Catching the common cold could also protect against Covid, yet more research has suggested.
Ever since the start of the pandemic, experts have speculated other coronaviruses — which tend to cause runny noses and sore throats — could offer some cross-reactive immunity.
But new real-world evidence has uncovered the ‘clearest evidence’ yet that immunity induced by colds can help fight off Covid.
People with higher levels of T cells from other seasonal coronaviruses were less likely to get infected with SARS-CoV-2, the virus that causes Covid.
T cells are a key part of the immune system, and hunt down invading pathogens and stop them replicating within the body.
Imperial College London scientists studied 52 people who lived with someone who had tested positive for the virus. Half caught the virus, while the others managed to ward it off.
They took blood samples from the volunteers within days of being exposed to SARS-CoV-2, allowing researchers to determine their T cell levels.
Household contacts who did not test positive had ‘significantly higher levels’ of pre-existing coronavirus-fighting T cells, on average.
These T cells ‘targeted internal proteins within the SARS-CoV-2 virus rather than the spike protein to protect against infection’, the team said.
Professor Ajit Lalvani, one of the researchers, said: ‘Our study provides the clearest evidence to date that T cells induced by common cold coronaviruses play a protective role against SARS-CoV-2 infection.’
But experts warned people cannot rely on having had the common cold alone as protection against Covid and getting triple-jabbed remains ‘the best way to protect yourself’.
Imperial College London scientists took blood samples from 26 people who caught Covid from a positive household contact and 26 who warded off the virus to determine their T cell levels. They found two types of T cells – scientifically known as IL-2 (two left graphs) and pan-N-specific IL-2 (right two graphs) were on average higher among people who tested negative (blue) compared to those who tested positive (red)
But experts warned people cannot rely on having the common cold alone as protection against Covid and getting triple-jabbed remains ‘the best way to protect yourself’
The findings, published in the journal Nature Communications, showed the cells attacked the virus’ internal proteins, not the spike protein, which the virus uses to enter human cells.
Professor Lalvani said it could pave the way for a universal vaccine that protects against multiple variants.
Current Covid vaccines produce an antibody response that attacks the virus and stops it binding to and infecting cells, but this response wanes over time.
The jabs also trigger T cell immunity which is much longer-lasting. Once someone becomes infected, T cells stop an infection becoming much worse by protecting against hospitalisation and death.
Vaccines recognise the spike protein on the outside of the virus based on the original Wuhan strain. But as Covid mutates over time, vaccines risk becoming less effective.
WHAT DO WE KNOW ABOUT IMMUNITY AGAINST COVID?
People’s immunity against the coronavirus is boosted by vaccination or previous Covid infection.
Antibodies are the first line of defence against the virus and are important to stopping an infection in the first place.
They attack the virus and stop it binding to and infecting cells.
But if the virus is able to evade the antibody response, T cells kick in to identify and kill off infected cells, stopping them spreading further.
This means that antibodies can stop an infection, but if someone does get infected, T cells stop it from becoming much worse.
Studies and real-world data have shown that antibodies wane within months of being vaccinated or infected, while T cell protection against severe illness, hospitalisation and death is much longer lasting.
High vaccine uptake in the UK — with 83 per cent of over-12s double jabbed and 62 per cent boosted — along with high levels of previous infection — with 40 per cent of Britons thought to have had the virus — have weakened the link between infection, hospitalisation and death.
Omicron contains extensive mutations that have already cut the effectiveness of vaccines.
However, booster jabs have been found to boost protection against the variant to the equivalent of being double-jabbed against Delta.
But scientists fear that as Covid continues to spread and mutate, a version could emerge that jabs offer less protection against.
Professor Lalvani said the spike protein is under ‘intense immune pressure’ from the antibody-response triggered by vaccines, ‘which drives evolution of vaccine escape mutants’.
He added: ‘In contrast, the internal proteins targeted by the protective T cells we identified mutate much less.
‘Consequently, they are highly conserved between the various SARS-CoV-2 variants, including Omicron.
‘New vaccines that include these conserved, internal proteins would therefore induce broadly protective T cell responses that should protect against current and future SARS-CoV-2 variants.’
However, academics not involved in the small study warned it could be a ‘grave mistake’ to think anyone who previously had a cold caused by a coronavirus — which represent about one in 10 of all colds — is protected against Covid.
Dr Simon Clarke, a cellular microbiologist at the University of Reading, said the study adds to findings on how the immune system fights the virus.
But he said it ‘should not be over interpreted’. It is ‘unlikely’ the 150,000 people who’ve died within a month of testing positive for Covid ‘never had a cold caused by a coronavirus’, he said.
Dr Clarke said: ‘It could be a grave mistake to think that anyone who has recently had a cold is protected against Covid, as coronaviruses only account for 10 to 15 per cent of colds.
‘Similarly, there is no measurement of how much protection the reported effect gives people and a link is only hinted at, it has not been proven conclusively.’
Other studies uncovering a similar link have warned protection likely only lasts a short period of time because of how quickly immunity against the family of viruses that cause the cold last.