Why some people don’t get Covid-19, even if they live with an infected person

Why some people don’t get Covid-19, even if they live with an infected person
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A new study, published on Monday in the scientific journal ‘Nature,’ shows why some people do not get Covid-19 even if they live with someone who is infected with the coronavirus.

The study, led by Imperial College London researchers, started in September 2020 when only a minority of people in the UK had been infected with the coronavirus and followed 52 people who were living with someone who had tested positive.

“Being exposed to the SARS-CoV-2 virus doesn’t always result in infection, and we’ve been keen to understand why,” said Dr Rhia Kundu, first author of the study, from Imperial’s National Heart & Lung Institute. “We found that high levels of pre-existing T cells – created by the body when infected with other human coronaviruses like the common cold – can protect against Covid-19 infection.”

Participants did PCR tests at the start of the study, as well as four and seven days later to determine if they had developed an infection. Blood samples were taken within one to six days of being exposed to the virus. This allowed the researchers to analyse the levels of pre-existing T cells induced by previous common cold infections.

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The researchers found that the number of T cells in the 26 people who did not become infected was significantly higher than in the 26 who eventually did become infected after exposure.

From this, the scientists concluded that T cells had been generated by a previous infection with another coronavirus – such as a common cold virus – and effectively protected people from infection with Covid-19. These T cells targeted internal proteins within the SARS-CoV-2 virus to protect against infection, rather than the spike protein on its surface – which is how the vaccines work.

The study has been peer-reviewed with the scientists involved calling it “an important discovery”. They also warn that this is only one form of protection and that should should not be relied on by itself. “The best way to protect yourself against Covid-19 is to be fully vaccinated, including getting your booster dose.”

A blueprint for a universal vaccine

The researchers say that their findings provide “a blueprint for a second-generation, universal vaccine” that could prevent infection from current and future coronavirus variants, including Omicron.

“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,” said Professor Ajit Lalvani, senior author of the study and Director of the NIHR Respiratory Infections Health Protection Research Unit at Imperial.

“These T cells provide protection by attacking proteins within the virus, rather than the spike protein on its surface,” he added.

“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.”

In Belgium, KU Leuven virologist Johan Neyts called the study “interesting”, adding that the study had the potential for the “development of second-generation vaccines that are less variant of concern (VOC) dependent.”

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