One in four people have mild, short-lived systemic side effects after receiving the Pfizer or AstraZeneca vaccine, with the most common symptoms being headache, fatigue and tenderness. Most side effects peaked within the first 24 hours after vaccination and usually lasted 1 to 2 days.
The study published today in the Lancet Infectious Diseases is the first large-scale study to compare the two vaccines and to investigate the prevalence of mild side effects from the UK vaccination program.
Analysis by researchers at King’s College London of data from the ZOE COVID Symptom Study app reassuringly found significantly fewer side effects in the general population with Pfizer and AstraZeneca vaccines than those reported in trials.
The study also reports a significant decrease in infection rates 12 to 21 days after the first dose of Pfizer (58% reduction) and AstraZeneca (39% reduction) vaccines compared to a control group. The reduction in infection at least 21 days after the first dose of Pfizer is 69% and AstraZeneca 60%.
This large-scale review looked at the differences in reported side effects of the two vaccines currently distributed in the UK. Systemic effects – that is, side effects excluding the injection site – included headache, fatigue, chills and chills, diarrhea, fever, arthralgia, myalgia and nausea; while local side effects – that is, side effects where the injection took place in the arm – included pain at the injection site, swelling, tenderness, redness, itching, warmth and swelling of the armpits.
The data comes from 627,383 ZOE COVID Symptom Study users who self-reported systemic and local effects within eight days of receiving one or two doses of Pfizer vaccine or one dose of AstraZeneca vaccine between December 8 and March 10.
Summary of Findings:
- 25.4% of those vaccinated reported suffering from one or more systemic side effects (excluding the area where the injection took place), while 66.2% reported one or more local side effects ( at the injection site).
- 13.5% of participants reported side effects after their first dose of Pfizer, 22.0% after the second dose of Pfizer, and 33.7% after the first dose of AstraZeneca.
- The most reported systemic side effect was headache. 7.8% of people reported having a headache after the first dose of Pfizer and 13.2% after the second dose of Pfizer. 22.8% of people who received the first dose of AstraZeneca vaccine reported a headache.
- The second most reported systemic side effect was fatigue. 8.4% and 14.4% of participants reported fatigue after the first and second dose of Pfizer vaccine and 21.1% reported fatigue after their first dose of AstraZeneca vaccine.
- The most common local adverse reaction was sensitivity: 57.2% and 50.9% after the first and second dose of Pfizer vaccine and 49.3% after the first dose of AstraZeneca vaccine.
Importantly, this research identifies that side effects were more common in people under 55 and in women.
In addition, participants who had a previous confirmed case of COVID-19 were three times more likely to have side effects that affect the whole body after receiving doses of the Pfizer vaccine than those without a known infection and almost twice as likely. after the first dose of the vaccine. AstraZeneca vaccine. People who had previously had a known COVID-19 infection were also more likely to experience local effects.
In Phase III clinical trials of the Pfizer vaccine, the most common side effects were injection site pain (71-83%), fatigue (34-47%), and headache (25-42% ), but real-world analysis found that less than 30% of users complained of pain at the injection site and less than 10% of fatigue and headaches after the first dose. Likewise, in phase III trials for the AstraZeneca vaccine, systemic side effects were seen in 88% of younger participants (18 to 55 years old) after the first dose, but this study found a significantly lower rate of 46.2% after the first dose.
While rates of side effects were much lower than expected in clinical trials, post-vaccination infection rates were reassuring after two to three weeks and in line with previous trial results and recent data from the Israeli vaccination program. .
Professor Tim Spector OBE, ZOE COVID Symptom Study Principal Scientist and Professor of Genetic Epidemiology at King’s College London, said: “The data should reassure many that in the real world the effects Vaccine side effects are generally mild and short-lived, especially in those over 50 who are most at risk of infection. Rates of new diseases are at new low in UK according to ZOE app , due to a combination of social measures and vaccination and we must continue this successful strategy to cover the remaining population. “
“The results also show up to 70% protection after 3 weeks after a single dose, which is great news for the country, especially as more people have now had their second injection.”
Dr Cristina Menni, first author of the King’s College London study, said: “Our results support the safety of the side effects of both vaccines with fewer side effects in the general population than those reported in the Pfizer experimental trials. and AstraZeneca and should help ease concerns about the safety of people ready to be vaccinated. “
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Material provided by King’s College London. Note: Content can be changed for style and length.