While my government website says otherwise, I'm just wondering what other travelers experiences would be. Currently traveling through Peru, Bolivia, Chile and then will be going from Paraguay into the Foz de Iguacu on the Brazilian side. I am actually vaccinated for Yellow Fever but I don't have my certificate with me (stupidly forgot it at home). Just want to make sure I won't have any issues with this at the border crossing. Thanks in advance for any info!
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I recall needing one as a citizen two years ago.
Do you have a CDC yellow booklet? It might say there.

I have never been asked for it upon return to Brazil, not once. Even from other countries where YF is endemic.

Brazil does not require the certificate (they already have endemic YF so are not worried about imports) but a lot of countries will require it if you are coming from Brazil
https://www.who.int/ith/ith-country-list-new.pdf

Thanks. I just realized that I'll be in Paraguay beforehand, and they might actually ask me for it! Anyone have any ideas about that?

Thanks. I just realized that I'll be in Paraguay beforehand, and they might actually ask me for it! Anyone have any ideas about that?
It depends on where you have been in the week or two (the incubation period for YF) before you arrive in Paraguay. As the WHO states:
PARAGUAY
Yellow fever (2019)
Country requirement at entry: a yellow fever vaccination certificate is required for travellers aged 1 year
or over arriving from countries with risk of yellow fever transmission.
