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.

We do not know yet how long immunity will last. Clinical trials are happening now to find this out.

How long it takes to work

You will need 1 dose of the Janssen COVID-19 vaccine to get long-lasting protection.

It takes 14 days after getting your vaccine for it to work. This is when you are fully vaccinated.

Protection from COVID-19

There is a small chance you might still get COVID-19 after vaccination. Even if you do get COVID-19, being vaccinated can reduce how serious your symptoms will be.

We do not know yet if having the vaccine stops you from spreading the COVID-19 virus to other people.

Continue to follow public health advice to stop the spread of COVID-19 after you are vaccinated. 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


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

Last updated: 21 May 2021 at 10.10am