Britain's competition watchdog on Tuesday said it was investigating the planned purchase of US biotech company Alexion by Covid vaccine-maker AstraZeneca in a deal worth $39 billion.

In a brief statement, the Competition and Markets Authority said it was looking at whether the deal would "result in a substantial lessening of competition within any market or markets in the United Kingdom for goods or services".

The planned tie-up, aimed at boosting AstraZeneca's work on immunology, was announced in December as the London-listed company began to roll out the coronavirus vaccine it developed with the University of Oxford.