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. It will only take a few minutes.
You will need 1 dose of the Janssen COVID-19 vaccine to get long-lasting protection.
It takes 14 days for the vaccine to work. This is when you are fully vaccinated.
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.
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.
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.
Getting your vaccine
Most people will be vaccinated at a GP surgery or a vaccination centre.
But people aged 18 to 34 can get a Janssen COVID-19 vaccine in a pharmacy. You do not need to register online. But you do need to book an appointment through a participating pharmacy.
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.
But, because there is a greater risk of infection from newer variants of COVID-19, it's more important than ever to get vaccinated.
If you are aged 18 to 34 you can choose to opt in for the AstraZeneca or Janssen vaccines. This means you may get vaccinated earlier.
If you are pregnant
The Janssen COVID-19 vaccine is not recommended for pregnant women. You will be offered a different vaccine.
Talk to your GP or obstetrician about getting your COVID-19 vaccine.
If you are breastfeeding
You can get the Janssen COVID-19 vaccine if you are breastfeeding.
It cannot infect your baby with COVID-19.
This content was fact checked by vaccine experts working in Ireland.
Last updated: 15 July 2021 at 10.20am