COVID vaccine – your questions answered

The vaccines approved for use in the US 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 centers 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 realizing 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.

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 minimize 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.

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 your doctor for help and advice. It may be that it's not side effects from the vaccine but rather COVID-19 infection (caught before being vaccinated) or another illness.

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

It's now recommended you self-isolate for at least 5 days and avoid vulnerable people if you have symptoms or test positive for COVID (on PCR or lateral flow test). Symptoms vary but can include fever, cough, shortness of breath, fatigue, headache, loss of taste or smell, nausea, and diarrhea. Isolate for 10 days if you have moderate to severe symptoms.