Influenza Vaccine Affectiveness

Influenza Vaccine Effectiveness

The flu is a contagious disease that that affects 5%-20% of Americans each year caused by influenza viruses (Anon., 2017). symptoms of the flu can be mild or severe depending on the status of infected individuals. Untreated flu can lead to complications such as pneumonia, sinus infection, and ultimately, death. Luckily, our bodies have the ability to fight against these viruses through our immune system, and it is important to get vaccinated yearly to further increase our chances against the virus.

The immune system refers to the network of cells and biological structures in our bodies that are in charge of warding off or suppressing any disease-causing agents. The defense can be adaptive or innate. Innate immunity refers to the body’s automatic response to attack any foreign agents (antigens), this ability is present at birth (Anderson et al, 2016). Adaptive immunity developed throughout lifetime through the body’s exposure to specific types of microbes or antigens, thus improving the host’s defense system (Anderson et al, 2016). The immune system’s initial response to an antigen is called the primary immune response, where the system encounters the antigen for the first time. Vaccines can simulate the infection with a weaker version of the antigen/pathogen, triggering the primary immune response. After the primary immune response, the body gains 'memory cells' that will respond quicker to the same antigen/pathogen, this is referred to as the secondary immune response (Anon., 2013).

Influenza viruses are extremely versatile because of their ever-changing nature. Therefore, there is no universal vaccine to prevent the flu. There are four types of influenza virus: A, B, C and D. Influenza A and B are known to cause illness in humans during their seasonal epidemics, with type A being the most diverse with its subtypes (Anon., 2018a). In influenza B, there are two lineages instead of subtypes and current active influenza B virus belong to one of these two lineages: B/Yamagata and B/Victoria. Influenza A consists of different subtypes due to frequent changes in their gene, examples of these subtypes are: Influenza A (H3N2) and influenza A (H1N1) (Anon., 2018a). Influenza viruses change constantly either by antigenic drift or antigenic shift. Antigenic drift refers to the small changes of the viruses’ gene overtime; influenza viruses experience antigenic drift constantly, and the offsprings often share the similar antigenic properties, thus any immune systems that are familiar with such properties will be able to attack it. However, these changes in the gene can accumulate over time, resulting in new subtypes of these viruses with completely different antigenic properties that our immune systems may not recognize (Anon., 2018b). Antigenic shift refers to abrupt changes that create new hemagglutinin and/or hemagglutinin and neuraminidase proteins in influenza viruses; this type of change only happens occasionally. One example of antigenic shift is the influenza A (H1N1) virus that went through a “shift” in 2009, resulting in a new version of H1N1, called the “2009 H1N1”, that caused a pandemic (Anon., 2018b). No vaccine or protection was available due to the unpredictable nature of the shift.

The most effective way to prevent the flu is to vaccinate. However, influenza vaccines are not always 100% effective against influenza B and influenza A H1N1 and they are way less effective against influenza A H3N2. Of course, besides factors like the virus’s changing nature, the receiver's age and health and the vaccine itself (Anon., 2018c). There is also another factor that affects vaccine effectiveness. It is the frequency of taking the same vaccine. One way that scientists would use to determine the vaccine effectiveness for each flu season is through antigenic distance hypothesis which is determined by the antigenic distance between the vaccine and the virus strain (Danuta et al, 2017). A study was conducted by Danuta et al in 2017 to test the ADH by looking for negative interference from the last season’s influenza vaccine on the current season’s vaccine. The subjects were the medically ill influenza A (H3N2) patients (cases)