Canada has mandatory screening (and treatment) of migrants. AFAIK the US doesn’t but 96% choose to be screened anyway.
https://www.cdc.gov/mmwr/volumes/71/ss/ss7102a1.htm
This isn’t a migrant issue. It’s a homegrown issue. (And if you want to blame foreigners, US citizens seem like a more likely culprit given skyrocketing US rates of infection and poor health care availiability/affordability)
Also, there is no vaccine against syphilis.
This is a sensitive subject, but that’s partly changed thanks to drugs like Truvada and PrEP.
You can now have sex with someone who has HIV and still not contract it. People are having more unprotected sex, safe in the knowledge that they’re on PrEP and they basically can’t contract HIV anymore. Hell, AFAIK you can even take a large dose of PrEP or Truvada AFTER you’ve had risky sex. This is great news. Not having safe sex isn’t. It’s a problem in the gay community.
Important caveat: apparently people are also getting tested more often exactly because HIV is now far more treatable or preventable, which means doctors are diagnosing cases of syphilis which would otherwise have gone undetected (syphillis can often be asymptomatic until it starts causing serious damage):
https://www.cbsnews.com/news/syphilis-rates-gay-bisexual-men/