What might account for the fact that developed countries were more affected than developing countries during the h1n1 pandemic?

Free market is a characteristic mostly found in rich countries and those that are both rich and developed have strong economic relations with many other countries, which increases the amount of travels in and out of those countries. Not only that, a richer population also travels more for they have more money to spend with vacations. Generally speaking, it is more common for people of developed countries to leave their cities and countries than for people in developing nations because those many times barely have money to pay their rent.

This economic factor that affects travels is what cause developed nations to be more affected by H1N1 for they had a lot more people coming in and out of the countries.

2018 means 2018 ce or common era

there have been other eras too including bce, which included way more years.