As new variants of the coronavirus that causes COVID-19 emerge, a slew of new studies suggest that some may be able to evade immune responses triggered by a previous infection or by a vaccine. That worry has already prompted some vaccine makers to look for ways to tweak their shots to keep up with these troublesome newcomers. Researchers had been concerned that mutations in a viral protein that helps the coronavirus break into cells could dampen the immune response against the virus. The new studies suggest that some viral variants may escape at least some of that immunity, which could put people who have been vaccinated or who have already recovered from a bout of COVID-19 at risk of getting infected.