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COVID vaccine – your questions answered

Dr Roger Henderson
Reviewed by Dr Roger HendersonReviewed on 13.10.2023 | 3 minutes read

With the COVID-19 vaccine having been put into place across the world now, the doctors here at Healthwords have listened to many of the public’s pressing questions in their frontline work so let’s address your concerns and give you the information you need to decide on taking up the offer of the vaccine if you still haven’t had it, either for yourself or a loved one.

Is the vaccine safe? Can I catch COVID from it?

The vaccines approved for use in the UK have gone through rigorous and careful clinical testing in order to be licensed and deemed safe for use. No steps were skipped in this process but the steps were run concurrently, in order to help get the vaccine fully tested and proven to be safe as soon as possible.

A very small number of people may experience a serious allergic reaction to the vaccine (this is similar with many vaccines and medications). This is why vaccine centres have doctors on hand to treat allergic reactions.

Although rare, experience from other vaccines has taught us that any serious allergic reaction will happen within a few minutes of your vaccine being given. For some, you may be asked to wait for 15 minutes after being vaccinated, to ensure you’re well.

The vaccine can't give you the COVID-19 infection or disease as – unlike some other vaccines – this vaccine does not contain a live virus. However, the nature of a vaccine is to provoke your immune system to make a response, so it's primed to respond faster and more efficiently to kill the actual virus if it meets it. So this means you may get some of the symptoms.

Another possibility is that you have caught COVID-19 in the days before the vaccine or just after it, without realising it. Symptoms tend to only start after five days or more, so your symptoms may appear after you have been vaccinated, but the vaccine is not to blame.

Can I still catch COVID if I’ve had the vaccine?

Yes, you can still catch COVID-19 once vaccinated. It takes one to two weeks after the first vaccination for your immunity to build up against COVID-19, with the best immunity after the second dose. After this time you are less likely to be infected with COVID-19, but no vaccine offers 100% protection.

It also relies on either infection rates being low in the community or lots of people getting the vaccine (the so-called herd immunity). On top of this, the virus is replicating billions of times across the world, and mutations will arise in this process of replication – a working vaccine today may not be effective against a new strain of COVID-19 tomorrow.

You can minimise your chance of catching it or passing it on by keeping your distance, wearing a face mask in enclosed spaces and maintaining good hand hygiene. Fortunately, if you do catch it while vaccinated, it's likely to be a much milder illness.

What should I expect in the days after the vaccine?

The most common side effects after having the vaccine are a sore arm, tiredness, headache and mild flu-like symptoms like fever, chills and muscle aches.

These side effects are normal and are due to your body’s immune system working to build up protection to COVID-19. They tend to occur after one to two days and start to go away after the third day.

If you have a high temperature, severe symptoms, symptoms that are not improving after four or five days or you’re concerned, you should call NHS 111 for help and advice. It may be that it's not side effects from the vaccine and but rather COVID-19 infection (caught before being vaccinated) or another illness.

Do I still need to isolate if I've been vaccinated?

The rules have changed slightly with this, and it's now the same, whether you've had no vaccination, or you've received one jab, both or the booster.

It's now recommended you self-isolate for at least 5 days and avoid vulnerable people for 10 days in one of three circumstances: if you have the three classic symptoms (new persistent cough, high temperature or change to their sense of taste and smell), if you've tested positive for COVID (on PCR or lateral flow test), or if someone you live with has had symptoms or tested positive.

Self-isolation is now recommended rather than enforced by law in the UK.

*Information correct on 9 February 2023

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Dr Roger Henderson
Reviewed by Dr Roger Henderson
Reviewed on 13.10.2023
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