"I don't think it's a sustainable strategy to ask people to get boosters of the same vaccine every two months or three months. People just aren't going to do it.," he says. "I myself felt awful after I got the second of the third shots."

Perhaps, instead, the goal may need to shift from stopping infections to making sure everyone is protected against severe disease over the long-term.

"Could we get to the point where public health officials recommend a shot once a year," Bhattacharya says. "I think that's fairly likely. Now, whether everyone will absolutely need that shot to prevent severe disease each year, that's a different question, and we'll have to wait for the data. I think it's possible that yearly shots won't be absolutely essential for everyone."