New research looks at how immune system reacts to COVID-19 variants

Australian Red Cross Lifeblood

In a new study published in the journal PLOS Medicine, researchers from the University of Sydney looked at how the immune system responds to the novel coronavirus (COVID-19), revealing that those infected by early variants in 2020 produced sustained antibodies, however, these antibodies are not as effective against contemporary variants of the virus.

The research is one of the world's most comprehensive studies of the immune response against COVID-19 infection. It suggests vaccination is more effective than the body's natural immune response following infection and shows the need to invest in new vaccine designs to keep pace with emerging COVID-19 variants.

For the study, researchers analyzed the serum of 233 individuals diagnosed with COVID-19 over seven months and uncovered that the level of immunity over time is dependent on disease severity and the viral variant. They show that antibodies developed during the first wave had reduced effectiveness against six variants, including the main variants of concern in the United States, B.1.1.7 (Alpha), B.1.351 (Beta), B.1.617.2 (Delta), and P.1 (Gamma).

The serum of COVID-19 infected individuals was of interest as it is the part of our blood that contains crucial information about our immune system. Analysis of the serum made it possible to create a detailed timeline of the level of neutralising antibodies produced against COVID-19 infection, and to see if there was long-term immunity.

Neutralising antibodies are part of our immune system's frontline arsenal that is triggered during infection and vaccination. Their job is to shield cells that are usually the target of a pathogen (such as the SARS-CoV-2 virus which causes the COVID-19 disease) from being infected. The level of neutralising antibody response can be a defining feature of how effectively our body fights off illness.

Interestingly, a rare group of super responders was also identified as an exception. This group had a stable and robust level of antibodies across all COVID-19 variants. The researchers said this group could prove useful for investigating the potential of convalescent plasma, using blood from people who have recovered to treat others, which has so far proven ineffective against severe COVID-19 illness. In addition, key donors could be looked at closely and their antibodies cloned for future therapeutic use.

"What this work has shown us is that current observations about vaccines show they offer a much broader protection against COVID-19 and its variants than the body's natural immune response following infection, which is usually only protective against the variant of the virus that the person was infected with,” said Stuart Turville, PhD, co-senior author of the study, in a statement. “We, therefore, should not rely on the body's natural immune response to control this pandemic, but rather the broadly protective vaccines that are available."

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