It's incorrect to assume that the information you heard is 100% an accurate representation of the scientific understanding and not information filtered through "public health" which balances that with other interests. I'm not aware specifically what was known at the time about the initial vaccine formulation, but there are several examples where there was a disconnect:

- ~Feb 2020: COVID is known to spread through and linger in the air, not just spread via droplets or fomites; public health messaging fixated on simultaneous 6ft distancing and surface cleaning rather than air filtration and masking

- Spring 2020: it's known that masks reduce the risk of acquiring and spreading infection; in the US, public health messaging stated the opposite, in order to keep as many masks in supply to healthcare workers despite a major shortage of masks

- Jan 2022: it's know that an infected person can remain contagious for over two weeks; in the US, public health isolation guidelines are reduced to 5 days due to noncompliance and in response to pressure from the airline industry, which was experiencing a significant shortage of flight staff due to COVID infection

> why most of their predictions were wrong?

Citation needed.