Immunity - Janssen COVID-19 vaccine

Vaccines teach your immune system (your body's natural defences) how to protect you from diseases.

It is much safer for your immune system to learn how to protect you from COVID-19 through vaccination than by catching the virus.

You will need 1 dose of this vaccine for your first round of vaccination.

Everyone aged 16 and over is recommended a booster dose to extend the protection of your vaccine.

Booster dose

You will be offered either the Pfizer or Moderna vaccine as your booster dose.

These are mRNA vaccines. If you are not able to get an mRNA vaccine, you may be able to get a booster dose of a different vaccine, such as the Janssen vaccine. You will get a benefit-risk assessment to see which option is best for you.

We do not know yet how long immunity will last after boosters. Clinical trials are ongoing to find this out.

Protection from COVID-19

You can still get COVID-19 after vaccination. But being vaccinated can reduce how serious your symptoms will be.

There is some new evidence to show that the vaccines may reduce you spreading COVID-19 to other people but more research is needed.

The HSE, Department of Health and the World Health Organization recommends that you get vaccinated against COVID-19.

Even after you are vaccinated with your first round and booster, continue to follow public health advice on how to stop the spread of COVID-19. For example, social distancing, wearing a face covering and washing your hands properly and often.

Read more about how you can protect yourself and others from COVID-19

Testing and evidence

Worldwide, vaccines save at least 2 to 3 million lives each year. They protect many more from lifelong illnesses. Millions of people have now received COVID-19 vaccines all over the world.

There is strong, reliable evidence that COVID-19 vaccines greatly reduce your risk of getting COVID-19.

They’re highly effective at preventing deaths and serious illness with COVID-19.

If you take immunosuppressive medicines

If you have a weakened immune system, your COVID-19 vaccine may not work as well for you. But there is no extra risk in getting it.

Read more about weak immune systems and COVID-19

If you had a weak immune system at the time of your initial course of COVID-19 vaccination, you may be offered an additional COVID-19 vaccine dose.


This content was fact checked by vaccine experts working in Ireland.

Last updated: 22 December 2021 at 12.30pm

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