I do not know how different blockchain would be, but as for bitcoin, it is a public ledger that anykne can just make use of blockchain explorer to see transaction records, nothing hidden about it, but just that whaky is already existing on the public as valid would be highly difficult to change which can only occured during 41% attack.
How is a person's computer meant to have enough memory to store all of a country's citizens' medical records if the data is saved on each node in a blockchain?
Like bitcoin blockchain that requires 400 gigabyte, there are 2 terabyte of SSD card or HDD card existing which would be able to do that. Medical record would even need lesser memory space.