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COVID-19 Most Transmissible 2 Days Before, 3 Days After Symptoms Appear: Study

COVID-19 Study: The researchers conducted contact tracing and studied COVID-19 transmission among approximately 9,000 close contacts of primary cases in the Zhejiang province of China from January 2020 to August 2020

COVID-19 Most Transmissible 2 Days Before, 3 Days After Symptoms Appear: Study
Highlights
  • Viral load has been used as an indirect measure of transmission: Expert
  • Experts conducted contact tracing, studied in 9.000 contacts of Covid cases
  • This study further emphasises the need for vaccination

Beijing: People infected with the SARS-CoV-2 virus, which causes COVID-19, are most contagious two days before, and three days after they develop symptoms, according to a study conducted in China. The research, published in the journal JAMA Internal Medicine, also found that infected individuals were more likely to be asymptomatic if they contracted the virus from a primary case — the first infected person in an outbreak — who was also asymptomatic.

Also Read: COVID-19 Bigger Blood Clot Threat Than Vaccines, UK Study Finds

“In previous studies, viral load has been used as an indirect measure of transmission,” said Leonardo Martinez, an assistant professor at Boston University School of Public Health (BUSPH) in the US.

We wanted to see if results from these past studies, which show that COVID cases are most transmissible a few days before and after symptom onset, could be confirmed by looking at secondary cases among close contacts, Mr Martinez said.

The researchers conducted contact tracing and studied COVID-19 transmission among approximately 9,000 close contacts of primary cases in the Zhejiang province of China from January 2020 to August 2020. “Close” contacts included household contacts — defined as individuals who lived in the same household or who dined together — co-workers, people in hospital settings, and riders in shared vehicles.

The researchers, including study co-lead Yang Ge from the University of Georgia College of Public Health, US, monitored infected individuals for at least 90 days after their initial positive COVID test results to distinguish between asymptomatic and pre-symptomatic cases. Of the individuals identified as primary cases, 89 per cent developed mild or moderate symptoms, and only 11 per cent were asymptomatic — and no one developed severe symptoms.

Also Read: Half Of Hospitalised Covid Patients Have Persisting Symptoms After A Year: Lancet Study

Household members of primary cases, as well as people who were exposed to primary cases multiple times or for longer durations of time, had higher infection rates than other close contacts.

However, regardless of these risk factors, close contacts were more likely to contract COVID-19 from the primary infected individual if they were exposed shortly before or after the individual developed noticeable symptoms.

Our results suggest that the timing of exposure relative to primary-case symptoms is important for transmission, and this understanding provides further evidence that rapid testing and quarantine after someone is feeling sick is a critical step to control the epidemic, Mr Martinez said.

In comparison to mild and moderate symptomatic individuals, asymptomatic primary individuals were much less likely to transmit COVID to close contacts — but if they did, the contacts were also less likely to experience noticeable symptoms, the researchers said.

This study further emphasises the need for vaccination, which reduces clinical severity among people that develop COVID, Mr Martinez added.

Also Read: What Are COVID-19 Breakthrough Infections? How Long Does Immunity Last After COVID-19 Vaccination? An Expert Explains

(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)

NDTV – Dettol Banega Swasth India campaign is an extension of the five-year-old Banega Swachh India initiative helmed by Campaign Ambassador Amitabh Bachchan. It aims to spread awareness about critical health issues facing the country. In wake of the current COVID-19 pandemic, the need for WASH (WaterSanitation and Hygiene) is reaffirmed as handwashing is one of the ways to prevent Coronavirus infection and other diseases. The campaign highlights the importance of nutrition and healthcare for women and children to prevent maternal and child mortality, fight malnutrition, stunting, wasting, anaemia and disease prevention through vaccines. Importance of programmes like Public Distribution System (PDS), Mid-day Meal Scheme, POSHAN Abhiyan and the role of Aganwadis and ASHA workers are also covered. Only a Swachh or clean India where toilets are used and open defecation free (ODF) status achieved as part of the Swachh Bharat Abhiyan launched by Prime Minister Narendra Modi in 2014, can eradicate diseases like diahorrea and become a Swasth or healthy India. The campaign will continue to cover issues like air pollutionwaste managementplastic banmanual scavenging and sanitation workers and menstrual hygiene

World

24,00,62,413Cases
20,17,73,183Active
3,33,99,961Recovered
48,89,269Deaths
Coronavirus has spread to 195 countries. The total confirmed cases worldwide are 24,00,62,413 and 48,89,269 have died; 20,17,73,183 are active cases and 3,33,99,961 have recovered as on October 16, 2021 at 4:08 am.

India

3,40,53,573 15,981Cases
2,01,6322,046Active
3,33,99,961 17,861Recovered
4,51,980 166Deaths
In India, there are 3,40,53,573 confirmed cases including 4,51,980 deaths. The number of active cases is 2,01,632 and 3,33,99,961 have recovered as on October 16, 2021 at 2:30 am.

State Details

State Cases Active Recovered Deaths
Maharashtra

65,88,429 2,149

33,379 222

64,15,316 1,898

1,39,734 29

Kerala

48,38,811 8,867

95,349 1,072

47,16,728 9,872

26,734 67

Karnataka

29,82,869 470

9,700 93

29,35,238 368

37,931 9

Tamil Nadu

26,84,641 1,245

15,238 213

26,33,534 1,442

35,869 16

Andhra Pradesh

20,59,708 586

6,453 135

20,38,960 712

14,295 9

Uttar Pradesh

17,10,014 6

133 2

16,86,984 8

22,897

West Bengal

15,79,463 451

7,513 63

15,52,997 506

18,953 8

Delhi

14,39,337 26

327 10

14,13,921 36

25,089

Odisha

10,34,276 467

4,817 73

10,21,180 535

8,279 5

Chhattisgarh

10,05,624 10

197 6

9,91,857 16

13,570

Rajasthan

9,54,383 1

40 2

9,45,389 3

8,954

Gujarat

8,26,258 14

212 3

8,15,960 17

10,086

Madhya Pradesh

7,92,675 6

106 5

7,82,046 11

10,523

Haryana

7,71,049 14

116 11

7,60,884 3

10,049

Bihar

7,26,021 5

46 4

7,16,314 1

9,661

Telangana

6,68,722 104

4,056 115

6,60,730 218

3,936 1

Assam

6,05,944 97

3,458 188

5,96,547 284

5,939 1

Punjab

6,01,992 21

228 6

5,85,224 25

16,540 2

Jharkhand

3,48,415 9

130 0

3,43,150 9

5,135

Uttarakhand

3,43,739 10

179 4

3,36,163 6

7,397

Jammu And Kashmir

3,30,885 51

895 40

3,25,564 91

4,426

Himachal Pradesh

2,21,203 90

1,361 26

2,16,125 114

3,717 2

Goa

1,77,410 54

648 31

1,73,423 81

3,339 4

Puducherry

1,27,296 37

611 36

1,24,836 73

1,849

Manipur

1,22,545 113

1,444 0

1,19,208 109

1,893 4

Mizoram

1,11,651 932

13,316 285

97,955 1,211

380 6

Tripura

84,299 4

102 8

83,381 12

816

Meghalaya

82,815 81

893 1

80,490 79

1,432 1

Chandigarh

65,297 2

30 2

64,447 4

820

Arunachal Pradesh

54,964 6

183 19

54,501 25

280

Sikkim

31,739 17

189 35

31,159 51

391 1

Nagaland

31,547 31

228 2

30,645 32

674 1

Ladakh

20,871 4

42 2

20,621 6

208

Dadra And Nagar Haveli

10,675

3 0

10,668

4

Lakshadweep

10,365

1 1

10,313 1

51

Andaman And Nicobar Islands

7,641 1

9 1

7,503 2

129

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