With a COVID-19 vaccine here, governments are scrambling to meet the financial and logistical challenge of immunizing their populations in a short space of time. Hopes for a pickup in global economic growth next year depend on it.

But the bigger challenge may end up being psychological: How to convince people to actually take the shot. Achieving herd immunity may mean at least 80% of people will need the vaccine, leaving little room for error.

Polls suggest it’s France, the birthplace of vaccine pioneer Louis Pasteur, that will be the country to watch. A recent Ipsos survey found that only 54% of French adults would be willing to get a COVID-19 vaccine when it’s available, the lowest score of 15 countries. (The U.S. was second-to-last.)