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Second Dose of Vaccine Substantially Lowers Risk of Long COVID-19

Although the risk of contracting COVID-19 remains low post full vaccination, investigators found there was a 49% less risk with developing long COVID.

Investigators found for those people who had second doses of the COVID-19 vaccines, there was a 49% less risk associated with Long COVID should they contract a COVID-19 infection.

"In terms of the burden of Long COVID, it's good news that our research has found that having a double vaccination significantly reduces the risk of both catching the virus and if you do, developing long standing symptoms,” study researcher Dr Claire Steves from King's College London said: However, among our frail, older adults and those living in deprived areas the risk is still significant and they should be urgently prioritized for second and booster vaccinations."

The study was published in The Lancet Infectious Diseases.

They analyzed data from participants logging their symptoms, tests and vaccines on the UK ZOE COVID Symptom Study app. The study period was between December 8, 2020 and July 4, 2021 and included 1,240,009 (for the first dose) and 971,504 (second dose) vaccinated United Kingdom adults. The research team assessed a range of factors, including age, frailty and areas of deprivation and compared that with post-vaccination infection.

"Study app users reported a first vaccine dose, of whom 6030 (0·5%) subsequently tested positive for SARS-CoV-2 (cases 1), and 971 504 reported a second dose, of whom 2370 (0·2%) subsequently tested positive for SARS-CoV-2 (cases 2). In the risk factor analysis, frailty was associated with post-vaccination infection in older adults (≥60 years) after their first vaccine dose (odds ratio [OR] 1·93, 95% CI 1·50–2·48; p<0·0001), and individuals living in highly deprived areas had increased odds of post-vaccination infection following their first vaccine dose (OR 1·11, 95% CI 1·01–1·23; p=0·039)," the investigators wrote in the study. "Individuals without obesity (BMI <30 kg/m2) had lower odds of infection following their first vaccine dose (OR 0·84, 95% CI 0·75–0·94; p=0·0030)."

There were also fewer hospitalizations (73% less likely) and lower burden of acute symptoms (31% less likely) among those fully vaccinated. The nature of the most common symptoms were similar to unvaccinated adults including anosmia, cough, fever, headaches, and fatigue. All these symptoms were milder and less frequently reported by people who were vaccinated, and they were half as likely to get multiple symptoms in the first week of illness. Sneezing was the only symptom which was more commonly reported in vaccinated people with COVID-19.

“Vaccinations are massively reducing the chances of people getting Long COVID in two ways,” Tim Spector, professor, King’s College London and lead investigator of ZOE COVID Study said. “Firstly, by reducing the risk of any symptoms by 8 to 10 fold and then by halving the chances of any infection turning into Long COVID, if it does happen. Whatever the duration of symptoms we are seeing that infections after two vaccinations are also much milder, so vaccines are really changing the disease and for the better. We are encouraging people to get their 2nd jab as soon as they can.”