Vaccines are the safest and most effective way to protect you and those around you from becoming seriously ill with Covid-19, and the UK medicines regulator continues to advise that the benefits of the vaccine outweigh the risks.

But with more than 11 million people in the UK having had both doses of the jab, a small number of people have experienced side effects. Here’s what you need to know.

How rare are the side effects?

According to the NHS, so far millions of people have been given a Covid-19 vaccine and reports of serious side effects, such as allergic reactions or clotting problems, have been very rare. 

However, some people do experience mild side effects like arm soreness, fatigue, headache or a low-grade fever.

But this isn’t necessarily a bad thing. As Dr Gregory Poland, a physician and vaccinologist at the Mayo Clinic in Minnesota told Smithsonian Magazine: “Vaccine reactions are not evidence of something going wrong, but evidence of something going right”.

Vaccine reactions happen because your immune system is mounting a response to the antigen (a molecule that looks like part of a virus) used in Covid-19 vaccines. The antigen in the vaccine will prompt the immune system to respond much as it would have on its first reaction to the actual pathogen.

What are the mild side effects of the vaccine and how should I treat them?

Most side effects of the COVID-19 vaccine are mild and should not last longer than a week. These include: a sore arm where the needle went in, feeling tired, a headache, feeling achy and feeling or being sick.

The NHS says you can take painkillers, such as paracetamol, if you need to. If your symptoms get worse or you are worried, call 111.

What about allergic reactions?

The NHS recommends telling healthcare staff before you are vaccinated if you’ve ever had a serious allergic reaction.

You should not have the COVID-19 vaccine if you have ever had a serious allergic reaction (including anaphylaxis) to a previous dose of the same vaccine or any of the ingredients in the vaccine.

Serious allergic reactions are rare. If you do have a reaction to the vaccine, it usually happens in minutes. Staff giving the vaccine are trained to deal with allergic reactions and treat them immediately.

The Centers for Disease Control and Prevention has also reported that some people experience a red, itchy, swollen or painful rash after receiving a jab. These rashes can start a few days to more than a week after the first shot and are sometimes quite large. These rashes are also known as “COVID arm.”

If you experience “COVID arm” after getting the first shot, the CDC recommends that you should still get the second shot at the recommended interval if the vaccine you got requires a second shot. Tell your vaccination provider that you experienced a rash or “COVID arm” after the first shot. They may recommend that you get the second shot in the opposite arm.

If the rash is itchy, you can take an antihistamine. If it is painful, you can take a pain medication like acetaminophen or a non-steroidal anti-inflammatory drug (NSAID).

How rare are blood clots?

The MHRA is carrying out a detailed review of reports of an extremely rare blood clotting problem affecting a small number of people who have had the Oxford/AstraZeneca vaccine. The problem can also happen in people who have not been vaccinated and it’s not yet clear why it affects some people.

The NHS says: “The COVID-19 vaccine can help stop you getting seriously ill or dying from COVID-19. For people aged 30 or over and those with other health conditions, the benefits of being vaccinated outweigh any risk of clotting problems. For people under 30 without other health conditions, it’s currently advised that it’s preferable to have another COVID-19 vaccine instead of the Oxford/AstraZeneca vaccine.”

What are the symptoms of the extremely rare blood clots and what should I do?

The NHS says to call 111 immediately if you get any of these symptoms starting from around four days to four weeks after being vaccinated:

  • a severe headache that is not relieved with painkillers or is getting worse
  • a headache that feels worse when you lie down or bend over
  • a headache that’s unusual for you and occurs with blurred vision, feeling or being sick, problems speaking, weakness, drowsiness or seizures (fits)
  • a rash that looks like small bruises or bleeding under the skin