How did Pfizer measure the efficacy of the vaccine in children | Covid and Kids

How did Pfizer measure the efficacy of the vaccine in children? Let's review:

They measured the blood of 264 children for antibodies.
There were 3,000 vaccinated children in the trial. What about the other 2,700-plus being measured for antibodies?

It should also be noted that Pfizer enrolled children in the trial who had previous covid infections. This means, children who would already have antibodies because they already had covid.

They are using the data from less than 10% to decide that it’s efficacious to vaccinate tens of millions of children across the US and likely in Canada too.

Additionally, there is zero long term safety data. The trial won’t have final results until January 2024. https://clinicaltrials.gov/ct2/show/record/NCT04816643?view=record

I would like to remind you that vaccine manufacturers are immune from any liability. This is a major red flag so they can’t be sued even if they are negligent. Pfizer is notorious for being negligent - manipulating data and making fraudulent claims. They have the distinction of the biggest criminal payout in history.