Matthew Woodruff

By almost any measure, the vaccination campaign against SARS-CoV-2, the virus that causes COVID-19, has been a global success.

As of January 2023, more than 12 billion vaccines against SARS-CoV-2 have been administered in an effort that has saved countless lives more than 14 million in the first year of vaccine availability alone. With a 95% efficacy in the prevention of severe infection and death, and better safety profiles than similar historically effective vaccines, the biomedical community hoped that a combination of vaccination and natural immunity might bring the pandemic to a relatively quick end.

But the emergence of new viral variants, particularly omicron and its array of subvariants, upended those expectations. The latest omicron strain, XBB.1.5. dubbed Kraken, after a mythical sea creature has rapidly become the dominant subvariant in the U.S. The World Health Organization is calling it the most contagious strain so far, with its success almost certainly attributable to an ability to dodge immunity from previous vaccines or infections.