The European Medicines Agency (EMA) is expected to make a decision on giving the green light to a fourth coronavirus vaccine on Thursday.
The Amsterdam-based agency is expected to recommend the approval of the jab from US manufacturer Johnson and Johnson.
The European Commission would then have to approve the step, but this is a formality that could take place the same day.
The EU has already ordered doses for 200 million people.
The jab was developed by the company's subsidiary Janssen in the Netherlands.
Unlike the vaccines from Pfizer/BioNtech, Moderna and AstraZeneca that have already been authorized, only one dose of the Johnson and Johnson jab is required.
The doses can also be stored in a standard fridge, unlike the ultra-cold conditions required for some other vaccines.
Effective against variants
A global clinical trial showed the Johnson & Johnson vaccine was 66% effective at preventing various coronavirus variants. It was 85% effective at protecting against severe cases.
It is thought to be effective against virus variants as well.
EMA experts have been analyzing research and test data for weeks as part of a rolling review process.
The EMA will first decide on a conditional market approval. This means the manufacturer will have to continue submitting data about long-term effects after getting the go-ahead.
US regulators formally approved the jab at the end of February.