One in four people suffer headaches, fatigue and other mild side effects from Covid vaccines – and rates are twice as high for AstraZeneca’s jab, real-world study shows

  • ZOE Covid Symptom Tracking Study suggests fewer suffer mild side effects 
  • King’s College London scientists found side effects peak in the first 24 hours 
  • Epidemiologists professor Tim Spector said results should ‘reassure many’

Just one in four people suffer mild side effects after taking a coronavirus vaccine, real-world data has shown.

Data from the ZOE Covid Symptom Tracking Study — a surveillance tool that tracks Britain’s outbreak — showed headaches, fatigue and fever were more common with the AstraZeneca vaccine. 

A third of recipients suffered mild side effects after their first dose, compared to 13.5 per cent for Pfizer’s rival jab. However, Pfizer’s top-up dose caused slightly more side effects (22 per cent). 

King’s College London scientists also found the effects peaked in the first 24 hours of being vaccinated and usually last two days before fading on their own. Headaches were the most common side effect. 

The data released by this study did not include numbers for ultra-rare blood clots in the brain, which have been linked to the AstraZeneca jab. 

Lead researcher Professor Tim Spector said the results of the study should ‘reassure many people that in the real world, after effects of the vaccine are usually mild and short-lived’. 

Just one in four people suffer mild side effects from AstraZeneca and Pfizer vaccines, real-world data from the ZOE Covid Symptom Study and King’s College London shows – 66% less than clinical trials suggested

Pictured: Matt Willis is vaccinated by his wife Emma while volunteering for St John Ambulance today

Experimental trials for the Pfizer and AstraZeneca vaccines last year suggested mild side effects were far more common for both company’s jabs.

Pfizer’s clinical Phase 3 trial showed 77.4 per cent of people experienced at least one systemic side effect after their first jab.

And AstraZeneca’s trials suggested 75.8 per cent of people suffered mild systemic side effects after a first vaccination.

The MHRA says one in 10 people suffer headaches, chills, feverish symptoms and nausea after taking the vaccine.  

The positive data comes as England opened up the vaccine roll-out to people aged over-42, with 1.3million more people invited to take their first vaccine.

Health Secretary Matt Hancock said he was ‘excited’ to have his first jab now that people in his own age range would be receiving invitations for a vaccine.

More than 33.9million people have now had a first dose of the vaccine in the UK, with a quarter now fully vaccinated. 


The Medicines and Healthcare products Regulatory Agency (MHRA) has listed the below as side-effects of the AstraZeneca vaccine.

Very Common (may affect more than one in 10 people)

  • Tenderness, pain, warmth, itching or bruising where injection is given;
  • Generally feeling unwell;
  • Feeling tired (fatigue);
  • Chills or feeling feverish;
  • Headache;
  • Feeling sick (nausea);
  • Joint pain or muscle ache.

Common (may affect up to one in 10 people)

  • Swelling, redness or lump at the injection site;
  • Fever;
  • Being sick (vomiting) or diarrhoea;
  • Flu-like symptoms, such as high temperature, sore throat, runny nose, cough and chills.

Uncommon (may affect up to one in 100 people)

  • Rash, excessive sweating or itchy skin.
  • Feeling dizzy;
  • Decreased appetite;
  • Abdominal pain;
  • Enlarged lymph nodes;

Source: MHRA

The ZOE study, published in Lancet Infectious Diseases today, showed that 25.4 per cent of vaccinated people reported mild systemic side effects — side effects that are not located in the area a person was injected.

Systemic effects included headache, fatigue, chills and shiver, diarrhoea, fever, arthralgia (joint pain), myalgia (muscle pain), and nausea.

Local side-effects — where the injection took place — included arm pain, swelling, tenderness, redness, itch, warmth and swollen armpit glands.

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.  

Headaches were the most common side effect for both vaccines, with 22.8 per cent of AstraZeneca recipients reporting it. Some 7.8 per cent of people reported suffering from headaches after the first Pfizer dose and 13.2 per cent after the second Pfizer dose.

People who had been infected with Covid before were three times as likely to have full-body side effects from the first dose of the Pfizer vaccine as those who had not suffered with a known infection before. 

They were also twice as likely to experience the effects as those having a first dose of AstraZeneca’s jab. 

The study also showed that side effects were most common in people aged under-55 and in women.  

Professor Spector 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-50s 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 per cent protection after three 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 added the study should help ‘allay safety concerns’ about both companies’ vaccines.

She 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.’ 

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