As the nation enters its normal flu season amid the COVID-19 pandemic, experts say there's still much unknown about what's to come.
What we do know:
1. Seasonal flu activity in the U.S. is increasing, including indicators that track hospitalizations, according to the CDC. The percentage of visits for respiratory illness reported to the CDC are trending up for all age groups.
2. Since Oct. 3, 3,127 flu cases have been confirmed by public health labs nationwide. In total, 98.1 percent of the cases have been Type A while 1.9 percent have been Type B. Both strains commonly had subtypes circulating during recent flu seasons.
3. For the week ending Dec. 11, 3.5 percent of specimens tested for flu were positive, up from 2.6 percent the previous week.
4. There are early signs that flu vaccination uptake is down this season compared with the 2020-21 season, according to the CDC.
5. Twelve states reported high or moderate flu activity for the week ending Dec. 11, according to data from the CDC's FluView report published Dec. 17. Meanwhile, 19 states reported low flu activity and the remaining states reported minimal flu activity.
6. No pediatric flu deaths have been reported for the 2021-22 flu season. One pediatric flu death was recorded last season.
What we don't know:
7. Although flu numbers last year were significantly lower than normal, pandemic restrictions have relaxed and some experts are warning about a possible "twindemic." It's still too early in the seasonal flu season to predict if the nation has averted the scenario, as the U.S. flu season typically picks up in January.
8. Though researchers still don't know a lot about the coinfection of flu and COVID-19, new studies suggest coinfections of many pathogens might be more common than previously thought.
9. Scientists are exploring whether a common flu strain has gone extinct during the pandemic, though they don't expect to have concrete findings for at least a year. Labs across the globe use genetic sequencing to track the presence of flu strains and upload their findings to an international database. Since early 2020, no labs have reported flu infections caused by the influenza B Yamagata lineage. Researchers are studying Yamagata's potential disappearance, as its extinction could change how drugmakers formulate annual flu shots.