“We’ve gone over a year without a significant portion of the population getting infected with flu and getting immunity because of that,” Pekosz said. “That could mean that the susceptible people in the population to flu are going to be increasing.” When someone gets the flu, they usually develop some immunity to the virus. That’s why young children and babies are often the most susceptible to getting infected, because their immune system hasn’t seen the virus yet. But since there was such little influenza circulating this year, the number of people without any prior immunity could double. “With low level population immunity, that could bring about more cases,” said Scott Hensley, a microbiologist at the University of Pennsylvania Perelman School of Medicine. “We could see more pediatric deaths and, concurrent with that, a rise in cases within the whole community. That’s because overall population immunity is predicted to be low.”