The four main drug companies making COVID-19 vaccines have sold a combined $18.6 billion worth of the shots in the first half of 2021, and sales are expected to reach a combined $60 billion by the end of the year.

The big picture: Even though the U.S. represents less than 5% of the global population, the U.S. market makes up 41% of the vaccine sales.

Between the lines: Vaccine makers have sent more vaccines and charged higher prices to wealthy countries, including the U.S. The higher prices are part of the reason Pfizer and Moderna have advocated for booster shots even though their vaccines remain very effective after six months and against the Delta variant.

• The World Health Organization has called for a moratorium on boosters so more unvaccinated people in low-income countries can get their first shots.

By the numbers: Pfizer and Moderna have collected more than 90% of global COVID-19 vaccine revenues.

• Pfizer alone accounts for 60% of worldwide sales. Moderna's two-dose vaccine, which was 100% funded by the federal government, has more than half of its sales in the U.S.
• Johnson & Johnson's one-shot vaccine hasn't sold nearly as much due to safety concerns, but the company still expects $2.5 billion of global sales this year based on its advanced purchasing agreements.
• The FDA still hasn't authorized AstraZeneca's shot for use in the U.S. The company hopes it will before the end of the year. AstraZeneca has been selling its shot at a not-for-profit price.