Antarctica itself currently has no vaccination requirement. That's an entry rule, and it isn't the same as saying no vaccines are advisable, and it doesn't remove the rules of the countries you travel through to get there. Review your routine immunisations and your whole route with a qualified travel health professional, then check your operator's health protocol again shortly before departure.
Three separate things that get blended together and shouldn't be. Antarctica sets no entry requirement. A clinician may recommend vaccines based on your age, health history and the countries you're visiting. And an operator can impose its own health protocol as a condition of travel. Those are an entry rule, medical advice and a contract term, and they change independently.
On COVID specifically, there's no permanent Antarctica-wide rule. Operators, airlines, ports and public health authorities can impose or change requirements, so check your operator's current protocol rather than relying on what applied last season.
Yellow fever isn't an Antarctica requirement either. It becomes relevant through your wider route, particularly if you're visiting or transiting a risk country before or after the expedition. Recommendations within Argentina vary by province.
A common planning window for a travel clinic is 6 to 8 weeks before departure, earlier if your history is complex or you need a vaccine series. Bring the complete itinerary including transit airports. A clinician can't assess your risk from the word Antarctica alone.