New research from the UK is some of the first to examine the potential risk of experiencing lingering symptoms after a case of covid-19 in vaccinated people, a phenomenon often known as long covid. The study suggests that vaccinated people who become infected are half as likely to experience long-lasting symptoms than the unvaccinated. Importantly, this reduction in risk is in addition to the protection against any symptoms from covid-19 that vaccination already provides.
The data for this new research, published Wednesday in The Lancet Infectious Diseases, comes from the COVID Symptom Study: a long-running project that’s tried to keep track of the pandemic’s spread with a free mobile app, through which people in the UK are encouraged to report any covid-like symptoms they experience and other relevant details, including whether they’ve tested positive for the virus as well as their vaccination status. The app was launched in March 2020, and there are reportedly around 4.5 million unique users. In the UK, people have access to vaccines developed by Pfizer/BioNTech, Oxford/AstraZeneca, and Moderna.
The researchers compared the outcomes of around a million users who reported being partially and/or fully vaccinated to a control group of unvaccinated users. Up until July 2021, about 8,000 of these vaccinated individuals reported a confirmed breakthrough infection (less than 1% of the total sample), with only about 2,000 reporting an infection a week or more after the second dose.
Compared to the unvaccinated and infected, vaccinated people were significantly less likely to report needing hospitalisation, reported having no symptoms more often, and reported having less symptoms on average when they did get sick. Only about 5.2% of the fully vaccinated and infected reported experiencing any symptoms beyond 28 days, compared to 11.4% of the control group, indicating that the odds of having these longer-term symptoms were cut by 47%.
“Vaccinations are massively reducing the chances of people getting long covid in two ways. 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,” study author Tim Spector, a researcher at King’s College London and lead investigator of the project, said in a statement released by the university. “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.”
The study is one of the first to attempt measuring the possible prevalence of long covid in breakthrough infections. So it’s possible that this will not be the last word on how it often can happen. In July, for instance, a study of healthcare workers in Israel found that 19% of those with breakthrough infections had persistent symptoms for more than six weeks. Similarly, though, the odds of having any infection in the first place were low (about 2% in the group of 1,500 people who were regularly tested).
Studies of long covid in general have found varying rates of prevalence in survivors, ranging from 10% to 30%. These estimates are further complicated by the reality that some people can experience many of the symptoms closely linked to long covid, like mental and physical fatigue, after having other respiratory infections, while many people can have these symptoms for no clear reason at all.
While the exact numbers may be in flux, it does seem fair to say vaccines offer significant but not complete protection against the worrying possibility of long covid.