This image depicts a Centers for Disease Control and Prevention (CDC) scientist unpacking influenza samples that had been sent to CDC for testing. At this point, the samples were being removed from their temperature-controlled shipping materials. Note that the scientist was wearing protective pink-colored gloves while handling the boxed materials.
Influenza (flu) viruses change constantly. As a WHO Collaborating Center for Influenza (WHO CC) and the U.S. National Influenza Center, CDC monitors flu activity nationally and globally with other labs, looking for changes in circulating viruses. CDC monitors flu viruses because changes can impact the effectiveness of flu vaccine. When circulating viruses are substantially different from those in the vaccine, vaccine effectiveness can be reduced. If it looks like viruses are starting to change in specific ways (which can impact how well the vaccine works), this can trigger health authorities to recommend different viruses for vaccine production.