Study: Incubation times of SARS-CoV-2 variants fell over time
As the dominant circulating strain of SARS-CoV-2 evolved from Alpha to Omicron, the incubation period from infection to symptoms or first positive COVID-19 test result gradually decreased, from 5 to 3.4 days, according to a systematic review and meta-analysis published today in JAMA Network Open.The incubation period is the time from exposure to a pathogen like a virus to the time of first symptoms of the disease that the pathogen causes.Peking University researchers led the analysis of 142 studies of 8,112 COVID-19 patients published from Dec 1, 2019, to Feb 10, 2022.
Of the studies, 45 were considered to present strong evidence, 82 were deemed moderate, and 15 were considered weak.Most studies (65.5%) were conducted from January to March 2020, and 76.1% were conducted in China.
The remaining studies came from multiple countries (1 study) or from South Korea (6), France (4), Japan (3), Singapore (2), India (2), Vietnam (2), and Australia (2).
A total of 83.8% of the studies included patients infected with the wild-type SARS-CoV-2 strain, while 3.5% included patients infected with multiple strains, and 7.7% involved unknown strains.Longer incubation at ends of age spectrumThe average pooled incubation of all variants was 6.57 days (range, 1.80 to 18.87).
United States
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Cases: 46 252 513
Deaths: 750 423
Recovered: 0
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India
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Cases: 34 321 025
Deaths: 459 652
Recovered: 0
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Brazil
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Cases: 21 835 785
Deaths: 608 235
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United Kingdom
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Cases: 9 215 683
Deaths: 141 607
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Russia
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Cases: 8 494 589
Deaths: 237 619
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