While I think it's a nice flavor event and that does add a late-game challenge, it feels less like something that forces me to make interesting/hard choices and more of a mana debuff that simply derails my game.
I just played a communist Yugoslavia, and I had a nice balanced economy. Then the flu struck (I got -50% throughput penalties compared to the OPs -25% - does the penalty increase with later waves?) and stayed for about a decade. During that time I tried to mitigate the pandemic's effects on my economy, which was not particularly fun because all I could do was the pandemic decision. After the flu pandemic was over, my economy and the bureaucracy was horribly unbalanced (I suddenly had a 3.5k bureaucracy surplus, so I guess the throughput bonus also affected the government administration buildings and I overbuilt to compensate, because I had a huge amount of tax waste during the pandemic). By that time, it was the late 20s, and I just decided to let the game run until my 95% literacy rate achievement fired.
I'm all for the chance of a late-game pandemic, but until it has been fleshed out or balanced a bit, I'd be more than happy with a game rule to tone it down a bit.
Some ideas for a pandemic rework:
- instead of the flat throughput penalties to all buildings, it the pandemic should affect the pillars of your economy/society and thus indirectly affect your economy. The pandemic could increase mortality and radicals while reducing army morale and limiting the effects of the education institution (schools closed) and research progress (universities closed).
- Some places (like Australia) also had maritime quarantines. This could slow down or bring to a halt migration and give a penalty to trading (either in volume or reduce the profitability of trade routes due to the increased cost of trading). Potentially, the pandemic response decision could allow you to prioritize some measures and result in different combinations of debuffs (maybe you prefer to close educational institutions over limiting your trade, maybe it's the other way round).
- Institutions should matter. In addition to your educational institutions (and depending on whether you close them or keep them open), health care should matter more. It should also make a difference if you have censorship (maybe it reduces the negative effects on army morale at the cost of increased mortality).
- Different sectors of the economy should be affected in different ways. A paper linked in the Spanish flu wikipedia entry mentions that "businesses that specialized in health care products experienced an increase in revenues" (this paper, p.21). While this will only work once the pharmaceutical industry has been added to the game, maybe a stop-gap implemantation could be a chemical plant PM that diverts opium from the military to the civilian sector to reduce mortality.
All these effects would without a doubt affect your economy, but not by applying a direct penalty to it but rather by affecting all the building blocks of your economy: your population, your institutions, your trade relations, and so on. Then you can make hard and interesting choices. And it could also reshape your country: maybe the pandemic resulted in a health care institution, which will now benefit your citizens even after the pandemic is over (and maybe they get angry if you try to decrease health care spending again).
TLDR; the pandemic should have potentially devastating effects on your economy and society, but it should not be a flat throughput debuff but rather affect the underlying factors of your economy (institutions, trade, etc.).
EDIT: I've
opened a thread in the suggestions forum, feel free to chip in!