COVID: Only One-Quarter Experience Systemic Vaccine Side-Effects

The systemic and local side-effects of Pfizer-BioNTech and Oxford-AstraZeneca COVID vaccines.

The systemic and local side-effects of Pfizer-BioNTech and Oxford-AstraZeneca COVID vaccines.

One-quarter of people who receive either the AstraZeneca or Pfizer COVID vaccines experience systemic effects.

Headache, fatigue, tenderness and pain around the injection site are the most common systemic and local effects but they were mild and do not last long, a UK real-world study found.

Systemic effects are adverse reactions affecting the whole body except for the site of contact: these include fatigue, headache, joint pain, myalgia, fever, chills and shiver, nausea, and diarrhoea.

Local effects are those adverse reactions that occur at the site of injection which include tenderness, swelling, pain in the arm, itch, warmth, redness, and swollen lymph nodes in the armpit.

Allergic skin reactions were also reported by some people across both types of vaccine, including red welts on face and the lips, rashes, and skin burning.

Most side-effects were minor in severity occurring during the first 24 hours after vaccination and often lasting up to 2 days.

The data was gathered from 627,383 users of the ZOE COVID Symptom Study app in the UK.

In addition, the study found that infection rates dropped by 58 percent 12 days after the first dose of the Pfizer vaccine but for AstraZeneca it was a 39 percent.

The reduction in infection rates at 21–44 days after the first injection for Pfizer was 69 percent and for AstraZeneca 60 percent.

Here is a brief summary of the outcomes:

  • 25.4 percent of participants experienced one or more systemic adverse effects and 66.2 percent had one or more local adverse effect.
  • 22.8 percent of people suffered from headaches after the first dose of the AstraZeneca vaccine while 7.8 percent of people after the first Pfizer jab and 13.2 percent after the second Pfizer dose reported headaches.
  • 21.1 percent of people experienced fatigue while 8.4 percent of people had fatigue after the first Pfizer jab and 14.4 percent after the second dose of Pfizer.
  • Tenderness was the most common local effect: 49.3 percent after the first dose of AstraZeneca, 57.2 percent after the first Pfizer jab and 50.2 percent after the second dose of Pfizer.

It appears that side-effects were more common among women and people who were 55-years-old or younger.

People with a previous COVID infection were 3 times more likely to suffer from vaccine related side-effects.

Professor Tim Spector, the study’s senior author, 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 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 70% 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.”

About the author

Mina Dean is a Nutritionist and Food Scientist. She holds a BSc in Human Nutrition and an MSc in Food Science.


The study was published in the Lancet Infectious Diseases (Menni et al., 2021).


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This site is all about scientific research into how the mind works.

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