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18th December, 20208 min read

COVID-19 vaccines: all you need to know

COVID-19 vaccines: all you need to know
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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. China and Russia started giving some vaccines earlier than the UK, before tests had been completed.

The Oxford/AstraZeneca vaccine is also being given to people in the UK and the Moderna vaccine has been approved for use, though supplies of this third vaccine may not arrive until the spring.

In the USA, the Pfizer/BioNTech vaccine and the Moderna vaccine are approved for emergency use. And in India, the Oxford/AstraZeneca vaccine and Covaxin have been approved for emergency use. Covaxin has been approved before tests have been completed.

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, when you might get one, and how effective they are.

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

Doctor preparing the coronavirus COVID-19 vaccine

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 wait until you’ve recovered and are allowed to stop isolating. The guidance in the UK says you should wait at least 4 weeks after the start of symptoms, or after your positive test if you didn’t have any symptoms.

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 has 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.

Syringe with medicine in the hands of a doctor in blue gloves

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:

  • a sore arm at the injection site
  • feeling tired
  • a headache
  • feeling achy

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.

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’re pregnant or breastfeeding, you should 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 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 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.

How effective is a COVID-19 vaccine?

How well the COVID-19 vaccine works varies, depending on which vaccine you have. The effectiveness of the 3 main vaccines currently being used/developed is as follows:

  • the Pfizer/BioNTech vaccine is said to be 95% effective from 28 days after the first dose
  • early tests of the Moderna vaccine suggest it is 94.5% effective
  • Oxford/AstraZeneca says its vaccine has an overall effectiveness of 70%

It’s worth bearing in mind that when Pfizer/BioNTech say its coronavirus vaccine is 95% effective, it doesn’t mean the vaccine will work in 95 out of 100 people.

A vaccine’s effectiveness (known as efficacy) is worked out by comparing the risk of disease for people who have been vaccinated with people who haven’t. So, 95% effectiveness means that a group of vaccinated people would have 95% fewer cases of the virus than they would if they hadn’t been vaccinated.

In the tests for the Pfizer/BioNTech vaccine, there were 170 confirmed cases of COVID-19 among the people taking part. In this group of 170 people, 162 hadn’t been given the vaccine, and 8 had.

Something else to remember is that the vaccine tests have been carried out in scientific conditions. At the moment, no one knows for sure how well the vaccines will work in the real world. For that, we will have to wait and see.

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Important: Our website provides useful information but is not a substitute for medical advice. You should always seek the advice of your doctor when making decisions about your health.

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