Mild side effects most likely in 24 hrs after vaccination: Study

As vaccination against COVID runs across the world, questions related to its efficacy in preventing virus infection and side effects are also emerging to get clean out of it.

According to a report published in The Lancet Infectious Diseases Journal, one out of four people, who received Pfizer or AstraZeneca vaccine, is most likely to experience headache, fatigue and tenderness in the first 24 hours after the vaccination.

Most side effects peaked within the first 24 hours following vaccination and usually lasted 1-2 days.

The study published by researchers from King's College London of data is the first large scale study to compare the two vaccines and investigate the prevalence of mild side effects of the UK's vaccination programme.

The analysis by the researchers from the ZOE COVID Symptom Study app reassuringly 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% reduction) and AstraZeneca (39% reduction) vaccines compared to a control group. The drop in infection at least 21 days after the first dose for Pfizer is 69% and for AstraZeneca 60%.

This large-scale analysis examined the differences of reported side effects from the two vaccines currently distributed in the UK. Systemic effects - meaning side effects excluding where the injection took place - included headache, fatigue, chills and shiver, diarrhoea, fever, arthralgia, myalgia, and nausea; whilst 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.

Summary of findings:

-25.4 per cent of vaccinated people indicated suffering from one or more systemic (excluding the area where the injection took place) side effects, whereas 66.2 per cent reported one or more local (at the injection site) side effects.

-13.5 per cent of participants reported side effects after their first Pfizer dose, 22.0 per cent after the second Pfizer dose and 33.7 per cent after the first AstraZeneca dose.

-The most-reported systemic side effect was headache.

-The second most reported systemic side effect was fatigue with 8.4% and 14.4% of participants reporting fatigue after the first and second dose of the Pfizer vaccine and 21.1% reported fatigue after their first dose of the AstraZeneca vaccine.

-The most common local side effect was tenderness: 57.2 per cent and 50.9 per cent 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 among people under 55 years of age and among women.

In Phase III clinical trials of the Pfizer vaccine, the most common side effects were pain at the injection site (71-83 per cent), fatigue (34-47 per cent) and headache (25-42 per cent), however, the real-world analysis found less than 30 per cent of users complained of injection site pain and less than 10 per cent of fatigue and headache after the first dose.

Similarly, in Phase III trials for the AstraZeneca vaccine, systemic side effects were found in 88 per cent of younger participants (18-55 years) after the first dose but this study found a significantly lower rate of 46.2 per cent after the first dose.

Professor Tim Spector OBE, lead scientist on the ZOE COVID Symptom Study app and Professor of Genetic Epidemiology at King's College London 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 50's who are most at risk of the infection. Rates of the 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".

"The results also show up to 7 per cent protection after 3 weeks following a single dose, which is fantastic news for the country, especially as more people have now had their second jabs."

Dr Cristina Menni, first author of the study from King's College London said: "Our results support the aftereffects 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."