Only 1 in 4 people experience mild systemic side effects from the COVID-19 vaccine

After receiving either the Pfizer vaccine or the AstraZeneca vaccine, 1 in 4 people experience mild, short-term systemic side effects, with headache, malaise, and tenderness being the most common symptoms. Most side effects peaked within the first 24 hours after vaccination and usually lasted 1-2 days.

Study published today Lancet infection Is the first large-scale study comparing two vaccines to investigate the prevalence of mild side effects in the UK vaccination program.

In the analysis of data from the ZOE COVID Symptom Study app by researchers at King’s College London, General population With both Pfizer and AstraZeneca vaccines than reported in the trial.

The study also reported a significant reduction in infection rates 12 to 21 days after the first dose of the Pfizer (58% reduction) and AstraZeneca (39% reduction) vaccines compared to the control group. At least 21 days after the first dose of Pfizer, the reduction in infection is 69% and that for AstraZeneca is 60%.

This large analysis examined the differences in side effects reported from the two vaccines currently distributed in the United Kingdom. Systemic effects (meaning side effects except where the injection was made) included headache, malaise, chills and tremors, diarrhea, fever, arthralgia, myalgia, and nausea. Local side effects (meaning side effects when the injection was given to the arm) included pain, swelling, tenderness, redness, itching, warmth, and swelling of the armpits at the injection site.

Data show 627,383 people from the ZOE COVID Symptom Study app who self-reported systemic and local effects within 8 days of receiving one or two doses of Pfizer or AstraZeneca vaccine between December 8 and March 10. From the user of.

Summary of findings:

• 25.4% of vaccinated people showed that they suffered from one or more systemic side effects (excluding the area where the injection was given), while 66.2% showed one or more local (excluding the area where the injection was given). Reported side effects of the injection site).
• 13.5% of participants reported side effects after the first Pfizer dose, 22.0% after the second Pfizer dose, and 33.7% after the first AstraZeneca dose.
• The most reported systemic side effect was headache. 7.8% reported suffering from headaches after the first dose of Pfizer, and 13.2% reported suffering from headaches after the second dose of Pfizer. 22.8% of those who received the first dose of the AstraZeneca vaccine reported headaches.
• The second reported systemic side effect was fatigue. 8.4% and 14.4% of participants reported fatigue after the first and second doses of the Pfizer vaccine, and 21.1% reported fatigue after the first dose of the AstraZeneca vaccine.
• The most common local side effects were tenderness: 57.2% and 50.9% after the first and second doses of the Pfizer vaccine, 49.3% after the first dose of the AstraZeneca vaccine.

Importantly, this study identifies that side effects are more common among people under the age of 55 and women.

In addition, participants with previously confirmed cases of COVID-19 were three times more likely to have systemic side effects after Pfizer vaccine administration than participants without known infections, and were initially administered. Later it was almost twice as likely. AstraZeneca vaccine. People with previously known COVID-19 infections 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%), malaise (34-47%), and headache (25-42%), but actual analysis Less than 30% of users complained of pain at the injection site, and less than 10% had fatigue and headache after the first dose. Similarly, in a phase III study of the AstraZeneca vaccine, systemic side effects were seen in 88% of young participants (18-55 years) after the first dose, compared with 46.2% after the first dose in this study. A significantly lower rate was seen.

Although the incidence of side effects was much lower than expected from clinical trials, post-vaccination infection rates were reassuring 2-3 weeks later, with the results of previous trials and recent data from the Israeli vaccination program. It was a match.

Tim Spector OBE, Principal Scientist of the ZOE COVID Symptom Study App and Professor of Genetic Epidemiology at King’s College London, said: vaccine It is usually mild and short-lived, especially in the 50s and older, who are at the highest risk of infection. According to the ZOE app, the combination of social measures and vaccination has resulted in a new low incidence of new diseases in the UK. This successful strategy needs to be continued to cover the rest of the population. “

“The results also show up to 70% protection 3 weeks after a single dose, which is great news for the country, especially now that more and more people are doing a second jab.”

Dr. Christina Menni, the first author of King’s College London’s work, said: Side effects It should help alleviate safety concerns of people seeking vaccination in the general population than reported in the Pfizer and AstraZeneca trials. ”