One of the biggest questions facing health authorities around the world is whether or not an individual develops immunity to COVID-19 following infection. Whilst it is thought that the presence of antibodies to the SARS-CoV-2 virus could provide some protection, it is still not fully understood to what extent. We spoke to Dr Robert Norton, Director of Microbiology and Pathology at Townsville Hospital, to understand more about immunity and how it could apply to COVID-19.

“Immunity is the ability of an individual to withstand or to avoid infection. Our first line of defence against infection is our innate immune system which consists of physical, chemical and cellular defences against pathogens. This response is triggered by anything that the body recognises as foreign and is not specific to a particular pathogen. The innate immune response has no memory and therefore does not give long-lasting immunity.

“In most people, this innate response slows the spread of infection, allowing the ‘adaptive’ immune system to come into play. This is when the body recognises a specific antigen that it has encountered previously and then initiates the corresponding immune response. Adaptive immunity is acquired through natural infection or through vaccination, however it is important to note that natural immunity usually comes at a human cost.”

As COVID-19 is a new disease, there is no existing immunity within the community. This has meant that the virus has been able to spread very widely, very quickly. Although most people with SARS-CoV-2 seem to produce antibodies, it is still unknown what is needed for an individual to be effectively protected by these antibodies from future reinfection.

“Because humans have not seen this virus before, we had not yet developed the antibodies required for immunity. As with many infectious diseases, it is likely that it is the body’s response to the virus which causes the greatest harm, rather than the virus itself. One of the defining features of COVID-19 is the excessive immune reaction that it can cause in some people. This ‘cytokine storm’ may be severe or life threatening and can lead to multiple organ failure. We are not sure why this happens in some people and not in others but there are some theories – it is probably genetic.

“It is still unclear whether having a strong response to the virus will leave you any better off in the long run, but the hope is that a recovered patient has developed enough COVID-19-specific antibodies to fight off a recurrent infection,” said Dr Norton.

Serology tests can be used to detect antibodies made by the patient in response to SARS-COV-2 however it is important that these tests are not used to diagnose acute infection. If positive results from these IgG/IgM tests are found to predict immunity to COVID-19 then the testing devices could potentially be used to establish that it is safe for individuals to be exposed to persons with COVID-19, and/or that they are unlikely to pose an exposure risk to others. Until more data is available, the significance of test results at this time is not yet certain.

“These serology tests may be useful in the long term to tell us how many people were infected and what happens to these people, because it is likely that COVID-19 will come back or will continue for quite a while. It is therefore important to know once you have had COVID-19, whether or not you can get it again or whether infection provides protection. That is one of the questions we do not know.

“We also do not know if there will be any future strains of COVID-19 or if this is a one off in the human race. Influenza, for example, has many strains and getting infected with one strain does not necessarily provide immunity to another. We therefore do not know if a vaccine designed against this particular strain of COVID-19 will be effective against future strains. It is possible that it will and that is what we are hoping,” said Dr Norton.