One in four people experiences mild, short-lived systemic side effects after receiving either the COVID-19 preventive by Pfizer or AstraZeneca vaccine — known as Covishield in India — with headache, fatigue, and tenderness the most common symptoms, according to a study published in The Lancet Infectious Diseases journal. The researchers from King’s College London in the UK also found that most systemic side effects — meaning side effects excluding where the injection took place — peaked within the first 24 hours following vaccination and usually lasted 1-2 days.
Data analysis from the ZOE COVID Symptom Study app found much fewer side effects in the general population with both the Pfizer and AstraZeneca vaccines than reported in trials.
The study also reports a significant decrease of infection rates from 12 to 21 days after the first dose of the Pfizer (58 percent reduction) and AstraZeneca (39 percent reduction) vaccines compared to a control group. According to the study, the drop in infection at least 21 days after the first dose for Pfizer is 69 percent, and for AstraZeneca, 60 percent.
Systemic effects included headache, fatigue, chills and shiver, diarrhea, fever, arthralgia, myalgia, and nausea.
Local side effects — meaning side effects where the injection took place in the arm — included pain at the site of injection, swelling, tenderness, redness, itch, warmth, and swollen armpit glands.
“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 50’s who are most at risk of the infection,” said Professor Tim Spector, lead scientist on the ZOE COVID Symptom Study app and Professor at King’s College London.
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.
The study also found that side effects were more common among people under 55 years of age and women.
Participants who had a confirmed case of prior 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 known infection.
Those with a confirmed case of prior COVID-19 number were almost twice more likely to have side effects that affect the whole body after the first dose of the AstraZeneca vaccine.
The researchers said that people with prior known COVID-19 infection were also more likely to experience local side effects.
The researchers noted that in Phase III clinical trials of the Pfizer vaccine, the most common side effects were pain at the injection site (71-83 percent), fatigue (34-47 percent), and headache (25-42 percent).
However, the real-world analysis found less than 30 percent of users complained of injection site pain and less than 10 percent of fatigue and headache after the first dose, they said.
Similarly, in Phase III trials for the AstraZeneca vaccine, systemic side effects were found in 88 percent of younger participants (18-55 years) after the first dose. Still, the study found a significantly lower rate of 46.2 percent after the first dose.
“Our results support the after-effects safety of both vaccines with fewer side effects in the general population than reported in the Pfizer and AstraZeneca experimental trials and should help allay safety concerns of people willing to get vaccinated,” Spector added.