World should learn the right lessons from India's Covid-19 cataclysm

All nations should now understand that vaccines work and that interfering with their supply is dangerous.

In cities at least, India’s nightmarish second wave of Covid-19 finally seems to be ebbing. Delhi has brought its test positivity rate below 2% for the first time in two months. The pandemic’s scars won’t be easily erased, however — and they should be a warning to other developing nations. Those countries must learn from India’s experience if they don’t want to repeat it. 

The first and most obvious lesson is to avoid overconfidence. A relatively small change in how transmissible the novel coronavirus is can have large, non-linear effects on how fast it spreads. That means strategies that kept