This argument for caution against boosters is badly flawed. They are using pre-delta data to argue it’s inconclusive if boosters are needed against the delta-

https://mobile.twitter.com/michaelzlin/status/14380883906967...

A lot of these arguments seem to be strategic rather than scientific. Many people want to see wider vaccinations worldwide before anyone gets a booster, so they downplay evidence boosters are effective in order to steer people toward their preferred policies.