The old joke that IPO stands for "it's probably overpriced" came to mind last week, following the enormously successful initial public offerings by Airbnb and food delivery company DoorDash.

DoorDash shares almost doubled during Wednesday’s market debut, valuing the loss-making company at $60 billion. As for Airbnb, shares more than doubled following Thursday’s IPO, giving the company a market capitalisation in excess of $100 billion – some comeback for a company that had to raise $2 billion in emergency funding at the height of the pandemic in May.

Airbnb may yet justify investor optimism, assuming people’s appetite for travel resumes following mass vaccination. At the same time, investors seem exuberant about DoorDash’s post-pandemic prospects, even though it’s reasonable to ask if it can keep growing in a very different environment.

David Trainer of New Constructs isn’t a believer, suggesting it is not a coincidence that DoorDash filed for its IPO so soon after Covid-19 vaccines were announced. DoorDash, says Trainer, will be remembered as “the most ridiculous IPO of 2020”.