One in four people experiences mild, short-lived systemic side-effects after receiving either the Pfizer or AstraZeneca coronavirus vaccine, new research suggests.
Headache, fatigue and tenderness are the most common symptoms, with most effects peaking within 24 hours after vaccination, usually lasting one to two days, according to the study.
The paper, published in the Lancet Infectious Diseases, compared both jabs and investigated the prevalence of mild side-effects of the UK’s vaccination programme.
The analysis by researchers from King’s College London of data from the Zoe Covid Symptom Study app found fewer side-effects in the general population with both the Pfizer and AstraZeneca vaccines than reported in trials.
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% 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.”
The study also reports a decrease of infection rates from 12 to 21 days after the first dose of the Pfizer (58% reduction) and AstraZeneca (39% reduction) vaccines compared with a control group.
According to the research, the drop in infection at least 21 days after the first dose for Pfizer is 69% and 60% for AstraZeneca.
The analysis looked at the differences of reported side-effects from the first two vaccines to be offered in the UK.
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.
Overall, the study found that 25.4% of vaccinated people indicated suffering from one or more systemic side-effects, whereas 66.2% reported one or more local side-effects.
Around 13.5% of participants reported side-effects after their first Pfizer dose, 22% after the second Pfizer dose and 33.7% after the first AstraZeneca dose.
The most reported systemic side-effect was headache, with 7.8% of people reported suffering from headaches after the first Pfizer dose and 13.2% after the second Pfizer dose.
The research found more side-effects in those under the age of 55, and among women.
Participants who had previously had coronavirus were three times more likely to have side-effects affecting the whole body after receiving doses of the Pfizer vaccine than those without known infection.
They were almost twice as likely after the first dose of the AstraZeneca vaccine.
Those with prior known Covid-19 infection were also more likely to experience local effects.
A separate study by the University of Bristol, King’s College London and the NIHR Health Protection Unit in Emergency Preparedness and Response, found that the public’s preference for the AstraZeneca vaccine has declined since last month, and belief that it causes blood clots has increased.
Despite this, the research suggests that vaccine confidence is higher than it was towards the end of 2020, and there has been a big rise in the proportion of people who say they want to be vaccinated as soon as possible.
It is based on a survey of 4,896 UK adults aged 18 to 75, carried out between April 1 and April 16 2021.
According to the findings, 17% of the public now say they would prefer to have the AstraZeneca vaccine, if they had a choice – down from 24% towards the end of March.
And 23% of people now believe the AstraZeneca vaccine causes blood clots – up from 13% last month.
But the public are still most likely to say this claim is false (39%) or that they do not know whether it is true (38%).
Overall, 81% of people now say vaccines are safe, compared with 73% who said the same towards the end of 2020.