As SARS-CoV-2, the coronavirus that causes COVID-19, has spread throughout the world, many observers have failed to take note of the millions of illnesses and deaths caused by HIV—another virus that has approached pandemic status during its history. Now an HIV variant that is more virulent and transmissible has been discovered in the Netherlands, where it apparently has been circulating for decades, according to new research. Luckily, none of the variant’s new mutations make it resistant to widely used therapies. But the finding may offer a warning for how the COVID pandemic could proceed in the coming months: viruses do...