Your immune system is like your own personal army: a vast network of cells, tissues and organs that coordinate your body's defences against illness and disease.

Yet how the immune system responds to coronavirus — and whether it mountsanylasting defence — is one of the biggest unknowns and most urgent questions facing researchers and health authorities right now.

"Like most other viruses, we're going to mount an immune response and in the short term that should mean that we're protected [from reinfection]," said Larisa Labzin, an immunologist from the University of Queensland.

"What we don't understand yet is exactly what that protection is, and how long it's going to last."

With less than four months of data — the outbreak only emerged in late 2019 — questions about immunity, especially in the long term, are difficult to answer.

Here's what we know so far.

How your body mounts a response

When your body detects an foreign invader like SARS-CoV-2, the new coronavirus that causes COVID-19, your immune system quickly triggers a series of responses to try to identify and remove it.

The first line of defence is what's known as the innate immune response, which is effectively "an amping up" of the immune system, said Dr Labzin.

"We tend to think of it as the non-specific response ... able to respond to anything that's invading and presenting a danger to the body," Dr Labzin said.

The innate immune response usually helps to slow down the infection before the adaptive immune response kicks in, which consists of antibodies made by B-cells and antiviral cell-killing T-cells.

Armed with more information about the infection — including the unique proteins found on the virus's surface called antigens — the body produces T-cells that go in search of infected cells and kill them.

Meanwhile, B-cells produce special proteins called antibodies which latch onto antigens like a lock and key. The first type of antibody to appear is called immunoglobulin M, or IgM.

To target and destroy the infection, the immune system refines this antibody into a second type called immunoglobulin G, or IgG, which can specifically recognise and neutralise the virus, and stop it entering new cells.

It typically takes a week or two for these antibodies to appear.

"As the immune system and those B-cells receive more information ... they can make a really specific response, and produce strong, protective antibodies against the virus," Dr Labzin said.

After your body has cleared the virus infection, a subset of antibodies and memory cells stick around — sometimes for years — ready to protect you if you encounter the same virus again.

What we know about COVID-19 immunity

Infection with COVID-19 activates your immune system, but some people will mount a better immune response than others,said virologist Bill Rawlinson.

"There have been papers looking at antibody [response] and other forms of immunity and we know that both types of antibody — the IgG type and IgM type — come up in a couple of weeks," said Professor Rawlinson from the University of New South Wales.

This response, it may be assumed, will offer some protection against the virus in the short- to medium-term. But it's too early to say how long that immunity will last.

"What you might do is look at the other four coronaviruses … that cause the common cold every year," Professor Rawlinson said.

"We know that [this immunity] lasts for sort of months to years, so we could expect that SARS-CoV-2 immunity would not be forever."

Some viruses, such as polio and measles, generate antibodies that can provide lifelong immunity. For others it may be just a few years, as is seen in Severe Acute Respiratory Syndrome (SARS).

"We think [COVID-19] is likely to be similar, because the virus is so similar."

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