Symptomatic COVID patients are FOUR TIMES as likely to spread virus

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COVID-19 patients who develop symptoms are four times as likely to spread the virus as those who are asymptomatic, a new study finds. 

Researchers from the University of Georgia in Atlanta and the Zhejiang Provincial Center for Disease Control and Prevention in Hangzhou, China, looked into COVID-19 transmission data in the Zhejiang province in the south east part of the country.

They found the virus was most likely to transmit from one person to another in the window between two days before a person first experiences symptoms and three days after.

The findings helps provide scientists with a better look into which patients are the most likely to spread the virus and how quickly.

Researchers found that symptomatic COVID-19 patients are four times as likely to spread the virus as asymptomatic patients. Moderate COVID-19 patients are 4.3 times as likely to spread the virus

COVID-19 patients are most contagious during the window starting two days before first experiencing symptoms and three days after, with the risk increasing by 30% in this window

For the study, published in JAMA Internal Medicine, the team gathered data from 730 patients in the Zhejiang province from January 8 to July 30, 2020.

Researchers used existing contact tracing data to find 8,852 close contacts to those patients during the time they were contagious.

Close contacts who interacted with a COVID-19 patient between two days before, or three days after, the first appearance of their symptoms were more likely to catch the virus. 

The risk of transmission increased by around 30 percent, implying that patients are more contagious during that window of time.

'Our study suggests that transmission of COVID-19 is most likely if contacts are exposed shortly before and after symptom onset in the index patient,' the authors wrote.

Contracting COVID-19 from a symptomatic person makes a person more likely to have symptoms themselves. Those who are believed to have caught Covid from someone with symptoms were only 30% as likely to be asymptomatic

People who contracted the virus and did not show any symptoms were also less likely to spread it.

Researchers found that those with mild COVID-19 symptoms were four times as likely to spread the virus than someone who was asymptomatic. 

Patients with moderate symptoms were 4.3 times as likely to spread the virus when compared to asymptomatic people.

Those who contracted the virus from a symptomatic person were also around 30 percent as likely to have an asymptomatic case as those who contracted the virus from someone without symptoms.

'We found that contacts exposed to asymptomatic index patients were less likely to develop COVID-19, and, given infection, were more likely to be asymptomatic,' the  researchers wrote.

'This result suggests that there may be a dose-response association between severity of the index patient’s case of COVID-19 and clinical presentation among contacts. 

'If confirmed in other studies, this result may suggest additional secondary benefits associated with reducing case severity of individuals with COVID-19 through vaccination or prompt diagnosis and treatment.'

The research team believes these findings could be a key to understanding the virus, how it spreads, and how to perform contact tracing.

Reducing symptoms also seems to reduce spread, meaning that getting vaccinated could be even more important. 

'These results have important implications for understanding transmission dynamics of COVID-19 and are consistent with recent results suggesting that viral load may peak at two days before symptom onset and decline quickly after one week of symptoms,' they wrote.