Influenza causes seasonal outbreaks yearly and unpredictable pandemics with high morbidity and mortality rates.Despite significant efforts to address influenza,it remains a major threat to human public health.This issue is partially due to the lack of antiviral drugs with potent antiviral activity and broad reactivity against all influenza virus strains and the rapid emergence of drug-resistant variants.Moreover,designing a universal influenza vaccine that is sufficiently immunogenic to induce universal antibodies is difficult.Some novel epitopes hidden in the hemagglutinin (HA) trimeric interface have been discovered recently,and a number of antibodies targeting these epitopes have been found to be capable of neutralizing a broad range of influenza isolates.These findings may have important implications for the development of universal influenza vaccines and antiviral drugs.In this review,we focused on the antibodies targeting these newly discovered epitopes in the HA domain of the influenza virus to promote the development of universal anti-influenza antibodies or vaccines and extend the discovery to other viruses with similar conformational changes in envelope proteins.