I suppose the only way it could have been prevented would be knowing in advance what would happen in case of contact, having the self restraint to not allow any

I suppose the only way it could have been prevented would be knowing in advance what would happen in case of contact, having the self restraint to not allow any intrusion and to spread vaccines. Ie. having our current technology. But really it seems like it would have happened whenever American population centers contacted more than a dozen Eurasians.