Here's what to know about the Johnson & Johnson vaccine.
Clinical trials suggest it reduced severe COVID-19 illness by 85 per cent.
It prevented 100 per cent of COVID-related hospitalization or death.
Vaccines from Pfizer, Moderna and Oxford-AstraZeneca also had zero hospitalizations and deaths in their trials.
J&J was 72 per cent effective in preventing COVID infections after 28 days in the company's U.S. trials.
The efficacy dropped to 66 per cent when averaging in results from other trials, including a South African study that factored in more transmissible variants .
Pfizer and Moderna showed 95 per cent efficacy in their trials that were done before new variants emerged .
Johnson & Johnson requires only one dose.
It can be stored in a regular fridge.
Pfizer and Moderna require freezers, but AstraZeneca can be stored in a fridge.
The U.S. FDA said the most common reported side effects were headache and fatigue, followed by muscle aches, nausea and fever