How to tell the difference between COVID-19 symptoms and vaccine after effects

April 28, 2021

The after effects of your COVID jab can be very similar to COVID-19 symptoms. Here’s how to tell the difference and know when to get a test.  

  • How will I feel after my vaccine?
  • Will I experience vaccine after effects?
  • How do I know whether I have vaccine after effects or COVID-19?
  • Help us understand the effects and impact of COVID-19 vaccines by logging your jab

As of the beginning of April, tens of millions of people in the UK have received at least one dose of a COVID-19 vaccine. 

Thanks to more than one million ZOE COVID Symptom Study contributors who have logged their jabs in the app, we’ve been able to look in detail at the effects and impact of COVID-19 vaccines.

Confusingly, the after effects of vaccination can feel a lot like some of the symptoms of COVID-19, making it hard to know whether you’re experiencing a response to the vaccine or have caught the virus  and should self-isolate and get tested.

It’s important to remember that you can still catch COVID-19 after being vaccinated, particularly in the first couple of weeks after your jab, as it takes time for your immunity to build up and no vaccine provides 100% protection. 

So it’s important to be alert to any signs that you may be infected, to help protect both yourself and the people around you.

How will I feel after my COVID vaccine?

It’s hard to predict how you will feel after getting your COVID jab, as the after effects vary from person to person. Your immune system will still be learning to respond to the virus so  you shouldn't worry if you don’t experience anything after your jab. 

Vaccine after effects fall into two groups:

1. Local effects

Most commonly tenderness and local pain at the site of the jab but also includes local redness, itching or warmth and swelling of the glands (lymph nodes) in the armpit. These peak the day after your vaccine and tend to last just over a day.

2. Systemic (whole body) effects

Most commonly fatigue and headache but also includes fever, chills or shivers, muscle or joint pains, diarrhoea and feeling sick (nausea). These peak around 24 hours after your jab and stick around for a day or two.

It’s these systemic after effects that can easily be confused with some of the symptoms of COVID-19

Will I experience vaccine after effects?

It’s normal not to feel quite right in the first few days after your vaccine. A third of people (34%) who have the Oxford AstraZeneca vaccine experience at least one systemic effect, while roughly one in eight experience systemic effects after having the first dose of the Pfizer jab.

You’re more likely to experience side effects after their first vaccine dose if you’ve previously had COVID-19. You’re also slightly more likely to report systemic and local effects after the second dose of the Pfizer jab compared with the first.

You can find out more about the specific after effects of the Pfizer and Oxford AstraZeneca vaccines on our blog, and watch our expert webinar to discover how they affect different people.

How do I know whether I have vaccine after effects or COVID-19?

Systemic effects following a vaccine can feel a lot like COVID-19 symptoms. However, there are some key differences. 

  • Vaccine after effects usually only last for a short period of time, and disappear within a day or two. If you’re still feeling unwell several days after your jab, you should self isolate and get a test to check whether you have COVID-19. 

If you’re using the ZOE COVID Symptom Study app to log daily health reports after being vaccinated, you won't be offered a test if symptoms that could be related to your jab only occur in the first three days. 

If your symptoms persist for four or more days, or if you’re reporting symptoms that are unrelated to your vaccine but could be COVID-19, you will be offered a PCR test through the app. We recommend taking a test if you’re offered it. 

As lockdown eases, it’s still important to get tested if you’re worried you have COVID-19 to help protect the people around you and the wider community.

Help us understand the effects and impact of COVID-19 vaccines by logging your jab

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. 

Your contributions are helping to reveal how well vaccines are working and keeping us ahead of  new viral strains that can evade the protection provided by current vaccines or previous coronavirus infections.

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

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