Incubation Period of COVID-19
The incubation period for COVID-19 is generally 5.2 days (range 1-14 days), with 97.5% of infected individuals developing symptoms within 11.5 days of exposure. 1, 2
Understanding the Incubation Period
The incubation period refers to the time from infection to the onset of symptoms. Based on the most recent and highest quality evidence, the incubation period of COVID-19 has the following characteristics:
- Median incubation period: 5.1-5.2 days 1, 2
- Mean incubation period: 5.84 days (95% CI, 5.42-6.25 days) 3
- Range: 1-14 days 1
- 97.5% of cases develop symptoms by: 11.5 days (95% CI, 8.2-15.6 days) 2
Variant-Specific Incubation Periods
More recent research has shown that the incubation period varies by SARS-CoV-2 variant 4:
- Alpha variant: 5.00 days (95% CI, 4.94-5.06 days)
- Beta variant: 4.50 days (95% CI, 1.83-7.17 days)
- Delta variant: 4.41 days (95% CI, 3.76-5.05 days)
- Omicron variant: 3.42 days (95% CI, 2.88-3.96 days)
This demonstrates a trend of decreasing incubation periods with newer variants, with Omicron having the shortest incubation period.
Age-Related Differences
The incubation period may vary by age 4:
- Older patients (>60 years): 7.43 days (95% CI, 5.75-9.11 days)
- Children (≤18 years): 8.82 days (95% CI, 8.19-9.45 days)
- Adults with non-severe illness: 6.99 days (95% CI, 6.07-7.92 days)
- Adults with severe illness: 6.69 days (95% CI, 4.53-8.85 days)
Clinical and Public Health Implications
Quarantine Duration: The 14-day quarantine period recommended by many health authorities is appropriate as it covers the incubation period for 97.5% of cases 2, 5.
Contagious Period: Unlike SARS-CoV, COVID-19 can be contagious during the incubation period, even before symptoms appear 1. This characteristic makes containment more challenging.
Viral Shedding: Viral shedding may begin 1-2 days before symptom onset and typically continues for 1-2 weeks in mild-moderate cases, but can extend beyond 2 weeks in severe cases 1.
Asymptomatic Transmission: Approximately 30-60% of individuals shedding the virus may be asymptomatic 1, highlighting the importance of preventive measures regardless of symptom status.
Monitoring and Isolation Recommendations
- Active monitoring or quarantine: 14 days is appropriate for potentially exposed individuals 2, 5
- Testing strategy: Testing should be considered even for asymptomatic individuals with known exposure
- Contact tracing: Should begin as soon as possible after a confirmed case is identified, considering the relatively short incubation period
Understanding the incubation period is crucial for effective disease control measures, including isolation protocols, contact tracing efforts, and quarantine duration recommendations.