Those of us who avoided COVID-19 over the past year may be somewhat surprised to learn there’s a good chance we’ve already been infected by at least one coronavirus.
They’re thought to be behind up to a third of all common colds. And intriguingly, evidence emerged last year that suggested people who were previously exposed to a common cold coronavirus might have some protection against COVID-19.
So could this cross-protection go the other way? Might the COVID-19 vaccines being rolled out now also cause a dip in seasonal coronaviruses?
Vaccines use parts of viruses or bacteria to train what’s called our adaptive immune system.
This part of our immune system protects us against specific microbes. It primarily involves molecules, called antibodies, that neutralise an invading pathogen.
In the case of COVID-19 vaccines, antibodies are made against the virus’s spike protein, which the virus uses to worm its way into our cells.
Your body needs quite a lot of energy to manufacture antibodies, so — ideally — vaccines also establish a few pathogen-specific immune cells called memory T cells and B cells that hang around long after the initial burst of antibodies has waned.
Might COVID vaccines protect against other coronavirus ?
If they do, it’s unlikely that antibodies generated by jabs will play a role, says Kirsty Short, a virologist at the University of Queensland.
A non-COVID-19 coronavirus would need spike proteins to be incredibly similar to those on SARS-CoV-2 for antibodies to recognise and destroy them.
Antibodies latch onto viruses like a lock and key. If the virus protein key is the wrong size or shape for the antibody lock, nothing happens.
But there is a chance that T cell immunity might step up against other coronaviruses. That’s because for those cells, the shape of a viral protein isn’t quite as important. They recognise smaller bits of viral proteins in the form of short chains of amino acids, or linear peptides.
“Some of those peptides are shared between seasonal coronaviruses and SARS-CoV-2,” Dr Short says.
And while measuring antibody levels from a blood test is relatively straightforward, it’s not as easy to find out what T cells get up to after a COVID-19 jab.
“In terms of T cell responses, they become a little bit more complex,” Dr Short says.
“The type of peptides that my T cells present to the immune system are going to be different to the type of peptides that your T cells will present.