| Setting | Proportion | Comment |
| Diamond Princess cruise ship, Yokohama, Japan (n=-634 tested positive). [1] | 18% (95% credible interval 16%-20%). | Most infections occurred before the quarantine start. |
| Vo’Euganeo, 50 km west of Venice, Italian village [2] | 50% to 75%—were asymptomatic | In an open letter to the authorities in the Tuscany region |
| MERS-CoV [3] | Increased from 0% to 29% over time | As the MERS-CoV progressed over time there was more identification of asymptomatic individuals due to increased surveillance and contacts testing. |
| 328 adults in Shanghai [4] | 13 (4%) patients were asymptomatic | |
| Japanese nationals evacuated from Wuhan (n=565) [5] | 31% (95% CI: 7.7% to 54%) | Based on temperature screening before disembarkation, interviews on symptoms including fever, cough, and non-specific symptoms |
| 23 Residents of a Long-Term Care Nursing Facility King County, Washington[6] | 10 (43%) had symptoms, and 13 (57%) were asymptomatic. Seven days after testing, 10 of 13 asymptomatics developed symptoms | Symptom-based screening could fail to identify approximately half of nursing home residents with COVID-19. |
| Airport screening of travellers [7] | 17% undetectable by typical screening procedures | Based on: A familial cluster of pneumonia associated with the 2019 novel coronavirus indicating person-to-person transmission: Lancet. 2020;0(0):S0140-6736(20)30154-9. |
| Hospitalised in Beijing, China (n=262)[8] | 13 (5.0%) asymptomatic cases | |
| 391 cases including 148 family index cases in Zhejiang Province [9] | 54 (14%) asymptomatic | higher family secondary attack rate, the secondary attack rate of spouses is higher than other family members. |
| Chinese perspective [10] | Over the past few days, asymptomatic patients were found in many Chinese cities. | Whether asymptomatic people can transmit SARS‐CoV‐2 to others is unclear. Another uncertainty is whether those who are asymptomatic can cause large‐scale infections. |
| 36 children, Zhejiang, China [11] | Asymptomatics, 10 (28%) | 7 had acute upper respiratory symptoms (19%) |
| Data-based analysis, modelling and forecasting of the COVID-19 outbreak [12] | | The number of asymptomatic and mild cases with subclinical manifestations that probably did not present to hospitals for treatment may be substantial; these cases, which possibly represent the bulk of the COVID-19 infections, remain unrecognized, |
| 166 new infections in China [13] | four-fifths of cases are asymptomatic, China figures indicate | Numbers quoted not verifiable |
| Nanjing, China (n=24) [14] | | 5 (21%) developed symptoms (fever, cough, fatigue and etc.) during hospitalization. |
| 450 case reports from 93 Chinese cities. [15] | | estimate that people who had not yet developed symptoms transmitted around 10% of the cases they studied. |
| People’s Hospital of Daofu county. Tibetan population (n=83) [16] | Asymptomatic carriers 22% | median age of asymptomatic carriers was 31 years and 1/3rd were students, aged <20 years. |
| WHO Q&A: Similarities and differences – COVID-19 and influenza [17] | suggest that 80% of infections are mild or asymptomatic, | |
| Iceland [18] | 50% of the people who tested positive had no symptoms.” | See also: First results of the voluntary screening in Iceland[19] |
| CDC [20] | A significant number of individuals that are infected actually remain asymptomatic. That may be as many as 25%. | |
| Interim Clinical Guidance for Management of Patients with Confirmed Coronavirus Disease [21] | Among children in China, illness severity was lower with 94% having asymptomatic, mild or moderate disease, | |
| Northern Italy, 60 volunteer blood donors [22] | 40 (67%) tested positive | |
