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Why are some people protected from Covid-19 without having contracted the disease?

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New research suggests that exposure to other coronaviruses that cause the common cold could help develop antibodies against the SARS-CoV-2 virus

After months of uncertainty and grim headlines, some scientists are hesitantly recognizing what could be good news. During the first weeks of the Covid-19 pandemic, it was estimated that around 60% of the population would need to be exposed to the coronavirus to achieve herd immunity, which occurs when a high percentage of the community is immune to a disease.

large-scale antibody study in Spain found that around 5% of the population had contracted the coronavirus, with significant differences between the regions – in the Soria province, the figure was more than 14%, compared to 1.2% in Cádiz. The hope of achieving herd immunity seemed like a long shot. But as time passed, a growing amount of research began to suggest that more people are protected against the coronavirus, or at least its most serious versions, than the antibody studies indicated. Experts, however, do not want this news to be used as an excuse for the relaxation of coronavirus safety measures.

A health worker in Seville
PACO PUENTES / EL PAIS A health worker performs a PCR test in Seville

When there is an infection from a virus of the same family there could be a cross-reaction and the immune system could develop antibodies similar to the ones that neutralized the other virus

JUAN PABLO HORCAJADA, THE HEAD OF INFECTIOUS DISEASES AT MAR HOSPITAL

“We have been living with coronaviruses for a very long time. Most of them cause minor respiratory problems [like the common cold], while others are more serious, like SARS and MERS,” explains Juan Pablo Horcajada, the head of infectious diseases at the Mar Hospital in Barcelona. Four viruses in the coronavirus family cause around 25% of colds, and “it is well known that when there is an infection from a virus of the same family there could be a cross-reaction and the immune system could develop antibodies similar to the ones that neutralized the other virus,” he explains. “What we don’t know yet is if these antibodies can offer protection and if so, to what extent.”

A study recently published in the journal Science estimated that at least 20% or perhaps up to 50% of people who have never contracted SARS-CoV-2 have some kind of cellular protection against the disease. It is likely this has been generated by previous contact with one of the coronaviruses that cause colds. The research, however, has been done on cell samples and the hypothesis still needs to be tested out in real situations and on real people. For now, the authors of the study, researchers from La Jolla Institute for Immunology in the United States, acknowledge that it is “very speculative” to link the better prognosis of some Covid-19 patients with their previous exposure to the coronaviruses that cause the common cold.

Similar research from other groups has found the presence of protective T cells, the white blood cells that destroy infected cells in the body, in between 40% and 81% of samples. “This would explain the behavior of the pandemic in the last few weeks,” says Manel Juan, the head of immunology at Clínic hospital in Barcelona. “Although there is concern about the rise in cases, we are not seeing a repeat of the situation in March [when there were hundreds of daily deaths and hospitalizations] and this could be because a greater percentage of people are protected than is reflected in the antibody tests.”

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Source: El País

Original publication 12 August, 2020

Posted on NatCorn 3rd September 2020

Reference to an article does not infer endorsement of any views expressed.

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