Flu vaccines are safe and effective for most people. However, the usual production method does have disadvantages.
Currently, flu vaccines require a multistep process. To begin with, chicken eggs are inoculated with both the virulent flu virus, and also with a harmless but related virus. The two viruses are allowed to recombine, and the resulting hybrids are tested. The ones that contain the outer proteins from the virulent virus (so the immune system can learn to recognize it) but the inner proteins from the harmless virus (so it can not infect) are chosen for the vaccine. At this point, large scale production can begin, with the vaccine strain of virus grown in more eggs, harvested, purified and inactivated. Over a billion were used for the H1N1’s 3 billion doses.
It’s immediately clear that one liability is the amount of time required to make the vaccine. At best, the process takes five months, and can take much longer. Among other problems, slower than usual viral growth or a shortage of eggs can cause substantial delays. Another drawback is the fact that people who are allergic to eggs cannot use the vaccine.
To circumvent these issues, several labs are studying the use of virus-like particles (VLPs) as a means to make vaccines. These are particles that are similar to viruses because they have protein shell like a virus, but lack components essential for infection. For the purposes of vaccine production, the VLPs do not contain any nucleic acid, but are simply antigenic shells that can trigger an immune response.