A new pair of studies take a look at the human immune response to the flu vaccine and explain how the flu components may affect the shot’s effectiveness.
From season to season the flu vaccine varies in effectiveness; this is one of the challenges of trying to hit a moving target that is always changing. Now, a pair of recent studies suggests that the conventional flu vaccine can be improved to become more effective at preventing the virus.
Through global programs such as the World Health Organization’s (WHO) Global Influenza Programme, along with national flu surveillance from the Centers for Disease Control and Prevention (CDC) and other national and local agencies, health officials are able to monitor flu activity around the world. The data they collect on virus trends informs outbreak monitoring and tracks the “antigenic drift” and “antigenic shift” that continually create changes in the genes of influenza viruses. WHO’s Collaborating Centers for Reference and Research on Influenza, a global advisory group, use the aforementioned data to make recommendations for each season’s flu vaccine for the Northern and Southern Hemispheres to protect against the viruses that are most likely to spread and cause illness.
When the flu vaccine works, it can effectively prevent illness, missed work days, hospitalization, medical expenses, and even death. Health officials are quick to tout the benefits of the seasonal flu shot as well as it’s proven record of success while acknowledging that it’s not perfect. Recently, two studies published in the journal Nature Medicine looked at the effectiveness of flu vaccines. The first study, led by researchers at the University of Texas at Austin, investigated the benefits of a trivalent flu vaccine that protects against three viruses rather than the currently recommended quadrivalent vaccine that is designed to protect against four virus strains. In a case of “more is not necessarily better,” the team found that the benefits of the quadrivalent vaccine were not significantly greater than the trivalent vaccine.
Using a new technology called Ig-Seq, the researchers were able to directly identify and quantify antibodies produced in response to flu vaccination to observe how the vaccine activates the immune system response. They studied antibodies in young adults before and after receiving a flu shot and observed that just about 40% of influenza-specific antibodies came as a result of vaccination, with the rest being antibodies that were already present in the bodies of the vaccinated. When comparing trivalent to quadrivalent vaccines, they also noted that 90% of antibodies educed by one virus in a trivalent vaccine were also able to bind to the fourth virus component in a quadrivalent vaccine, showing that the extra viral strain does not produce a considerable additional antibody response.
“In order to develop a better vaccine, you need to have a more precise, better understanding of the current vaccine’s efficacy, and to do that you need to identify the individual antibodies that specifically bind to influenza, understand how they protect from disease and measure how long they can persist in circulation,” explained first author and Cockrell School chemical engineering doctoral student, Jiwon Lee, in a recent press release. The team hopes their research leads to a more effective flu vaccine.
In addition to these findings, a collaborative study lead by Harvard University researchers looked at the way vaccines are produced and how this may impact flu shot effectiveness. The majority of flu vaccines are egg-based, containing candidate vaccine viruses that are grown in eggs and then injected into fertilized eggs, where the viruses incubate for several days and are able to replicate. The fluid containing the virus is then extracted and the viruses get inactivated for the vaccines; the production of each vaccine dose requires about one egg. These common vaccines are not recommended for individuals with egg allergies. The other flu vaccine production processes use animal cell-based methods that do not require the use of eggs to incubate the virus, but consist of a recombinant technology process using insect cells.
Under investigation in this study were egg-based flu vaccines, which the team found cause the human immune system to partially produce antibodies with an avian receptor preference. Vaccines that don’t use avian cells may be more effective at producing broadly-neutralizing antibodies than egg-based vaccines, and thus, prove to be more effective at preventing illness. “The implication here is that the production of the vaccine in eggs can detract from its utility in eliciting a protective immune response in humans,” said study author George Georgiou in the press release.
CDC officials have noted that based on current surveillance they expect the flu vaccine for the 2016-2017 season to effectively protect individuals from the currently circulating viruses, and recommend receiving the shot in order to prevent getting sick with the flu this season.