In order to test whether the flu virus in a sample taken from a patient matches an influenza vaccine virus, the sample needs to be grown in a cell culture, or an embryonated chicken egg. Growing the virus in cell culture or eggs, produces a larger volume and concentration of virus than what was in the original sample. The larger volume of flu virus is needed for additional laboratory tests. In this case, this Centers for Disease Control and Prevention (CDC) scientist was in the process of using a small needle in order to puncture a hole in the top of each of these embryonated chicken eggs. A syringe will then be inserted into the hole, and inject influenza virus into a specific cavity (a sac) inside the egg. There the influenza virus will grow and multiply.
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.
Please visit the link below for more information about Influenza (Flu).