Here’s what we know so far about the after-effects of the Oxford AstraZeneca COVID vaccine

April 14, 2021

Millions of people in the UK have received the Oxford AstraZeneca COVID-19 jab. Here’s what we know so far about the vaccine and its after-effects.

How does the Oxford AstraZeneca COVID-19 vaccine make you feel?

COVID-19 vaccines work by using a harmless version of the SARS-CoV-2 coronavirus to train the immune system, so when we encounter the virus for real we’re able to fight it off. 

This ‘training’ response can feel a bit like the effects we get when we’re fighting off a real infection. These whole body (systemic) effects include headaches, fever, chills or shivers, tiredness (fatigue), muscle or joint pains, diarrhoea and feeling sick (nausea). 

It’s also common to experience local effects like pain, swelling, redness or itchiness at the site of the injection, or swelling of the glands (lymph nodes) in the armpit.

While they may make you feel grotty, all these effects are a sign that your immune system is kicking into action to protect you from COVID-19. 

At the same time, don’t worry if you don’t experience any of these effects after your vaccine. Your immune system will still be learning to respond to the virus.

How many people have after-effects from the Oxford AstraZeneca COVID-19 vaccine?

We’ve been asking everyone who gets vaccinated to log their jab and tell us how they feel, so we can understand more about the impact of the new COVID-19 vaccines and their effects. 

So far, more than a million people have logged their vaccinations with ZOE, and our data team has analysed reports from 345,280 who received their first dose of the Oxford AstraZeneca vaccine.

We found:

  • Around one in three people (34%) who received one dose of the Oxford AstraZeneca vaccine experienced at least one systemic effect, compared with roughly one in eight getting the Pfizer jab
  • Most symptoms happen in the first 24 hours after vaccination, with headache, fatigue and chills and shivers being the most common
  • Almost half (46%) of the participants under 55 years old were likely to experience after-effects, compared to 31% of over 55s
  • More than half of people (59%) who received the Oxford AstraZeneca jab had at least one after-effect in their arm, most commonly tenderness and pain in the day or two after the jab. 

Line graph showing rate of symptoms experienced after 1st AstraZeneca vaccine dose


Do you feel worse after vaccination if you’ve already had COVID-19?

Our research shows that people who had previously experienced COVID-19 were more likely to experience the systemic (whole body) effects after vaccination. 

Around half of people (53%) who’d had COVID-19 in the past reported at least one systemic effect within seven days of getting the Oxford AstraZeneca vaccine, compared with around a third (33%) who haven't had COVID-19 in the past. There was no difference between people who had caught COVID-19 recently or had it more than 6 months ago.


Bar graph comparing rate of systemic effects after vaccination


Is the AstraZeneca vaccine working?

While the full course of the AstraZeneca vaccine is two shots up to 12 weeks apart, the good news is that it seems to provide some degree of protection after just the first dose.

Our data shows a 39% reduction in infection rates between 12 to 21 days after the first dose of the AstraZeneca vaccine, improving to a 60% reduction after 21 days. 

Can you still catch COVID-19 after being vaccinated?

No vaccine provides 100% protection, and it is possible to  catch COVID-19 after being vaccinated, especially in the first few weeks.

It’s important to make sure that you follow the guidelines on social distancing, wearing face coverings, ventilation and hygiene to protect yourself and others around you, even once you’ve been vaccinated.

Remember that the after-effects of vaccination can look a lot like COVID-19 symptoms. If you’re logging your symptoms in the app after getting your jab and are offered a COVID test, please take it.

You should get a test and self-isolate if you are still feeling unwell several days after your jab, especially if you lose your sense of smell (anosmia) or develop a persistent cough. 

Want to be part of the largest independent community-led COVID vaccine study in the world? Log your jab with ZOE

We need to gather as much data as we can about the impact and any after-effects of COVID-19 vaccines to support the rollout and help end the pandemic. 

If you’re not already using it, download the ZOE COVID Symptom Study app and use it to record your COVID-19 vaccine, followed by daily health reports to help us monitor the after-effects and impact of vaccination. 

You can also register a profile and log reports on behalf of relatives or people you are caring for who may not be able to use the app themselves. 

By logging your vaccination you’ll be part of the largest independent community-led COVID vaccine study in the world, providing vital information to ensure public safety and help end the pandemic.

Together we’ll get through this. Stay safe and keep logging.

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