Immunity to coronavirus could last for months, if not years, scientists find

Modesto Morganelli
Novembre 20, 2020

New research suggests that infectiousness peaks early in COVID-19 patients, highlighting the need to quickly identify and isolate cases before the virus spreads.

"The really good news is that people who are infected are very unlikely to become sick again for at least six months", one of the leading authors in the study, immunologist Michel Nussenzweig said.

"This is the first systematic review and meta-analysis that has comprehensively examined and compared viral load and shedding for these three human coronaviruses. 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", said lead author, Dr Muge Cevik, of the University of St Andrews, UK.

While the evidence so far on COVID-19 shows a pattern of nine days of infectiousness, researchers did not offer a suggestion as to how long quarantine periods should last, since their study only looked at confirmed cases and not individuals who may have been exposed.

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.

In the United Kingdom, officials say people must isolate immediately and for at least 10 days if they have any symptoms of coronavirus.

Patients suffering from Covid-19 are most infectious during their first week of illness, and therefore, it is important to isolate them early, researchers from the United Kingdom and Italy have said.

How infectious individuals are depends on many factors, including how much viable virus (essentially, virus that is able to replicate) they are carrying and the amount of virus they have in their bodies.

From these studies, the authors 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.

Citing the limitations of the research, the scientists said numerous patients across the different studies included in the analysis were hospitalised and received a range of treatments that may affect the course of their infection.

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. Asymptomatic infection may clear the virus faster, the researchers said, suggesting that those without symptoms may be as infectious as those with symptoms at the beginning of infection, but may remain so for a shorter period.

Limitations to the data, the team noted, included that the patients were on a wide range of treatments, which may have "modified the shedding dynamics", and the substantial heterogeneity in the study populations, follow-up, and management approaches.

The viral load in the upper respiratory tract - which is a key indicator of how likely a person is to spread the virus when they cough, sneeze or talk loudly - peaked in the first week of symptom onset, the researchers said.

While the study is yet to be peer-reviewed, initial reports suggest that the immune pathology of COVID recovered patients is "well-equipped" to recognize and fight off any virus upon exposure in the future.

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