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18th December, 20208 min read

COVID-19 vaccines: all you need to know

Medical reviewer:Healthily's medical team
Author:Ceri Moorhouse
Last reviewed: 14/12/2020
Medically reviewed

All of Healthily's articles undergo medical safety checks to verify that the information is medically safe. View more details in our safety page, or read our editorial policy.

Since the start of the COVID-19 (coronavirus) pandemic, groups of scientists around the world have been working to come up with a vaccine – and now several countries are either already vaccinating people or are about to start.

The UK was the first country to approve and use a vaccine that had been tested in a large trial – the Pfizer/BioNTech vaccine.

The Oxford/AstraZeneca vaccine is also being given to people in the UK and the Moderna vaccine has been approved for use.

In the USA, the Pfizer/BioNTech vaccine, the Moderna vaccine and the Johnson & Johnson (Janssen) vaccine are approved for emergency use.

And in India, the Oxford/AstraZeneca vaccine (known locally as Covishield) and Covaxin have been approved for emergency use.

Other COVID-19 vaccines may be approved soon, and there are many more vaccines in development.

Here are the key things you need to know about COVID-19 vaccines, including how they work and when you might get one.

How do COVID-19 vaccines work?

A vaccine works by training your body’s defences (immune system) to spot and fight off the virus or bacteria it’s designed for. If you’re then exposed to those germs, the vaccine will stop you from getting ill.

There are several types of vaccine being made for COVID-19, including:

  • inactivated virus vaccines. These use a form of the virus that has been made safe. This means they won’t make you ill, but your immune system will still respond
  • viral vector vaccines. These use a virus that has been made (genetically engineered). Again, they don’t cause disease, but they make your immune system respond. The Oxford/AstraZeneca vaccine is a viral vector vaccine
  • protein-based vaccines. These use pieces of protein that imitate the virus to make your immune system respond
  • RNA and DNA vaccines. These use genetic information to create a protein that makes your immune system respond. The Pfizer/BioNTech and Moderna vaccines are RNA vaccines

How quickly does the COVID-19 vaccine start working?

After having a COVID-19 vaccination, it usually takes the body a few weeks to make the white blood cells that fight the virus. This means it’s possible to get COVID-19 just before or after having the vaccine and then become unwell because the vaccine didn’t have enough time to work.

Do the pneumonia vaccines work against COVID-19?

Unfortunately, vaccines for pneumonia don’t work for COVID-19, which is why scientists have had to create new vaccines. They can help protect you from pneumonia, which is another respiratory illness (see here for more information).

When will I get a COVID-19 vaccine?

When you’ll be offered a COVID-19 vaccine depends on several things, including which country you live in, your government’s plans, and how at risk you are from the virus.

The World Health Organization (WHO) says certain groups of people should get the vaccine first, because they’re at high risk. These include frontline health and care workers who are likely to get infected, older adults, and people at a high risk of death from the virus because of other health conditions (such as diabetes or heart disease).

The WHO says other groups of people should get a vaccine after these priority groups have been protected, when more doses of vaccine are available. So if you don’t belong to a high-risk group, you may have to wait a while.

Do I need a COVID-19 vaccine if I’ve already had the virus?

You’ll be offered the vaccine whether or not you’ve had COVID-19 and recovered. If you currently have COVID-19, you should check the guidance in your country on how long to wait before having the vaccine.

How is a COVID-19 vaccine given?

Most of the COVID-19 vaccines being developed are given by injection and you’ll need 2 doses, given at different times.

The latest evidence suggests that the first dose of the vaccine provides considerable protection in the short term. Because of this, in the UK, when you have the 2nd dose changed. Previously, the 2nd dose was given 21 days after the 1st dose. Now, it is given 12 weeks after the first dose.

In the US, the Pfizer/BioNTech vaccine is given in 2 doses with 21 days between them. The Moderna vaccine is also given in 2 doses, but needs to be given 28 days apart.

The Johnson & Johnson vaccine is given in a single dose.

What are the side effects of the COVID-19 vaccine?

Like all medicines, vaccines can cause side effects. However, most side effects of the COVID-19 vaccine are mild and shouldn’t last longer than a week. They include:

  • pain, redness and swelling in the arm you got the injection
  • feeling tired
  • a headache
  • feeling achy
  • muscle pain
  • joint pain
  • nausea
  • feeling unwell
  • fever
  • chills
  • swollen lymph nodes (lymphadenopathy)

In a very few cases, people have had an allergic reaction to the vaccine. This is most likely to happen within a few minutes to an hour of being vaccinated. If you think you’re having an allergic reaction, call for urgent medical help.

The Oxford/AstraZeneca vaccine and blood clots

Some countries have paused using the Oxford/AstraZeneca coronavirus vaccine after a number of people who were given it had blood clots afterwards. 

While many of these countries have since started using it again, advice on how it should be used has now changed.

The European Medicines Agency (EMA) has said that unusual blood clots combined with low blood platelets should be listed as a very rare side effect of the Oxford/AstraZeneca vaccine.

If you have any of the following symptoms more than 4 days and within 28 days of the COVID-19 vaccination, you should get medical help urgently:

  • new onset of severe headache, which is getting worse and does not respond to simple painkillers
  • an unusual headache which seems worse when lying down or bending over, or may be accompanied by blurred vision, nausea and vomiting, difficulty with speech, weakness, drowsiness or seizures
  • new unexplained pinprick bruising or bleeding
  • shortness of breath, chest pain, leg swelling or persistent abdominal pain

Is the COVID-19 vaccine safe?

In the UK, the approved COVID-19 vaccines have gone through all the clinical trials and safety checks that all other licensed medicines have to go through.

In the USA, the US Food and Drug Administration (FDA) has issued something called an ‘Emergency Use Authorization’ (EUA) for the vaccines being used there. An EUA may be given if a vaccine is in the final stage of clinical trials, but trials have not yet finished. This happens when the FDA decides that the benefits outweigh any risks.

Advice if you’re pregnant or breastfeeding

There isn’t evidence that the vaccine is unsafe for people who are pregnant or breastfeeding, but more evidence is needed before it’s routinely offered to them.

People who are pregnant may be able to have the vaccine if they’re at high risk of exposure to or severe illness from COVID-19. People who are breastfeeding may also be able to have the vaccine.

If you are pregnant, you should only get the Oxford/AstraZeneca vaccine if your doctor advises you that the benefits outweigh the risks.

If you’re pregnant or breastfeeding, you may want to speak with a healthcare professional before having the vaccine.

Advice if you have an underlying medical condition

People with certain underlying medical conditions are at high risk of severe illness from COVID-19. They may have the vaccine, as long as they haven’t had a serious allergic reaction to a COVID-19 vaccine or any of the vaccine’s ingredients.

This includes people who are immunosuppressed. However, it is not yet clear how effective the vaccine is for these people. If you’re immunosuppressed, it is very important to keep taking measures to protect yourself from catching COVID-19, even once you have had the vaccine.

The vaccine is safe for people with lung conditions.

If you are at higher risk of blood clots because of a medical condition, you should only get the Oxford/AstraZeneca vaccine if your doctor advises you that the benefits outweigh the risks.

If you have an underlying medical condition and are in any way unsure if you should have the vaccine, you should speak with a healthcare professional before having it.

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