Got letter in the mail from Curative (COVID testing/vaccine company) asking for my insurance information

I got my COVID vaccination on 5/5/2021 (a year and a half ago).

I just recently got a letter in the mail (12/14/2022) from Curative asking for my insurance information.

The letter states:
“At the time your COVID-19 vaccination was performed you either provided invalid insurance information or no insurance information. CURATIVE MED ASSOCIATES PA needs correct and valid insurance information for date of service 5/5/2021 from you in order to submit this claim to your insurance for payment.”

I have a few concerns:

Curative, for whatever reason, decided to wait a year and half after the date of service to contact me. I am no longer with the insurance company I had during the date of service. So if they contact the insurance company I had during the date of service, will I be the one footing the bill?

During this time, the US government was funding COVID vaccines. Why are they trying to bill my insurance instead of the US government? Again, I’m just worried the bill will find its way back to me.

Can I just ignore this letter?

Your inputs would be greatly appreciated.