The study, published in Nature Communications, examined 52 individuals who had not yet been vaccinated but who lived with someone who had just caught the coronavirus.
Half of the people involved went on to contract the virus within the 28-day research period, while the remaining 50pc did not.
A third of the people who didn’t catch Covid were found to have high levels of specific memory immune cells in their blood.
These immune cells, called T-cells, were likely to have been created previously when the body fought off a similar virus such as the common cold.
The study concluded that participants who developed a “memory bank” of specific T-cells after catching a common cold were less likely to contract Covid.
However, experts say that it would be a “grave mistake” to rely on these defences alone, emphasising the importance of vaccines.
Dr Simon Clarke, at the University of Reading, said although this was a small-scale study, it contributed to the understanding of how our immune system fights Covid-19.
“These data should not be over-interpreted. It seems unlikely that everyone who has died or had a more serious infection, has never had a cold caused by a coronavirus,” he told BBC News.
“And it could be a grave mistake to think that anyone who has recently had a cold is protected against Covid-19, as coronaviruses only account for 10-15pc of colds.”
Professor Ajit Lalvani said vaccines were key to protection against Covid.
“Learning from what the body does right could help inform the design of new vaccines,” he said.
“Current vaccines specifically target spike proteins that sit on the outside of the virus, but those spike proteins can change with new variants.
“But the body's T-cells target internal virus proteins, which do not change as much from variant to variant, meaning vaccines harnessing the work of T-cells more closely could provide broader, longer-lasting protection against Covid,” he added.