As we all know, the COVID-19 virus is highly contagious, but it has not been known when its transmission capacity will be strongest. Now, scientists may have revealed the answer. American scientists wrote in the latest issue of the Journal of the American Medical Association that their new research found that people infected with the COVID-19 virus are the most infectious two days before and three days after the onset, and asymptomatic infections occur. If it spreads, contacts are more likely to become asymptomatic infections.
Leonardo Martinez, an assistant professor of epidemiology at the Boston University School of Public Health, one of the research leaders, said: “Previously, scientists used viral load to indirectly measure infectious capacity, but we hope to observe the Following the case, to confirm whether the results of these past studies can be confirmed. These studies show that the COVID-19 virus is most likely to spread in the days before and after the symptoms appear."
From January 2020 to August 2020, Martinez and others tracked and studied about 9,000 close contacts of the COVID-19 virus. "Close contact" includes family contact (defined as people living under the same roof or eating together), colleagues, people in the hospital environment, and passengers in shared cars. The researchers monitored the infected person for at least 90 days after they tested positive for the COVID-19 virus to distinguish between asymptomatic patients and patients before the onset of symptoms.
Studies have shown that 89% of people identified as the primary case have mild or moderate symptoms, only 11% are asymptomatic, and no one has severe symptoms. Compared with other close contacts, family members of the original case and people who have been in contact with the original case for multiple or longer periods of time are more likely to contract the virus. However, regardless of these risk factors, if close contacts are in contact with the original case two days before or three days after the onset of symptoms, they are more likely to be infected with the COVID-19 virus.
Martinez said: "Our findings show that the timing of contact with the primary case is important for transmission, which further proves that rapid testing and isolation after someone feels unwell is a key step in controlling the epidemic."
In addition, compared with individuals with mild and moderate symptoms, asymptomatic primary individuals are less likely to spread the COVID-19 virus to close contacts, but if they spread, contacts are less likely to show obvious symptoms. Martinez said: "This study emphasizes the need for vaccination, which can reduce the severity of people infected with the COVID-19 virus."
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