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Medical researchers are getting clues about SARS-CoV-2, the virus that causes COVID-19, but there are big gaps in understanding our immune response: how well and for how long can we protect ourselves from infection in the future. .
That understanding is crucial in the effort to loosen lockout restrictions that will allow people to return to their workplaces and meet in public.
Some clues come from what we know about other viral infections, and from ongoing studies that trace those who had COVID-19 and recovered.
What is an infection?
Infection refers to the growth of microbes in the human host.
It is not the same as disease because an infection does not always harm.
What is known about the infection in COVID-19?
The incubation period between infection and the onset of symptoms appears to be about five to six days. It can vary from one to 14 days.
Symptoms are mild about 80 percent of the time, according to the World Health Organization.
Inpatients are admitted approximately one week after symptoms begin.
What about immunity?
Immunity is the ability to resist infection.
It can occur naturally when someone is infected and their body generates a successful immune response against him. To do this, the immune system creates general antibodies and specific protection against the particular infection, and retains a kind of memory to resist its return.
Or we can gain immunity by vaccinating with inactive or weakened forms of the virus to stimulate an immune response.
What do we not know about immunity to COVID-19?
Once the antibodies have completely removed the virus from someone’s system, the person recovers.
“In most cases, one would expect those antibodies to provide protection for a period of time,” World Health Organization chief of emergency Dr. Michael Ryan said last week. But we still don’t know the scope of protection for someone who has successfully fought this new coronavirus.
Immunologists say that in people who have symptoms, the antibodies start to appear after about a week and then peak after a week or two.
Even less is known about people who test positive for SARS-CoV-2 but never show symptoms.
Diagnostic nose or throat specimens used in COVID-19 testing centers and hospitals look for RNA, or genetic material, from the pandemic virus because it is faster than trying to grow the virus in an old-fashioned lab.
But it is only by cultivating the virus that scientists can tell whether it is viable or capable of causing disease.
Dr. Mark Loeb chairs the infectious disease division at McMaster University, where he studies viral infections like the flu (flu) and West Nile. Loeb said that scientists and doctors need to find more specific ways to measure immunity to COVID-19.
“The technical term for this is ‘protection correlates,'” Loeb said. “What kind of antibody level do you need to be protected? How long does it last? Those are important research questions.”
Why do scientists want to track immunity in populations?
Mona Nemer, Canada’s chief scientific adviser and member of the federal immunity working group COVID-19, said that knowing more about the immune response is also important in understanding what percentage of Canada’s population has been exposed to the virus.
“Right now, we are only evaluating people who show symptoms,” Nemer said.
We don’t really know how many people have been infected but are symptom-free, he said.
CLOCK | What it’s like to get an antibody test in the US USA
To perform these antibody tests, a person gives a blood sample with a puncture that is placed on a slide or cartridge. The cartridge is loaded into a device that indicates the presence or absence of two types of antibodies, called IgM and IgG, that indicate an immune response to COVID-19.
Daniel Altmann, an immunologist at Imperial College London’s Hammersmith Hospital, says that simple antibody testing yes or no is not enough.
“Would you give me the confidence that I tested positive that I was now ready to stand in line for a beer in a crowded pub, shoulder to shoulder with everyone else there? Not really, no” said Altmann, who co-wrote a comment in The Lancet medical journal titled “What Policymakers Should Know About COVID-19 Protective Immunity.”
In laboratories, researchers use a more sophisticated version of antibody tests than rapid tests that are evaluated for clinical use in Canada for so-called seroprevalence studies that will follow people in the general population over time to evaluate your antibody levels and see if symptoms develop
“By following people into a second wave, we will have a much better idea about all of these questions,” Loeb said.
What is collective immunity and why is it important?
Collective immunity occurs when enough people obtain protection against infection, either naturally or through vaccination, so that the majority of the population is resistant to the invasion and spread of a virus. When the majority of the population is resistant, that helps protect the most vulnerable.
But the proportion of the population that must be immune to achieve herd immunity differs by disease.
“We can rely on herd immunity, and herd immunity can be very weak and fragile,” Altmann said of the pandemic. “We can all be sitting around waiting for a new infection.”
CLOCK | Immunity after recovery:
