My best guess is no, but feel like I should throw this question out there in case anyone can think of plausible candidates. Most of the advice is targeted to large donors in EA on the assumption that Open Phil, etc is ~40% likely to come across this thread, rather than for scrub small-scale donors like me.
Some possibilities I could think about:
1. Buy testing kits from South Korea/Chinese manufacturers and partner with biohackers/nonprofit groups/homeless shelters/senior homes/other at-risk places to administer them ahead of hospital systems. Understand that you probably can not legally call them COVID-19 tests, but still do this type of guerilla testing quickly and provide necessary quarantine guidelines/supplies later/
2. Fund a large prize for the best #AlternativeVentillator design that balances cost, ease of construction, and quality.
3. Buy ads on New York Times/Fox News etc (and other local equivalents in other countries), to make #flattenthecurve messaging more well-known among people who aren't aggressively online.
4. Prepare and be ready to buy ads on local communities that just got evidence of an outbreak and suggest emergency measures (we may be able to race a few days ahead of public health authorities in acting very fast this way).
(One way to race ahead is to bid a lot for heavily targeted Google and FB ads).
5. Fund vaccine projects (though it looks like a lot of projects are already underway and dumb money might make this situation worse).
6. Fund a large prize for aggressive/fast/cheap testing, potentially to be used in the developing world.
7. Assume Bill Gates knows what he's doing here and throw money at whatever the Gates Foundation throws money at (assuming they have similar policies like Open Phil and don't want to account for 100% of funding for most projects).
8. Buy a lot of masks and distribute it to at-risk populations.
9. Fund studies for various airport interventions.
10. Give a grant or fund a prize for a high-quality no-contact thermometer for humans, to be used at airports, conferences and other places.
Thoughts on additional suggestions? Would especially appreciate ones that have cost-benefit estimates/guesstimates tacked on (would also be excited if someone can formalize any of my loose suggestions into solid cost-benefit guesstimates).
Addendum: Also excited to learn of existing/shovel-ready projects and nonprofits that EAs can fund, not just new projects. However, for those I'd appreciate a specific summary and cost-effectiveness estimate attached (otherwise we'll see a lot of answers that are just stuff like "The Red Cross").