London, Apr 28 (IANS): One in four people experience mild, short lived systemic side effects like headache, fatigue and tenderness after receiving either the Pfizer or AstraZeneca vaccine, according to a new study published in the journal Lancet Infectious Diseases.

Most side effects peaked within the first 24 hours following vaccination and usually lasted 1-2 days, and majorly among women under 55 years of age, said researchers from the King's College London.

"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," Tim Spector, Professor of Genetic Epidemiology at the varsity.

"The results also show up to 70 per cent protection after 3 weeks following a single dose," Spector said.

The team analysed data 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 findings showed 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 injection site) side effects.

About 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 -- 7.8 per cent of people after the first Pfizer dose and 13.2 per cent after the second Pfizer dose, while 22.8 per cent of people reported headache after the first dose of the AstraZeneca vaccine.

Nearly 8.4 per cent and 14.4 per cent people reported fatigue after the first and second dose of Pfizer vaccine, whileA 21.1 per cent reported fatigue after their first dose of AstraZeneca vaccine.

A whopping 57.2 per cent and 50.9 per cent reported tenderness after the first and second dose of Pfizer vaccine, and 49.3 per cent after the first dose of AstraZeneca vaccine, the researchers said.

The study also reports a significant decrease of infection rates from 12 to 21 days after the first dose of the Pfizer (58 per cent reduction) and AstraZeneca (39 per cent reduction) vaccines compared to a control group.

The drop in infection at least 21 days after the first dose for Pfizer is 69 per cent and for AstraZeneca 60 per cent, the findings showed.

Moreover, Covid survivors 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 and almost twice more likely after the first dose of the AstraZeneca vaccine.