Caixin
Mar 18, 2020 09:19 PM
SOCIETY & CULTURE

Scientists Map How Covid-19 Patient’s Immune System Defeated the Virus

Doctors examine a patient’s CT scan in Wuhan, Central China's Hubei province, the city at the epicenter of the country's coronavirus epidemic. Photo: Ding Gang/Caixin
Doctors examine a patient’s CT scan in Wuhan, Central China's Hubei province, the city at the epicenter of the country's coronavirus epidemic. Photo: Ding Gang/Caixin
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Australian scientists have mapped how a Covid-19 patient’s immune system fought off the disease, providing new insights that could help doctors direct treatment and researchers develop vaccines.

The team, from the Peter Doherty Institute in Melbourne, tested blood samples taken at four intervals in the course of treatment of a Wuhan woman with a mild-to-moderate infection.

The woman was one of Australia’s first Covid-19 cases.

The researchers found even though the disease is new, the otherwise healthy patient had mounted a “robust immune response across different cell types … similar to what we see in influenza,” said the corresponding author, immunologist Katherine Kedzierska of the University of Melbourne, in a statement from the research institute.

The study, published in the peer-reviewed journal Nature Medicine on Tuesday, is thought to be the first time broad immune responses to the disease were catalogued in detail.

It focuses on a 47-year-old woman from Wuhan — the city where the pandemic began — who was admitted to a hospital in Melbourne on an unspecified date, 11 days after she had arrived in Australia, and four days after she started to feel ill. She had classic coronavirus symptoms such as tiredness, sore throat, dry cough, chest pain and fever.

The woman had no contact with the South China Seafood Market — to which many of the first known cases of Covid-19 were linked — or with any known Covid-19 patients. She did not experience acute respiratory symptoms or require oxygen, and was discharged within a week of hospitalization, making hers a mild-to-moderate case on the spectrum of illness.

“We looked at the whole breadth of the immune response in this patient using the knowledge we have built over many years of looking at immune responses in patients hospitalized with influenza,” said study co-author Dr. Oanh Nguyen in the statement. “Three days after the patient was admitted, we saw large populations of several immune cells, which are often a tell-tale sign of recovery during seasonal influenza infection, so we predicted that the patient would recover in three days, which is what happened.”

“This is an incredible step forward in understanding what drives recovery of Covid-19,” Kedzierska said. “People can use our methods to understand the immune responses in larger Covid-19 cohorts, and also understand what’s lacking in those who have fatal outcomes.”

None of the researchers who worked on the paper were available for an interview, a spokesperson for the Doherty Institute told Caixin.

Dr. Emily Edwards, an immunologist at Australia’s Monash University who was not involved in the work, said the research was an important step, but she cautioned against drawing firm conclusions from a single case. “(The research is) fantastic in terms of being the first data that is out there on what the immune response is, but you have to be tentative about the assumptions and conclusions that you draw from a single-patient study.”

Understanding the immune response to Covid-19 is vital, because there are currently no proven drugs to treat it and no vaccines to prevent it. Doctors have no choice but to support patients — giving them symptomatic relief and breathing assistance where necessary — while they wait for the body’s immune system to eliminate the virus that causes it.

Exactly how the body fights Covid-19 has proved puzzling, with doctors recording scores of cases where patients appeared to “re-contract” it after recovering. Most experts say that’s highly unlikely, and that the phenomenon probably reflects lax hospital discharge criteria or testing failures. This month, a 36-year-old Wuhan man died of the disease just five days after being declared recovered and being discharged.

This research does not explain such cases, Edwards said, but it does demonstrate that the body mounts an immune response, and provides insights that will help clinicians determine how to treat patients.

“We have no evidence to suggest that individuals would not be (immune to) reinfection,” she added.

Edwards said similar research was now needed on a patient with a severe case. Such patients are thought to make up around 20% of cases. “We would expect that they would probably be slightly different (responses), and that the impact on the immune system might be more severe, which could be the reason why the individual could not clear the virus.”

While some researchers have posited that an over-activation of the immune system could cause some of the damage associated with Covid-19, Edwards said it was too early to say, but immunological and clinical data from more severe cases could give insights into whether that was the case.

Contact reporter Flynn Murphy (flynnmurphy@caixin.com) and editor Joshua Dummer (joshuadummer@caixin.com)

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