Super-spreader events are key driver in Covid-19 pandemic

Henrietta Strickland
November 20, 2020

Immunity to coronavirus lasts at least eight months and may even continue for years, new research has suggested.

Meanwhile, inactive viral RNA fragments were still found in nose and throat samples on average up to 17 days after symptoms started.

Dr Muge Cevik, of the University of St Andrews, told the BBC that the findings showed people were most infectious very early on, in line with other studies involving contact tracing.

However, the genetic material of the coronavirus can be detected for several weeks in both respiratory and stool samples, but it is not believed to be infectious.

The highest COVID-19 viral load was detected early in the course of the disease - at the time symptoms begin, or before day five of symptoms. Part of the reason researchers studied all three diseases was to determine why COVID-19 has spread more rapidly than the earlier diseases.

In contrast, the viral loads of SARS and MERS peaked at 10-14 days and seven to 10 days after symptom onset respectively, explaining why transmission of these viruses can be effectively reduced by immediate identification, isolation and quarantine of people who show symptoms.

However, in a striking piece of information which throws new light at the situation, a team of researchers from Howard Hughes Medical Institute, Rockefeller University, New York, have found that rather than depleting entirely, the virus-fighting antibodies become more potent and capable of fighting any mutations and virulent strains of SARS-COV-2.

The study, published in The Lancet Microbe, specifically looked at people infected with COVID-19 and mainly those who were admitted to hospital. From these studies, the scientists calculated the average length of viral RNA shedding and examined the changes in viral load and the success of isolating the live virus from different samples collected throughout an infection.

Understanding when patients are most likely to be infectious is important for informing effective public health measures to control the spread of the virus.

The maximum duration of viral shedding was 83 days in the upper respiratory tract, 59 days in the lower respiratory tract, 126 days in stool samples, and 60 days in serum samples.

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.

"Several studies have found that individuals with asymptomatic infection may clear the virus faster, suggesting that those without symptoms may be as infectious as those with symptoms at the beginning of infection, but may be infectious for a shorter period".

The US-wide study looked at 817 older patients who tested positive for the coronavirus, 226 (28 per cent) of whom were diagnosed with delirium.

It also looked at isolation of the live virus - a stronger indicator of a person's infectiousness. "Therefore, our findings may not apply to people with milder infection although these results suggest those with milder cases may clear the virus faster from their body", said study senior author Antonia Ho of MRC-University of Glasgow Centre for Virus Research in the UK.

Other reports by Click Lancashire

Discuss This Article