People who have already had Covid-19 are twice as likely to suffer side effects from the vaccine, according to a symptom app.
Data collected through the ZOE Covid Symptom app found that mild post-jab symptoms are 33 per cent more likely among people who have already caught the virus.
By comparison, the likelihood of side effects among those who haven’t had the virus falls to just 19 per cent.
Common mild symptoms
The ZOE app has reported that a third of people previously infected with Covid-19 experienced at least one whole body side effect seven days after vaccination.
Around 37 per cent reported some side effects after the jab, including pain or swelling near the site of the infection after the first dose, with this rising to 45 per cent after the second dose.
Results found that the most common mild effects experienced were fatigue (nine per cent, headache (eight per cent) and chills or shivers (four per scent).
Most of these symptoms appeared in the first two days after vaccination, while only three per cent reported any side effects beyond three days.
The figures, which are based on a sub-sample of almost 40,000 vaccine doses, show that 14 per cent of people reported at least one whole body side effect within seven days from the first dose, compared to 22 per cent from the second, possibly indicating a stronger immune response after another dose.
The data also found that 13 per cent of vaccinated men, and 19 per cent of vaccinated women, reported at least one systemic side effect within seven days. Under 55s were more likely to experience whole body side effects than those who are older.
Increased immune response
Covid-19 vaccines work by using a harmless version or component of the virus to trigger an immune response, meaning the body is able to fight it off if it becomes infected.
This response can cause some mild symptoms, similar to those experienced when the body is fighting off a real infection, such as headaches, fever, chills, tiredness and muscle aches or pains.
A stronger response may indicate evidence of an increased immune response.
Tim Spector OBE, lead scientist on the ZOE Covid Symptom Study app and Professor of Genetic Epidemiology at King’s College London, said the results were positive.
He said: “This data set is a unique look at those who have been vaccinated in the real world outside trials, and so far the post vaccine effects we see are mild and in the minority of people.
"It’s interesting to see that those with previous Covid are more likely to experience these mild after effects than naive subjects.
"This could be good news, as a larger response like this suggests that those getting a first dose after having had Covid are generating a stronger immune reaction and may get greater protection from just a single shot of the vaccine.
"We are urging as many people as possible to download the ZOE app and log their vaccines with us, so that we can independently monitor how we all react differently and how the vaccines impact the overall pandemic.”