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What percentage of people remain positive after a diagnosis of Covid-19?

The recent change in isolation policy for people in England was based on a modelling study by Bays et al which showed that “after the 5th day after a positive test, an estimated 31% of persons remain infectious”.

Reference:  Bays D, Whiteley T, Pindar M, et al. Mitigating isolation: The use of rapid antigen testing to reduce the impact of self-isolation periods. medRxiv 2021:2021.12.23.21268326. doi: 10.1101/2021.12.23.21268326 

Bays et al Table 3: Percentages (rounded to integer) of people who are still infectious after each day according to their disease profile

 

Day

 

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

Still infectious (%)

100

92

75

58

43

31

22

16

11

7

5

3

2

2

1

No-longer infectious (%)

0.0

8

25

42

57

69

78

84

89

93

95

97

98

98

99

 

Bays et al Table 4: Output from the model of the effect of the considered scenarios on disease release into the community (measured in three different ways) and the self-isolation in addition to that which is necessary to contain disease spread. Intervals are the 2.5 and 97.5 quantiles from the simulations.2

 

Policy

Released infectious (%)

Mean time a released person is infectious for (hours)

Mean excess isolation per person (hours)

7-day isolation

15.8% [11.9 - 21.0]

62.3 [56.5 - 69.2]

76.8 [67.2 - 84.0]

10-day isolation

5.1% [3.4 - 7.6]

59.3 [53.5 - 65.6]

141.6 [129.6 - 151.2]

14-day isolation

1.0% [0.6 - 1.8]

57.1 [51.4 - 63.1]

235.2 [220.8 - 247.2]

10-day isolation, or 1 negative tests from day 7

9.2% [6.5 - 12.8]

61.1 [55.3 - 67.5]

79.2 [69.6 - 86.4]

10-day isolation, or 2 negative tests from day 6

6.2% [4.2 - 9.0]

60.0 [53.9 - 66.3]

81.6 [72.0 - 88.8]

14-day isolation, or 2 negative tests from day 6

4.1% [2.6 - 6.0]

61.3 [55.8 - 67.7]

69.6 [64.8 - 74.4]

 

 

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