Why did the Vax Cards have 4 boxes from day one?

Why did the Vax Cards have 4 boxes from day one?
This image is pre May 2021.

I remember thinking "Other" what the hell is "Other" for?

If they only realized they would need boosters in the last couple of months... Why did they print cards with 4 boxes from day one?

What vaccine has ever required 4 doses in the past?

It's almost like... this was the plan all along and they are already set up to give people at least 4 shots.

What was the other section for if they actually thought that 2 doses would be enough to stop the spread?
Updates
+1 y
Please stop saying "boosters make sense". That's fine. That isn't the question. The question is why are the boxes already on the card if they insisted they thought and insisted that they weren't going to add more shots. I'm not asking if boosters make sense. Why were the boxes there if they didn't think they would be nessicary?
Updates
+1 y
Libs literally just parrot back "VIRUSES CHANGE, TRUST THE SCIENCE" Without even understand the question and it gets old. So far nobody had a reasonable explanation for why they were there if the CDC didn't PLAN to change the definition of fully vaccinated from day one. And there are 4. . .
Why did the Vax Cards have 4 boxes from day one?
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