The swift development of effective vaccines against COVID-19 was an unprecedented scientific achievement. But production challenges, vaccine nationalism, and new variants have all presented hurdles.

Here’s how different health-care systems, including single-payer and government-run, have contended with the coronavirus.

The U.S. health agency regulates the country’s foods and drugs, among other products. The COVID-19 pandemic and controversy over vaccines and treatments have highlighted the FDA’s role.