Millions of people have had a coronavirus (COVID-19) vaccine and the safety of the vaccines continues to be monitored. Reports of serious side effects are very rare. Find out about COVID-19 vaccine safety and side effects for children aged 12 to 15 on COVID-19 vaccine for children.
Like all medicines, the COVID-19 vaccines can cause side effects, but not everyone gets them.
Most side effects are mild and should not last longer than a week, such as:
- a sore arm from the injection
- feeling tired
- a headache
- feeling achy
- feeling or being sick
You may also get a high temperature or feel hot or shivery 1 or 2 days after your vaccination. You can take painkillers such as paracetamol if you need to. If your symptoms get worse or you're worried, call 111.
If you have a high temperature that lasts longer than 2 days, a new, continuous cough or a loss or change to your sense of smell or taste, you may have COVID-19. Stay at home and get a test.
You cannot catch COVID-19 from the vaccine, but you may have caught it just before or after your vaccination.
Find out more about what to expect after your COVID-19 vaccination on GOV.UK
Most people with allergies (including food or penicillin allergies) can be vaccinated against COVID-19.
Tell healthcare staff before you're vaccinated if you've ever had a serious allergic reaction (including anaphylaxis). They may ask what you're allergic to, to make sure you can have the vaccine.
Serious allergic reactions to the COVID-19 vaccines are very rare.
If you do have a reaction, it usually happens in minutes. Staff giving the vaccine are trained to deal with allergic reactions and treat them immediately.
If you have a serious allergic reaction to the 1st dose of a vaccine, you should not have the same vaccine for your 2nd dose.
Blood clotting
The MHRA is carrying out a detailed review of reports of an extremely rare blood clotting problem affecting a small number of people who had the Oxford/AstraZeneca vaccine.
It's not yet clear why it affects some people.
The COVID-19 vaccine can help stop you getting seriously ill or dying from COVID-19. For people aged 40 or over and those with other health conditions, the benefits of being vaccinated with the Oxford/AstraZeneca vaccine outweigh any risk of clotting problems.
For people under 40 without other health conditions, it's preferable for you to have the Pfizer/BioNTech or Moderna vaccine instead of the Oxford/AstraZeneca vaccine.
Find out more about COVID-19 vaccination and blood clotting on GOV.UK
You get any of these symptoms starting from around 4 days to 4 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 along 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
- shortness of breath, chest pain, leg swelling or persistent abdominal (tummy) pain
Heart inflammation (myocarditis)
There have been rare cases of inflammation of the heart (myocarditis) reported after COVID-19 vaccination. Most people who had this recovered following rest and simple treatments.
Get urgent medical advice if you have any of these symptoms within a few days of being vaccinated:
- chest pain
- shortness of breath
- a fast-beating, fluttering or pounding heart (palpitations)
COVID-19 vaccines have to go through several stages of clinical trials before they can be approved for use.
Clinical trials are where a vaccine or medicine is tested on volunteers to make sure it works and is safe.
The approved COVID-19 vaccines have been tested on thousands of people in the UK and around the world, including:
- people from different ethnic backgrounds
- people aged between 18 and 84
- children and young people aged between 12 and 17
- people with different health conditions
All vaccines used in the UK must be approved by the independent Medicines and Healthcare products Regulatory Agency (MHRA).
The MHRA makes sure the vaccines meet strict international standards for safety, quality and effectiveness. Once a vaccine is approved, it's closely monitored to continue to make sure it is safe and effective.
This video explains how the COVID-19 vaccines were developed quickly but safely.
Like with any vaccination, there is potential for side effects after you get your shot. The good news is that the COVID-19 vaccines have similar side effects that are typically mild and don’t last long — about one to three days.
The most common side effects include a sore arm, fatigue (feeling tired), headache, aches, and fever. Severe side effects are very rare and treatable.
It is difficult to predict. Side effects are more common, and may be more pronounced, after the second dose of Pfizer-BioNTech COVID-19 vaccine (Comirnaty®) or Moderna COVID-19 vaccine (Spikevax™).
Back to topIf you get side effects, they are a good sign — they indicate that the vaccine is working by triggering the immune system.
When you get vaccinated, your immune system recognizes something as being foreign. The immune system automatically launches a small-scale attack against it. This process teaches your immune cells to recognize and respond to an “invader.” That’s why you might experience some side effects. Think of it this way: The body’s response to the vaccine is like a training mission for the real fight.
Once you’re fully vaccinated, if you were infected by the virus causing COVID-19, your immune system would be ready to launch an even larger and more powerful attack to protect you.
If you don’t experience any side effects, that doesn’t mean that the vaccine didn’t work. In the vaccine clinical trials, more than half of people didn’t experience any side effects but we still know that the vaccine was effective in those people.
Back to topIf you have pain or discomfort after receiving your vaccination, talk to your doctor about taking an over-the-counter medicine, such as ibuprofen (Advil) or acetaminophen (Tylenol).
To reduce pain and discomfort on your arm:
In most cases, discomfort from fever or pain is normal. Contact your doctor or healthcare provider:
Back to topYou should wait until after being vaccinated to see how you feel. If you do experience side effects, it is OK to take an over-the-counter drug (like Advil or Tylenol) to lower a fever, reduce chills, or relieve a headache or body aches. It’s important that you do not take these drugs before getting your vaccine as there are theoretical concerns that some pain relieving drugs may interfere with the immune response to the vaccine. It is also unclear if taking medication ahead of time actually works to reduce post-vaccine symptoms.
Back to topA few extremely rare instances of severe side effects have emerged and been investigated, but scientists have concluded the risk of getting severely ill from COVID-19 is far greater than the risk of these side effects. Here is proof of this careful and ongoing scrutiny:
Back to topSome patients who receive either the Pfizer-BioNTech or Moderna vaccines may experience some swelling or tenderness in their lymph nodes. It is also possible that this swelling will show up on imaging tests and could be mistaken for progression of certain cancers — primarily breast, head and neck, melanoma, and lymphoma.
This vaccine side effect is more common after the second dose, usually occurs within two to four days after the vaccination, and can last for an average of 10 days.
On imaging tests, the lymph node enlargement may be detected for a longer period. For these reasons, we recommend:
It’s important to know that all kinds of vaccines can cause temporary swelling of the lymph nodes, which may be a sign that the body is making antibodies in response as intended.
Back to topShould I get an antibody test after the vaccine to make sure it’s working?
Antibody testing is not currently recommended check someone’s immunity to COVID-19 following either the Pfizer-BioNTech or Moderna vaccines. The COVID-19 antibody test used at MSK detects the immune response after being infected by COVID-19. It does not measure immunity that results from the vaccine. That’s why it should not be routinely ordered to assess vaccine response.
Back to topThe COVID-19 vaccines are among the most effective vaccines in history. They are as effective — if not more — than vaccines for polio, chicken pox, measles and the flu.
The chances of getting sick after vaccination are minimal. Studies show even if you develop COVID-19 after being vaccinated, you are unlikely to get severely ill. Flu vaccines are less effective than the COVID vaccines, but they can protect you from more severe flu illness and hospitalization. The COVID-19 vaccines are even more powerful.
Learn more about the COVID-19 vaccines »
December 17, 2021