If Omicron evades immunity acquired from prior infection and two-dose vaccinations (as the early evidence suggests it does), countries that have not yet administered boosters are likely to a see waves larger than those that will be experienced by developed countries with booster programs. The Economist has a nice graphic that shows which countries are best vs. least prepared to face Omicron.
Derek Thompson of The Atlantic describes the issue facing the developing world as follows:
Booster shots aren’t as available to most low-income countries, and the full-vaccination rate across Africa is pitiful. In Cameroon, it’s less than 3 percent. In Nigeria, it’s less than 2 percent. In Chad, it’s less than 1 percent. Even if Omicron is inherently less severe, cases could still overwhelm some of these countries’ hospitals and cause major disruptions.
Unfortunately, Omicron will set back recovery efforts and have adverse effects on a range of development outcomes (nutrition, education, etc). Strengthening disease surveillance, testing and emergency healthcare capacity are among the measures countries should take now to prepare for the coming wave.