What we know about immunity to coronaviruses

A review examining findings from more than 40 studies on coronavirus immunity suggests that SARS-CoV-2 could become the fifth seasonal coronavirus, with epidemics of the virus occurring over the next several years.

Written by UK virologists and published in the Journal of General Virology (JGV), the review discusses existing knowledge about immune responses to SARS-CoV-2 and other coronaviruses and how this could be used to inform virus control strategies. Available scientific evidence is collated in key areas, including how long immunity to coronaviruses lasts and the prospect of antibody testing.

Review authors Professor Paul Kellam and Professor Wendy Barclay from Imperial College London examined what is currently known about immunity to coronaviruses, including SARS, MERS and the four strains of seasonal coronaviruses that circulate in humans every winter.

“SARS-CoV-2 is a new virus in humans and because of this we are having to learn quickly many of its basic properties,” Professor Kellam said.

“In the absence of such data right now, we can try to make predictions about the immune response to SARS-CoV-2 by re-examining what we know about the two epidemic coronaviruses of humans, SARS and MERS, and the four seasonal human coronavirus[es].

“We need to be cautious about inferring too much, but it is a good place to start,” he said.

“We do not really know what happens on the pathway of a new coronavirus in humans becoming an endemic seasonal infection, but it could be that when the four seasonal coronaviruses first jumped from animals into humans they were much like SARS-CoV-2 in their transmission and pathogenesis.

“Over time, as population immunity to the seasonal coronavirus became widespread, the amount of severe disease probably declines. However, seasonal coronavirus can still cause pneumonia in some people,” Professor Kellam said.

Several factors, including disease severity, influence how long antibody protection lasts against SARS and MERS. Studies have shown that antibody protection decreases over time. For seasonal coronaviruses where disease is mild, there have been reports of reinfection after as little as 80 days.

“We need to find out many things about SARS-CoV-2 immunity, such as how good is the immune response and how long does it last?. We also need to understand if people with mild or asymptomatic infections develop a strong or weak immune response and what measurable properties of immunity predict protection from infection,” Professor Kellam said.

“When we know more about these things, we will be better able to understand how SARS-CoV-2 infections will continue over time. However, vaccines are not infections; therefore, it is likely that some of the vaccine candidates will be better at inducing long-lasting immunity and protection from infection.”

Antibody testing

The review also looked at currently available antibody tests for SARS-CoV-2, explaining the differences between these tests, their accuracy and their limitations. Knowing the level of immunity to SARS-CoV-2 in the population could be key in controlling the spread of disease and understanding how many people are at risk of infection.

JGV Deputy Editor-in-Chief Dr Alain Kohl said, “Understanding immune responses to these viruses is on many people’s minds — from the public hearing about vaccines, testing and antibodies, to policymakers and scientists working on or with an interest in the current pandemic.”

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