Immunity against Omicron from breakthrough infection could be a matter of timing

Good timing is a key to success — even for riding out the Omicron wave. Research from Japan suggests that COVID-19 vaccination followed months later by a breakthrough SARS-CoV-2 infection offers greater protection against the Omicron variant than do closely spaced vaccination and infection. The finding implies that countries that saw large numbers of non-Omicron infections in late 2021 have an advantage as 2022 rolls in with the new variant. The study has not yet been peer reviewed. Many countries’ populations have gained immunity through a combination of vaccination and infection with an array of variants. But Japan’s population is protected mainly by vaccination with mRNA vaccines. Study co-author Takeshi Arashiro, an infectious disease researcher at Japan’s National Institute of Infectious Diseases in Tokyo, and his colleagues wanted to understand whether the country’s mostly single-source immunity would leave the population especially susceptible to Omicron. So far, the country has had few breakthrough cases, but...