How many days after covid are you contagious
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Contagious Period After COVID-19 Infection
Incubation Period and Symptom Onset
The incubation period for COVID-19, the time between exposure to the virus and the onset of symptoms, is typically around 5.1 days, with 97.5% of individuals developing symptoms within 11.5 days of infection1. This period is crucial for understanding when an individual might start being contagious.
Duration of Infectiousness
Mild to Moderate Cases
For individuals with mild to moderate COVID-19, the period of infectiousness generally lasts up to 10 days from the onset of symptoms. Studies have shown that the virus is rarely isolated beyond this period in such cases2 7. This suggests that these patients are unlikely to be contagious after 10 days.
Severe or Critical Cases
In contrast, patients with severe or critical illness, or those who are immunocompromised, may remain infectious for a longer period. In some cases, the virus has been isolated up to 20 days after symptom onset, and in rare instances, up to 32 days2 7. This extended period of infectiousness necessitates longer isolation for these patients.
Asymptomatic and Presymptomatic Transmission
Asymptomatic individuals, who do not develop symptoms, can still be contagious. The median infectious period for asymptomatic cases is estimated to be between 6.5 to 9.5 days3. Additionally, presymptomatic transmission, where individuals spread the virus before showing symptoms, can occur within 1 to 4 days before symptom onset3.
Viral Shedding and RT-PCR Testing
RT-PCR tests, which detect viral RNA, have shown that viral shedding can continue for an average of 20 days from symptom onset, with some patients testing positive even after two consecutive negative tests4. However, the presence of viral RNA does not necessarily indicate that the virus is still infectious, as non-replicating viral particles can be detected long after the infectious period has ended7.
Conclusion
In summary, individuals with mild to moderate COVID-19 are generally not contagious beyond 10 days from symptom onset. Those with severe illness or compromised immune systems may remain infectious for up to 20 days or more. Asymptomatic individuals can also spread the virus, typically for about a week. Understanding these timelines is essential for effective isolation and public health measures to control the spread of COVID-19.
Sources and full results
Most relevant research papers on this topic
The Incubation Period of Coronavirus Disease 2019 (COVID-19) From Publicly Reported Confirmed Cases: Estimation and Application
The median incubation period for COVID-19 is 5.1 days, similar to SARS, supporting current quarantine or active monitoring recommendations for potential exposed individuals.
Meta-Analysis
Rigorous Journal
Highly CitedThe duration of infectiousness of individuals infected with SARS-CoV-2
COVID-19 patients with mild-to-moderate illness are highly unlikely to be infectious beyond 10 days of symptoms, but those with severe-to-critical illness or immunocompromised may shed infectious virus for longer.
Systematic ReviewHighly CitedInferred duration of infectious period of SARS-CoV-2: rapid scoping review and analysis of available evidence for asymptomatic and symptomatic COVID-19 cases
Inferring the infectious period of COVID-19 from repeated diagnosis, viral loads, and replication data alone has limitations and potential patient recall bias, but data provides a preliminary evidence base for models.
Systematic ReviewRigorous JournalHighly CitedDynamic profile of RT-PCR findings from 301 COVID-19 patients in Wuhan, China: A descriptive study
The average contagious period of COVID-19 patients is 20 days, with patients 65 years old needing longer observation and more than 2 series of negative viral tests.
Observational StudyHighly CitedThe First 75 Days of Novel Coronavirus (SARS-CoV-2) Outbreak: Recent Advances, Prevention, and Treatment
SARS-CoV-2 has been highly contagious and highly transmissible, with combined antiviral treatment showing the highest success rate in treating infected patients.
Literature ReviewRigorous JournalHighly CitedCOVID-19 and eye banking
COVID-19 is highly contagious and can be transmitted through respiratory droplets, contact with infected individuals, and ocular surface contact.
Duration of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) Infectivity: When Is It Safe to Discontinue Isolation?
SARS-CoV-2 infectivity rapidly decreases to near-zero after 10 days in mild-moderately ill patients and 15 days in severely-critically ill and immunocompromised patients, with the longest interval associated with replication-competent virus being 20 days from symptom onset.
Literature ReviewHighly CitedA Systematic Review of COVID-19 Epidemiology Based on Current Evidence
Current evidence suggests that COVID-19 epidemics take 3-7 days to double in size, with an incubation period of 4-6 days and a case fatality risk of 0.3% to 1.4% outside China.
Systematic ReviewRigorous JournalHighly CitedCOVID-19: clinical and laboratory manifestations in novel coronavirus infection
COVID-19 is a highly contagious disease caused by the coronavirus SARS-CoV-2, with high mortality in a small portion of infected individuals, and nonspecific laboratory biomarkers can predict complications and help identify asymptomatic carriers or mild symptoms.
Highly CitedSerial interval of novel coronavirus (COVID-19) infections
Abstract Objective To estimate the serial interval of novel coronavirus (COVID-19) from information on 28 infector-infectee pairs. Methods We collected dates of illness onset for primary cases (infectors) and secondary cases (infectees) from published research articles and case investigation reports. We subjectively ranked the credibility of the data and performed analyses on both the full dataset (n = 28) and a subset of pairs with highest certainty in reporting (n = 18). In addition, we adjust for right truncation of the data as the epidemic is still in its growth phase. Results Accounting for right truncation and analyzing all pairs, we estimated the median serial interval at 4.0 days (95% credible interval [CrI]: 3.1, 4.9). Limiting our data to only the most certain pairs, the median serial interval was estimated at 4.6 days (95% CrI: 3.5, 5.9). Conclusions The serial interval of COVID-19 is close to or shorter than its median incubation period. This suggests that a substantial proportion of secondary transmission may occur prior to illness onset. The COVID-19 serial interval is also shorter than the serial interval of severe acute respiratory syndrome (SARS), indicating that calculations made using the SARS serial interval may introduce bias.
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