You’re most contagious during first 5 days of coronavirus infection, study says
A person is the most contagious during the first five days of their coronavirus infection, a new study says, highlighting the importance of immediate self-isolation after potential exposure.
This is because the amount of virus, or viral load, peaks right when symptoms begin.
Researchers from the U.K. reviewed 98 studies that included at least five patients, mostly hospitalized, with three human coronaviruses — severe acute respiratory syndrome (SARS-CoV), Middle East respiratory syndrome (MERS-CoV) and SARS-CoV-2, the virus that causes COVID-19 — published in the last 17 years.
Seventy-nine of those studies focused on COVID-19.
The meta-analysis found that no live SARS-CoV-2, or virus that can cause infection, was found after nine days since symptoms started.
The researchers say their finding is “in line” with current recommendations set by many countries to self-isolate for at least 10 days after exposure, according to a news release on their study published Thursday in the journal The Lancet Microbe.
In contrast, the viral load for severe acute respiratory syndrome peaks between 10-14 days and between seven to 10 days for Middle East respiratory syndrome, both of which have genetic material similar to that of the novel coronavirus.
Because the coronavirus’ viral load peaks within the first five days, study lead author Dr. Muge Cevik said the research “provides a clear explanation for why SARS-CoV-2 spreads more efficiently than SARS-CoV and MERS-CoV and is so much more difficult to contain.”
“Our findings are in line with contact tracing studies which suggest the majority of viral transmission events occur very early… indicating the importance of self-isolation immediately after symptoms start,” Cevik, an infectious diseases lecturer at the University of St Andrews in Scotland, said in the release.
Existing research says that people with COVID-19 may be contagious anywhere between two to three days before symptoms surface, and that they may be most likely to spread the virus during the 48 hours before exhibiting symptoms, Harvard Medical School experts say.
The new study’s team also learned that people with COVID-19 who don’t show symptoms may clear the virus from their bodies faster than people who do experience symptoms. This suggests asymptomatic individuals may be just as contagious at the beginning of infection, but for a shorter period than symptomatic people, Cevik said.
“However, at this stage, there are limited data available on the shedding of infectious virus in asymptomatic individuals to inform any policy change on quarantine duration in the absence of testing,” he added.
The researchers note that many of the hospitalized patients included in the studies they reviewed received treatments that may have affected the course of their infection.
That’s why the findings may not apply to people with mild COVID-19 cases, “although these results suggest those with milder cases may clear the virus faster from their body,” study senior author Dr. Antonia Ho said in the release.
This story was originally published November 20, 2020 at 11:21 AM with the headline "You’re most contagious during first 5 days of coronavirus infection, study says."
