BY BILL AND MELINDA GATES 2020 has been a hard year to be an optimist. Both of us have spent the past several months looking at alarming charts and datasets. COVID-19, in addition to claiming millions of lives and crashing the global economy, has reversed the progress the world has made in the fight against poverty and disease—a fight in which our foundation is deeply involved. Humankind now must contend with all sorts of numbers that are heading in the wrong direction: Vaccine coverage has dropped to levels not seen since the 1990s. The extreme poverty rate has shot up…