The longer the SARS-CoV-2 infection lasts, the higher the risk of Long Covid

A new study born from the Humanitas Covid Care research program, involving thousands of Humanitas healthcare workers and employees, suggests a mechanism behind the protection from Long Covid conferred by vaccines

Why do some people continue to experience COVID-19 symptoms even weeks and months after remission? In addition to already known risk factors – such as female sex and pre-existing allergies – a new study reveals the role of infection duration and could explain vaccines protection from Long Covid.

The study, published in the journal Clinical Infectious Diseases, was led by Prof. Maria Rescigno    – Vice Rector of Humanitas University and Group Leader of the Mucosal Immunology and Microbiota Lab at Humanitas Research Hospital – and was made possible thanks to the engagement of 4,534 Humanitas employees and healthcare workers, enrolled between March 2020 and April 2022 in the “Covid Care” monitoring program.

Vaccines protect against Long Covid

“Studying Long Covid is particularly challenging, not only because of the need to follow-up subjects for weeks and months after the end of the infection, but also because of the heterogeneity of its manifestations,” explains Maria Rescigno. “In fact, Long Covid is generically defined as the continuation of at least one Covid-19 symptom – including extreme fatigue, headache, cognitive fog, loss of sense of smell, cardiovascular and respiratory disorders – for at least 4 weeks after the first signs of Covid-19. At Humanitas, this study was possible thanks to the collaboration of all our colleagues and the hospital management team.”

On the protective role of vaccines, the new study confirms the evidence already presented in the first paper of the Covid Care program, published in Jama in July 2022: 3 doses protect not only from severe forms of the disease, but also from Long Covid. According to the data collected, out of 100 unvaccinated people, as many as 41 develop Long Covid, while among those fully vaccinated, only 16 out of every 100 people suffer from the disorder. In the 2022 study, however, a fundamental question remained unanswered: why?

The duration of symptoms predicts the risk of Long Covid

Data published in Clinical Infectious Diseases, based on a court of 1,293 healthcare workers, provide a potential explanation: the researchers found that the likelihood of contracting Long Covid increases as the duration of Covid-19 symptoms increases; duration that is substantially reduced in vaccinated people.

The study suggests a possible explanation for vaccines protection from Long Covid, an explanation that is coherent with what emerges from another recent study on Long Covid conducted in Humanitas by Marinos Kallikourdis and Gianluigi Condorelli. Explains Maria Rescigno: “The vaccine protects against Long Covid because it reduces the duration of infection. If the virus is present within the body for less time, there is less risk that the immune and inflammatory response triggered by its presence will become chronic and give rise to symptoms that persist in time.”