80% of patients have mild, self-resolving illness requiring no intervention.
A study compared ~46,000 patients hospitalized with influenza during the 2018–2019 flu season and 90,000 hospitalized with COVID-19 from March through April. The in-hospital mortality rate for COVID-19 was 3 times higher than influenza (17% vs. 6%). For adolescents, in-hospital mortality was 10 times higher with COVID-19 (1.1% vs. 0.1%). COVID-19 patients were more likely than flu patients to develop acute respiratory failure, pulmonary embolism, septic shock, or hemorrhagic stroke but were less likely to experience myocardial infarction or atrial fibrillation (90).
Observational data from Indiana found the infection fatality ratio of 0.26% of those not institutionalized aged 12 and older. Higher infection fatality ratios were seen in those aged 60 and older (1.71%) (this does not include those in nursing homes, rehabilitation centers, etc.) and among non-whites (0.59%). The infection fatality ratio of those aged 65 and older for the seasonal influenza is ~0.8% (91).
U.S. mortality compared to other western countries: mortality data through September 19, 2020 found the mortality rate in the U.S. was 60.3/100,000 compared to Australia (3.3 deaths per 100,000), Canada (24.6 per 100,000), Italy (59.1/100,000), and Belgium (86.8 per 100,000).
CDC data on prognosis in those under age 20 years found:
~70% of deaths occurred in those aged 10 through 20 years, 20% aged 1 through 9, and 10% under 1 year with Black and Latino youth accounting for ~75% of those who died.
Predisposing conditions of those who died include chronic lung disease (mostly asthma), obesity, neurologic/developmental conditions, and cardiovascular syndromes (92).
Duration of immunity from infection is unknown. While reinfection has occurred with other coronaviruses, they typically occur months to years after the initial infection (93).
Immunity persistence is unclear; from a study of 82 confirmed and 58 probably cases of COVID-19 from China, the median duration of IgM detection was 5 days (interquartile range, 3-6), while IgG was detected at a median of 14 days (interquartile 10-18) after symptom onset (94).
A small U.S. study followed antibody levels after mild COVID-19 in 34 patients with mild COVID-19 using serial anti-SARS-CoV-2 receptor binding domain IgG levels. The estimated mean IgG half-life was 36 days (95).
There remains conflicting data on persistence of antibody response in those already infected with the virus, with some showing loss of antibodies within a few weeks, while others show persistence up to 120 days after infection (96).
A recent report on 185 adults who recovered from COVID-19 (most with mild symptoms found levels of spike-specific memory B cells increased over the initial 4-6 months with SARS-CoV-2 spike IgG titers, showing only modest declines at 6-8 months (97).
U.S. cohort data tracked estimated excess deaths in the U.S. between March 1 and May 30, 2020, and compared it to data from January 5, 2015 through January 25, 2020. During these three months in 2020, there were 780,975 total deaths; 122,300 more deaths than expected from previous years, with COVID-19 accounting for 78% of these deaths, implying significant under-reporting (98).
Laboratory findings that correlate with an increased mortality include leukocytosis with lymphopenia, and highly-elevated LFTs, creatinine, lactate dehydrogenase, troponin, N-terminal-pro-brain natriuretic peptide, and d-dimer compared to those who recovered.
Morbidities that correlate with death include acute respiratory distress syndrome, sepsis, acute cardiac injury, heart failure, acute kidney injury, and encephalopathy (99).
UK cohort data of neurologic outcomes of COVID infection included cerebrovascular events and mental status changes (encephalopathy, encephalitis) (100).
Postinfection neuropsychiatric disorders were studied in a systematic review and meta-analysis of 65 studies and 7 preprints from multiple countries.
An Italian cohort study of 143 patients hospitalized for COVID-19 evaluated symptoms at a mean of 60 days after symptom onset and 36 days after hospital discharge. Mean age of 56.5 years, 37% were women, and the mean length of hospitalization was 13.5 days. During hospitalization, 73% had interstitial pneumonia, 15% required noninvasive ventilation, and 5% received mechanical ventilation. Participants were virus-free by PCR. Only 13% of participants reported being symptom-free but 55% had 3 or more symptoms. The most common persistent symptoms were fatigue 53%, dyspnea 43%, joint pain 27%, and chest pain 22%. Compared to pre-COVID-19 infection, 44% reported their quality of life was ≥10 points lower on a scale of 0 (worst health) to 100 (best health) (102).