Quote Originally Posted by wiggin View Post
There are two separate concerns here:

1. We have no data on the duration and extent of efficacy between the first and second doses if the second dose is given late. The data is extremely thin in the brief period between the first two doses on a normal schedule (only a handful of events and no ability for long term followup), and nonexistent otherwise. They are using a booster dose for a reason.

2. We have no data on the duration and extent of efficacy of a second dose after an extended delay outside the scope of the original trial. Immunization boosters are not well understood and their timing can be critical depending on e.g. vector design.

So, not only might the people be vulnerable until their second dose is administered, they might be vulnerable after the second dose is administered. They might be fine, too, but we simply don't know. Without data it's speculation.

Indeed it is speculation, but it is well reasoned speculation. Just like emergency authorisation itself - the potential for saving tens of thousands of lives makes it seem worthwhile to try this route during the pandemic.