to 14 days, with a median of 4-7 days from exposure to symptom onset. Omicron has been found to have an incubation period of a median of 2-4 days, and its associated viral loads have been reported to peak in saliva 1-2 days before positive results can be seen in PCR or rapid antigen tests. Omicron has also been found to be more transmissible, have a higher attack rate and a higher basic reproduction number (R0) than other variants.

The world's first "human challenge" trial where volunteers were intentionally exposed to a challenge virus from the B1-lineage of SARS-CoV-2, which included the Alpha, Beta and Delta variants, found that the presence of symptoms did not change with viral load. The viral load in the airways in these infected patients was not related to whether the individual developed symptoms or the severity of illness. In infected individuals, the peak viral load occurred on day 5, with the virus first detected in the throat and then rising to significantly higher levels in the nose. The challenge study found that viral loads were detectable in the nose and throat within 24 hours of inoculation, although symptoms became apparent a little later, i.e., within 2-4 days.

It is now known that SARS-CoV-2 RNA can be detected in the upper or lower respiratory tract for weeks after illness onset. However, detection of viral RNA does not necessarily mean that a patient can transmit the virus. Evidence has shown that an individual may be infectious for up to 3 days prior to any presentation of symptoms. The levels of viral RNA from saliva, sputum, nasopharyngeal or other upper respiratory specimens, and stool samples appear to be highest soon after symptom onset.

Disease severity and risk factors for severe disease

There is a spectrum of COVID-19 disease severity, ranging from asymptomatic, mild, moderate, to severe and critical disease. Severe disease occurs more often in older age and in those with underlying medical conditions, and the risk increases with the number of underlying medical conditions.

The conditions identified below are those for which conclusive evidence is available.

Underlying medical conditions associated with more severe COVID-19 disease

Certain medical and/or social vulnerabilities, may make it more difficult for patients to recognize, clearly communicate, or act on symptoms' progression. Affected individuals may include: people experiencing intellectual, developmental, or cognitive disabilities; people who use substances regularly; people who live with mental health conditions; and persons experiencing homelessness or who are unhoused. These patients need closer attention and monitoring.

SARS-CoV-2 variants of concern (VOC)

The SARS-CoV-2 virus has naturally mutated or changed over time. Mutations may increase or decrease transmissibility or virulence, or lead to immune escape or reduced responses to therapeutics compared to non-variant viruses. Compared to the original strain of SARS-CoV-2, we have seen an increased transmissibility with Omicron. Over time, new variants will emerge, and the transmissibility and virulence will be expected to change.


Dr. Marianna Ofner, Dr. Marina Salvadori, Yung-En Chung, Dr. Michael Green, Aidan Pucchio, Denise Gravel-Tropper, Dr. Mireille Plamondon and Dr. Ewa Rajda.


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