Overview - Janssen COVID-19 vaccine

Vaccines are the most effective way to prevent infectious diseases. They prepare your immune system (your body's natural defences) to recognise and defend itself against a specific virus.

The Janssen vaccine is also known as 'the Johnson & Johnson vaccine'. Johnson & Johnson are the company that make this vaccine.

You will get this vaccine as an injection in your upper arm.


You will need 1 dose of the Janssen COVID-19 vaccine.

It takes 14 days for the vaccine to work. After this, you have completed your first round of COVID-19 vaccination.

If you have a weak immune system you may need an additional dose of COVID-19 vaccine, at least 2 months after your second dose. This should be followed by a booster if you are over 16.


If you are 16 or older, it's important to get your booster when it is due. Without a booster, you are more at risk of serious illness if you get COVID-19.

If you had the Janssen vaccine, you need to wait at least 3 months before you can get a booster.

You will be offered a single booster dose of either the Moderna vaccine or the Pfizer/BioNTech vaccine.

Read about getting your COVID-19 booster dose


Vaccines teach your immune system 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.

Read more about immunity after the Janssen COVID-19 vaccine


The Janssen COVID-19 vaccine was developed in line with international standards of safety.

It has been tested with thousands of people as part of clinical trials.

Read more about the safety of the Janssen COVID-19 vaccine

Side effects

Like all medicines, vaccines can cause side effects. Most of these side effects are mild to moderate and short-term.

Not everyone gets side effects.

Read more about side effects after the Janssen COVID-19 vaccine

Which vaccine is best

All COVID-19 vaccines give you good protection from severe illness from COVID-19 when you are fully vaccinated. The HSE only uses a vaccine if it meets the required standards of safety and effectiveness.

Pfizer/BioNTech or Moderna are the recommended vaccines for people under the age of 50. This is because of the very rare risk of unusual blood clots with low platelets in people under 50 who get the AstraZeneca or Janssen vaccines.

The Moderna COVID-19 vaccine is only used in adults aged 30 and over in Ireland as per NIAC recommendations.

People under the age of 30 who received a previous dose of Moderna COVID-19 vaccine should receive the Pfizer/BioNTech COVID-19 vaccine as a second or subsequent dose.

If you are pregnant

The Janssen COVID-19 vaccine is not recommended for pregnant women. You will be offered a different vaccine.

Read more about COVID-19 vaccines in pregnancy

If you are breastfeeding

You can get the Janssen COVID-19 vaccine if you are breastfeeding.

It cannot infect your baby with COVID-19.

Read more about COVID-19 vaccines if you are breastfeeding

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

Last updated: 23 December 2021 at 4.10pm

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