Being vaccinated against the SARS-CoV-2 virus halves people's risk of developing long COVID, according to the largest study of its kind.
The research, published in the journal JAMA Internal Medicine, reveals the risk factors associated with developing the long-term symptoms of Covid-19.
The study, which includes more than 860,000 patients also found that overweight people, women, smokers and those over the age of 40 are more likely to suffer from long COVID.
Researchers from the University of East Anglia (UEA) in the UK found that co-morbidities such as asthma, COPD, type 2 diabetes, coronary heart disease, immunosuppression, anxiety and depression are also associated with increased risk of long Covid.
Patients who are hospitalised during their acute COVID-19 infection are also more likely to experience long Covid.
"Long COVID is a complex condition that develops during or after having COVID, and it is classified as such when symptoms continue for more than 12 weeks," said Professor Vassilios Vassiliou, from UEA and Norwich University Hospital.
"Breathlessness, a cough, heart palpitations, headaches, and severe fatigue are among the most prevalent symptoms. Other symptoms may include chest pain or tightness, brain fog, insomnia, dizziness, joint pain, depression and anxiety, tinnitus, loss of appetite, headaches, and changes to sense of smell or taste," Vassiliou said.
The researchers wanted to find out what factors might make people more or less susceptible to developing long Covid.
They looked at data from 41 studies around the world, involving a total of 860,783 patients, to investigate the risk factors for developing long Covid.
"We found that female sex, older age, increased BMI and smoking are associated with an increased risk of long COVID," Vassiliou said.
"In addition, co-morbidities such as asthma, COPD, type 2 diabetes, coronary heart disease, immunosuppression, anxiety and depression are also associated with increased risk," the researcher said.
The study also shows that severe illness during the acute phase as reflected by the need for hospitalisation or admission to an intensive care unit, is also associated with the development of long Covid.
People who had been vaccinated had significantly less risk—almost half—of developing long Covid compared to unvaccinated participants.
"These findings are important because they enable us to better understand who may develop long Covid and also advocate for the benefit of vaccination," Vassiliou added.