Although the genetic material of the novel coronavirus may still be detected in the respiratory or stool samples of Covid-19 patients for several weeks, no infectious virus particle was found beyond nine days of symptom onset, a new study says.
Antibodies were undetectable after 50 days in individuals who "develop modest neutralizing antibody titres after infection", while those patients who had more severe symptoms could continue to produce antibodies up to 60 days after infection, that study found.
The researchers assessed how much SARS-CoV-2 was detected between the mouth and the lungs at various time intervals.
Lead author author Dr. Muge Cevik of the University of St. Andrews, U.K. said in a statement that the new analysis "provides a clear explanation for why SARS-CoV-2 spreads more efficiently than SARS-CoV and MERS-CoV and is so much more hard to contain". Part of the reason researchers studied all three diseases was to determine why COVID-19 has spread more rapidly than the earlier diseases. "It provides a clear explanation for why SARS-CoV-2 spreads more efficiently than SARS-CoV and MERS-CoV and is so much more hard to contain", Cevik said.
There were 79 studies, with a total of 5,340 patients, with 58 studies in China, and 73 studies including hospitalized patients only.
Eighty-four delirious patients died in hospital, and scientists say delirium increases the risk of death by 24 per cent and likelihood of ICU admission by 67 per cent.
"Early case finding and isolation, and public education on the spectrum of illness and period of infectiousness are key to the effective containment of SARS-CoV-2", researchers from the University of Edinburgh, University of St Andrews, and Cotugno Hospital in Naples reported in The Lancet Microbe journal Friday. "We also need to raise public awareness about the range of symptoms linked with the disease, including mild symptoms that may occur earlier on in the course of the infection than those that are more prominent like cough or fever", Cevik said.
One study discovered that citizens who have recovered from Covid-19 hold powerful, "killer immune cells", regardless of if they present antibodies or not.
Researchers said the results are only relevant for the period of self-isolation for people with confirmed Covid-19, and do not apply to people simply quarantining after contact with someone infected.
The meta-analysis, which looked at published research on viral shedding, came to the conclusion that Covid patients shed the virus for a very long time, but are infectious for only for a short period.
The findings revealed that the average length of time of viral RNA shedding into the upper respiratory tract, lower respiratory tract, stool and serum were 17 days, 14.6 days, 17.2 days and 16.6 days, respectively.
Importantly, among 11 studies that attempted to isolate live virus, eight that attempted virus isolation in respiratory samples "successfully cultured viable virus within the first week of illness", but no live virus was isolated from respiratory samples after day 8 in three studies or after day 9 in two studies, Çevik and co-authors said.
Scientists had feared that those who developed only mild infections would be unlikely to have a strong immune response, but nearly all developed cells capable of creating new antibodies if they encountered the virus again.