Patient information from BMJ

Coronavirus (COVID-19): vaccines

Last published:Feb 27, 2023

Several vaccines are now available to protect people against COVID-19. Vaccination programs have now happened in many countries including the US.

This information explains what the vaccines do, how they are given, who can have them, and how safe they are.

We are learning more about these vaccines all the time. So some of the advice about them might change as we find out more.

What is a COVID-19 vaccine?

The COVID-19 virus spread around the world in 2020 and is still infecting people. Millions of people have become sick and many have died.

Scientists in several countries have now developed vaccines to help protect against the virus. For example, in the US, there are currently several vaccines, including:

• the Pfizer/BioNTech vaccine

• the Novavax vaccine

• the Moderna vaccine, and

• the Janssen vaccine.

These vaccines offer protection against the virus that causes COVID-19. But this doesn’t mean that they will always work for everyone - there are no perfect vaccines. But the COVID-19 vaccines will work for most people.

This means that people who become infected after having the vaccine are much less likely to become ill than if they don’t have the vaccine.

The vaccines do the same job, but they are slightly different in the way they work and in the protection they provide.

The type of vaccine that your healthcare professional offers you might depend on what is available locally and what is most suitable for you.

How is the vaccine given?

You get the vaccine as a shot into the muscle of the upper arm.

For the Pfizer and Moderna vaccines, you will need two doses of the vaccine, several weeks apart.

Your healthcare professional will let you know when the second one is due.

For the Janssen vaccine you need just one dose.

If you have the Pfizer vaccine, you will need to wait for 15 to 30 minutes before you can go home. This is so the doctor can keep an eye on you, in case you have any side effects that suggest that you might be allergic to the ingredients of the vaccine.

If you have have an allergic reaction after the vaccine, you might need treatment. This will usually be an injection of epinephrine.

You might be familiar with this type of treatment if you know someone who has allergies and who has to carry an injector, sometimes called an 'EpiPen', which they can use to treat themselves if they have an allergic reaction.

Who can have the vaccine?

Most adults can have the vaccine, although the rules vary a little between the vaccines. For example, in the US:

• people aged 16 years and over can have the Pfizer vaccine

• people aged 18 years and over can have the Moderna vaccine or the Janssen vaccine.

Children and teenagers

At the start of the vaccination program, the vaccines were only recommended for adults. But the Pfizer vaccine is now being made available in the US for teenagers aged 5 to 15 years.

Pregnant and breastfeeding women

In the US, pregnant and breastfeeding women are encouraged to be vaccinated. Pregnant women are at risk of serious health problems if infected with COVID-19, including preterm birth. Vaccination should reduce these risks.

You might want to talk with your doctor or another healthcare professional about any concerns you have before having the vaccine.

But the decision to be vaccinated is your personal choice. If you’re not happy to have the vaccine, your decision should be respected.

When will I get the vaccine?

Most adults should now have been offered their first doses of the vaccine.

The vaccine is being offered to people based on who needs it most urgently. This means that the first people to get it will usually be:

• people who have the greatest chance of getting COVID-19, and

• those most likely to become seriously ill if they are infected.

For example, some of the first groups of people to be offered the vaccine are likely to be:

• those who live or work in long-term care facilities, and

• frontline healthcare workers.

The next groups of people to be vaccinated will include:

• frontline essential workers, including firefighters, police officers

• people aged over 75 years

• people aged over 65 years, and

• those with underlying medical conditions who would be most likely to have severe symptoms if infected.

Booster shots

Most people will now have been offered a vaccination. For many people, it has been quite a long time since they had their vaccine. And we know that the protection from the vaccines reduces over time.

Because of this, booster shots are now recommended for everyone aged over 18, and many people will have had their booster. These shots top up or "boost" the protection from the vaccines, so that, if infected, you are far less likely to become severely ill.

You can get a booster shot if:

• it is at least six months since your second dose of the Pfizer or Moderna vaccine, or 

• it is at least two months since you had the Janssen vaccine.

  You might need to wait a little longer to have your booster if priority is being given in your area to groups such as older or vulnerable people.

Is there anyone who shouldn’t have the vaccine?

The vaccine is not currently recommended for some groups of people. This doesn’t mean for certain that it’s not safe for them. It just means that we don’t know enough about the new vaccines yet to be absolutely sure.

People with certain allergies

A small number of people have had allergic reactions after having the vaccine.

You should:

• not have the vaccine if you are allergic to any of its ingredients

• tell the health professionals giving you the vaccine about any allergies you have, before you have the shot. He or she will check if these are a problem.

Food allergies should not be a problem. If you have a food allergy you should be able to have the vaccine.

If you have an allergic reaction to the first dose of the vaccine, you should not have the second dose.

People with weakened immune systems

Some medical conditions and some medications can cause the body’s immune system to become weaker. This means that infections can be more serious.

The COVID-19 vaccines don’t contain any live organisms, so they are thought to be safe for people with weakened immune systems (doctors call this being immunocompromised).

But you should mention to the health professional giving you the vaccine if you have a weakened immune system for any reason, before you have the shot.

How safe is the vaccine?

The COVID-19 vaccinations are considered safe. But, like any vaccine and any medication, they can cause side effects in some people. These side effects are usually mild, but some people feel pretty miserable for a few days. The most common side effects are:

• pain, redness, swelling, or bruising in your arm where you have the shot. This can last for a few days

• tiredness

• headache

• fever

• nausea, and

• pain in a joint or muscles.

If you get any side effects they will usually be mild and won’t last more than a few days.

There are some simple things you can do to help with some of the side effects.

• If you have pain in your arm near where you had the shot, keep using and moving the arm so that it doesn’t stiffen up. You could also try an over-the-counter pain reliever, such as acetaminophen or ibuprofen.

• If you have fever, drink plenty of fluids, and dress lightly to keep cool.

If you have severe side effects, or if you have any problems that don’t go away soon after you are vaccinated, tell your doctor or another healthcare professional right away.

Serious problems with blood clots have been reported in a very small number of people given the Janssen vaccine, mainly in women aged below 50 years. These problems are extremely rare, and the benefits of the vaccine are considered to outweigh any risks.

But if you are concerned, talk to your doctor.

After you have the vaccine

Having the vaccine might not stop you from being infected with the virus. But it can reduce your chance of becoming seriously ill with COVID-19.

But the vaccines take time to work. So you might not be protected for up to two weeks after your first dose of the vaccine. The best protection comes after you have had both doses.

Also, vaccinated people who are infected can still pass the virus onto others.

So it’s important to keep doing the things that help keep you and others safe. That means:

• wearing a face covering

• washing your hands carefully and often, and

• practicing social distancing.

For more information on COVID-19, including prevention and treatment, see our leaflet COVID-19 (coronavirus).