About COVID-19 Vaccine Janssen 

COVID-19 Vaccine Janssen is a single dose vaccine which protects against COVID-19 disease caused by the SARS-CoV-2 virus. 

  • Medsafe COVID-19 vaccine Janssen datasheet
  • Medsafe COVID-19 vaccine Janssen CMI
  • Immunisation Handbook 2020: Cornonavirus disease (COVID-19) chapter

How the vaccine works

COVID-19 Vaccine Janssen is a viral vector vaccine. The vaccine has two key elements. One is a modified human adenovirus (Ad26 – known as a viral vector), which is able to enter human cells but cannot replicate or cause illness. The other element, carried by the viral vector, is the code to make SARS-CoV-2 spike protein. When we receive this vaccine, the modified virus vector instructs our body how to produce copies of the COVID-19 virus (SARS-CoV-2) spike proteins, which in turn, activates our immune system against the COVID-19 virus. If you are then later exposed to the real COVID-19 virus, your body can act quickly to block the virus entering your cells and protect you from illness. This technology is already approved for use for an Ebola vaccine and is similar to COVID-19 Vaccine AstraZeneca. There is no live COVID-19 virus in the vaccine so you cannot get COVID-19 from the vaccine.

For more information on viral vector vaccines please see this video.

Vaccine effectiveness

The effectiveness data for the COVID-19 Vaccine Janssen from both the clinical trials and now from extensive international use are excellent. With confidence, it is effective in preventing against COVID-19. Phase 3 trial data has shown a 66.9% (95% CI: 59.0–73.4%) vaccine efficacy against moderate to severe COVID-19 disease occurring at least 14 days after vaccination. Efficacy was higher at 76.7% (95% CI: 54.6–96.6%) against severe/critical COVID-19 14 days post vaccination. It has also recently been shown to generate ‘strong, persistent activity’ against the delta variant.

Vaccine safety

The safety data for the COVID-19 Vaccine Janssen has been reviewed from both the clinical trials and now from extensive international use and are excellent. The safety profile of the COVID-19 Vaccine Janssen is similar to that of other vaccines given in New Zealand, including Comirnaty (COVID-19 vaccine made by Pfizer). Some people experience discomfort at the injection site on the arm and flu-like symptoms (headache, fatigue, muscle aches, nausea) for just a day or two after vaccination. This is an expected response although is not experienced by everyone.

A rare but serious side effect of blood clots with low levels of platelets (called thrombosis with thrombocytopenia syndrome or TTS) has occurred following vaccination with adenoviral vector vaccines (AstraZeneca and Janssen vaccines). It is most common in women under the age of 50. The incidence of TTS remains very rare (around 7-10 case per million doses) with the benefits of vaccination outweighing this small risk. The ages at which these vaccines are given vary in different countries taking in to account the risks associated with COVID-19 illness. More information is available in this video explaining TTS in more detail.

Vaccine should not be given to:

  • Anyone with severe allergy (anaphylaxis) to a component of the vaccine
  • Administration should be postponed in individuals suffering an acute febrile illness (temperature over 38°C) or who are systemically unwell. The presence of a minor infection is not a reason to delay immunisation.
Last updated: 14 April 2022