COVID-19 and immunity – Expert Briefing

The SMC led an online media briefing about the immune system, COVID-19 and what we know about whether people may develop immune responses after being ill.

Dr Nikki Moreland, senior lecturer in immunology, University of Auckland

The full briefing is available here.

A transcribed Q&A with Dr Moreland is below.

How does the immune system work when we are exposed to an infection?

“There’s a series of events that happen when we are exposed to infectious viruses. The first thing is we have this very rapid non-specific response. That’s what we call our innate immune response. So that’s really to try and slow that virus down initially and then over a period of days to weeks what happens other parts of our immune response kick in and primarily what happens is our body starts developing these things that we have all heard about called antibodies. The first antibodies that come on the scene and start binding and trying to block viruses are what are known as IgM antibodies. And then a little bit later the system response develops a little bit more and then we get our IgG antibodies. Alongside our antibody response, we also have our cellular immune response. So our cellular immune response is driven by a particular type of cells that we know as T cells. They work together with the antibodies to try and contain the infection.”

Why do we get some infections, like measles, only once but with others like cold and flu we can get sick multiple times?

“So there are a couple of different things that come into play there. One is the immune response itself. With some infections, we can develop a really long-lived immune response that does essentially protect us for a lifetime and for other viruses we need to tune the immune response so that we develop new antibodies on repeat exposures. But the other thing we need to consider in this is the actual microbe itself. So with things like influenza, the influenza strains differ from season to season and that’s why we don’t necessarily have life-long protection against influenza, because there’s a difference in the strains that we’re exposed to from year to year.”

What do we know about how the immune system responds to COVID-19? Is it likely people will be immune to catching it again?

“We don’t have that data yet, because coronavirus is such a new virus. We really only have data from people who have been infected from January this year and we’re only sitting in May. So it’s going to be quite some time before we have any clear idea about long-term immunity or protection from subsequent infections of coronavirus.

“What we do know from SARS, which is quite a closely-related virus that we saw in 2003, is that people who were infected with SARS there is evidence they are carrying antibodies for some years afterwards. So that gives us hope for COVID-19.”

We’ve seen talk about the use of so-called ‘immunity passports’ – do you think they are likely to be used?

“Right now, I think it’s far too early to be thinking about immunity passports. Until we have that data and that understanding about whether the presence of antibodies and immune response leads to protection from a subsequent infection then we can’t really say when someone is immune or not.”

What are antibody tests looking for and what can they tell us?

“Antibody tests are looking for specific antibodies (the IgM and the IgG) that are targeted to COVID-19. So these are the antibodies that a body would produce after someone has been infected with the virus. So the tests work by measuring the level of those antibodies in the blood.”

These tests are being developed on the fly. Are we starting to see information coming in that those are working and they are picking up those responses?

“It’s important to realise there are two different kinds of antibody tests. There are lab-based antibody tests and these are tests where someone would have blood taken from them at a medical facility. That blood then comes back to the lab and it’s analysed in the lab for the level of antibodies. And there are a lot of these tests being developed and we’re starting to see some quite good data come out on these tests in terms of their performance and accuracy.

“The other kinds of antibody tests that did receive a lot of attention some weeks ago are these rapid point-of-care antibody tests. They were talked about as something you might be able to do at home where you take a fingerprint of blood and you get a quick yes or no answer as to whether someone has COVID antibodies or not. Those tests have not really been properly assessed for accuracy. Now there’s been a refocus on getting the lab antibody tests as accurate and as validated as possible and scientists can use those to look at the accuracy of these point of care tests, but they’re a little way away yet.”

How would the lab-based test be used in places where there has been a lot of infection like New York, Spain or Italy. Will it point out if there have been more people infected beyond the ones that we know about?

“Those studies and that data gathering is now underway. There was the recent study that came out from Spain where they looked at health care workers and they used lab-based antibody tests to see if there were health care workers whose potential infections had been missed. They did this by looking at the presence of antibodies to COVID-19. Similarly in New York some of that work is underway. They’ve got a really high disease prevalence there so in a setting like that antibody tests could be useful to look at screening people that have been exposed to see if they have had a previous infection.”

How might antibody tests be used in New Zealand?

“New Zealand is a very different setting to New York and Italy. We’re in a very fortunate position at the moment. We’re a really low prevalence setting so overall we’ve had very few cases. So what that means right now is that widespread antibody testing is probably not a good use of resources and that’s because all tests have limitations. COVID antibody tests are no exception. Their predictive value of being able to identify someone who has truly been affected is around 99 per cent. Some are climbing a little bit higher than that. What that means is every 1 in 100 people (if you ran a test on 100 people) will be a false positive. They throw a false positive on a test for whatever reason and that’s the limitation of the test. So if we were to roll out that test in say a town of 10,000 people in New Zealand randomly, 100 people in that town would show a positive on a test but in fact, they’re false positives. So in a low prevalence setting like New Zealand where we’re kind of looking for needles in haystacks it would be virtually impossible to tell a true needle from a false needle with the current tests that are available.”

What work are you and your team currently focused on in this area?

“We have been establishing lab-based antibody tests and we’ve had a great collaboration with scientists and clinicians up and down the country to get this going. We have some lab-based antibody tests working to detect COVID antibodies.”

Are you looking at samples from New Zealand?

“So we have set up the tests using samples from patients that have been hospitalised with COVID-19. What we’re really doing is wanting to use antibody testing to understand the immune response to COVID-19. Right now in New Zealand, I don’t think there’s a place for wide antibody surveys at a population level just yet due to our low prevalence.”

How does this information feed into the work to develop a vaccine?

“Understanding the immune response and being able to accurately detect COVID antibodies will be absolutely central to developing vaccines. Because when you do a clinical trial for a vaccine what you want to know is that someone has developed antibodies to the vaccines and what you want to be able to do is then follow individuals over time to measure how long those antibodies persist for and to gauge whether a vaccine is providing longer-term protection.”

What does it mean that someone is immuno-compromised and how can they best be protected?

“When someone’s immune-compromised it means their ability to respond to a virus or microbe is limited. Some of the things we talked about at the beginning like innate immune responses and the antibodies and cellular responses are not as effective at developing a protective immune response to something new. So for viruses that we have vaccines for, the best way that we can protect those people and create a wall of protection around them is by having everyone vaccinated.  For a new virus like COVID-19 where we don’t have a vaccine the best way we can protect immune-compromised people in our population is to create that wall with physical distancing.”