The current study summarized available retrospective studies, case reports from family-cluster, adults, children, health care workers, and travelers. Person to person asymptomatic transmission was observed among familial-cluster in an asymptomatic COVID-19 child aged ten years showed abnormal chest CT and another child with mild chest CT manifestation when his family members were diagnosed COVID-19 positive showing sign of fever and respiratory issues ^8,9. The study suggests that thorough epidemiological investigations in combination with multiple detection methods (e.g., RT-PCR, chest CT, Rapid IgM-IgG, and serum CRP level) can identify the asymptomatic carriers ^10,11 in the community among varying clinical manifestations between individuals. Another study supports the possibility of asymptomatic transmission among familial-cluster during the incubation period ¹². In a familial-cluster of 5 positive COVID-19 patients had contact with other asymptomatic family members who returned from the Wuhan, suggestive of asymptomatic transmission ⁷.

Studies included in the current meta-analysis were checked for the likelihood ratio (LR) between random effect and fixed-effect models for the distribution of asymptomatic COVID-19 transmission among the community.

Among pregnant woman’s fetuses are at high-risk during any disease outbreak, in pregnant woman with asymptomatic COVID-19 viral infection delivered a baby negative for the COVID-19 nucleic acid test Suggestive of no vertical transmission among neonates born to COVID-19 infected mothers ^14,42–49. In Wuhan, a lower fatality rate and higher discharge rate were observed than in Beijing. It is crucial to identify and take necessary control measures among adults of asymptomatic cases to prevent transmission ²¹. In South Korea, 41 asymptomatic adults were identified and were confirmed by RT-PCR out of 213 cases ¹⁷. Among 100 asymptomatic cases, 60% developed delayed symptoms, and none of the asymptomatic cases died, suggesting asymptomatic transmission during the incubation period ¹⁸. Another study did not observe any difference in the symptomatic and asymptomatic COVID-19 transmission rates among patients²². In adults, CT imaging of asymptomatic COVID-19 individuals has advantages in highly suspicious cases with negative nucleic acid testing ¹⁷. In adults, a serological investigation among 31 out of 34 cases with asymptomatic infection did not require oxygen support during hospitalization ¹⁵. Theoretically, the quantified infection transmission rate shows the estimated risk ratio (RR) of infectivity [3.9%, (95%CI: 1.5 – 11.8)] of symptomatic against asymptomatic.

In asymptomatic adults, the transmission was significantly smaller than that of the symptomatic cases ¹⁶. No gender difference among males and females was observed for asymptomatic transmission ²⁰.

Further longitudinal surveillance via virus nucleic acid testing is warranted to identify and control the viral load among asymptomatic CVOID-19 cases ²⁴ in adults. In a study, 4 asymptomatic cases were quarantined for 14 days, and none was able to transmit the infections due to managing proper isolation and quarantine of the cases ¹⁹.

Asymptomatic COVID-19 transmission was seen in children ²⁶. In a study, 24 asymptomatic cases were screened from close contacts of asymptomatic COIVD-19 ²⁵. Another study supports the multiple site sampling of close contacts should be performed ¹ among children. In a review, it was observed that the adults as compared to children with COVID-19 infection show mild clinical symptoms and radiological manifestations as previously reported for SARS- and the Middle East respiratory syndrome (MERS)-CoV ⁵⁰.

Health care workers in a nursing facility: Rapid transmission of COVID-19 had been reported in 76 residents cases. and 23 (30.3%) had positive test results, and approximately 13 were asymptomatic on the day of testing, suggesting the possibility of asymptomatic transmission of COVID-19 ²⁷. Establishing effective infection control strategies to prevent the transmission among frontline health care workers and patients from COVID-19 infections should be managed urgently and on priority. In another study, out of 48 participants observed, two asymptomatic cases become positive, suggesting appropriate symptom-based testing strategies are essential to prevent outbreaks of COVID-19 within hospital settings ²⁹. In the USA, health care workers not wearing respirators were exposed to an asymptomatic CVOID-19 patient without developing clinical illness ²⁸.

Traveler: In Korea, COVID-19 was transmitted by 16 infected travelers from other countries. The disease was infectious at this stage, which resulted from close contacts of asymptomatic carriers ³⁰. Most of the infections on board the Diamond Princess Cruise ship highlight the asymptomatic transmission of COVID-19 in confined settings. To further mitigate the transmissibility of COVID-19, it may be advised to minimize the number of gathering in confined settings ³². A 36-year-old traveler returned from Wuhan was found COVID-19 positive, and other health workers who were in close contact with the patients were also tested RT-PCR positive. However, the patient initially had no symptoms ³³. A higher proportion of asymptomatic (12%) was reported among travelers returning to Brunei. In another study, it was suggested to increase the testing facility for asymptomatic COVID-19 cases ³⁴. Similarly, an asymptomatic COVID-19 patient showed viral transmissibility without showing any signs and symptoms in travelers from China ³¹. Although, we recommend early isolation for and social distancing for asymptomatic COVID-19 cases, which may led to psychological and emotional loss as reported in qualitative study from UK⁵¹.