“流感一倒倒一片！”热搜上的K毒株是什么？现在打疫苗还来得及吗？

Core Viewpoint - This year's flu season is unusual, arriving early and exhibiting a more severe impact compared to previous years, with a significant increase in infections among the population [1][3]. Group 1: Virus Characteristics - The "K strain" is not a new virus but a variant of the H3N2 influenza virus, which has undergone minor mutations, making it more adept at evading the immune system [3][4]. - The H3N2 strain has become the dominant virus this season, accounting for over 95% of cases, while H1N1 and B strains have nearly disappeared [4]. - The mutations in the H3N2 strain have increased its ability to adhere to human respiratory cells by approximately 1.8 times compared to previous strains, facilitating rapid transmission in group settings [4][5]. Group 2: Co-circulating Viruses - Multiple respiratory viruses, including RSV and adenoviruses, are also circulating, leading to compounded infections where individuals may recover from one virus only to be infected by another [5]. - The presence of the K strain does not necessarily lead to more severe symptoms compared to other flu strains, but the speed of onset and overall symptoms may be more pronounced [5]. Group 3: Vaccine Efficacy - The current flu vaccines, both trivalent and quadrivalent, are effective against the H3N2 strain and the K variant, providing significant protection against severe illness [6][7]. - Vaccination rates in China are low, at around 3%, compared to 40-50% in developed countries, which hampers the establishment of herd immunity [7]. - Vaccination is still valuable even if individuals have been exposed to the virus, as long as they are not in the acute phase of illness [7]. Group 4: Current Situation and Recommendations - As of December 2025, flu activity is showing signs of decline, but the risk of rebound remains, necessitating continued vigilance in flu prevention [8].