Headaches and fatigue were the most common symptoms reported by users of the Zoe Covid Symptom Study app with most effects peaking within 24 hours and usually lasting one to two days.
The side-effects study, published in the Lancet Infectious Diseases, compared both jabs and investigated the prevalence of mild side-effects in the UK’s vaccination programme.
The analysis by researchers from King’s College London found fewer side-effects in the general population with both the Pfizer and AstraZeneca vaccines than reported in trials.
Systemic effects – meaning side-effects excluding the injection site – included headache, fatigue, chills and shiver, diarrhoea, fever, arthralgia (joint pain), myalgia (muscle pain), and nausea.
Local side-effects – where the injection took place in the arm – included pain, swelling, tenderness, redness, itch, warmth and swollen armpit glands.
The data comes from 627,383 users of the Zoe Covid Symptom Study app who self-reported systemic and local effects within eight days of receiving one or two doses of the Pfizer vaccine or one dose of the AstraZeneca vaccine between December 8 and March 10.
Tim Spector, professor of genetic epidemiology at King’s College London and lead scientist on the Zoe Covid Symptom Study app, said: “The data should reassure many people that, in the real world, after-effects of the vaccine are usually mild and short-lived, especially in the over-50s, who are most at risk of the infection.
“Rates of new disease are at a new low in the UK, according to the Zoe app, due to a combination of social measures and vaccination, and we need to continue this successful strategy to cover the remaining population.”
He added: “The results also show up to 70 per cent protection after three weeks following a single dose, which is fantastic news for the country, especially as more people have now had their second jabs.”
