Antigenic Drift
Antigenic drift refers to the gradual accumulation of small genetic changes in a virus over time, leading to the emergence of new strains. This process is particularly relevant in the context of influenza viruses, where it can result in reduced effectiveness of vaccines. Antigenic drift is a key factor contributing to the need for regular updates to flu vaccines to ensure continued protection.
3 Key excerpts on "Antigenic Drift"
eBook - ePub- Irina Kiseleva, Natalie Larionova(Authors)
- 2021(Publication Date)
- Bentham Science Publishers(Publisher)
...Circulating influenza B viruses belong to two major genetically distinct lineages (B/Victoria and B/Yamagata) (for more details, see Chapter 3). Influenza viruses evolve through the gradual accumulation of mutations, which is a molecular basis of Antigenic Drift and genome reassortment (a phenomenon called antigenic shift). New drifted antigenic variants of H3N2 viruses appear every 2–5 years. In contrast, new antigenic variants of H1N1 or influenza B viruses appear less frequently (3–8 years) [ 18 - 20 ]. Reassortment is also of evolutionary importance. Although most new genomic constellations will be unviable or deleterious, some of them may facilitate adaptation to new hosts, help evade host immune responses, and assist in the development of drug-resistance [ 11 ]. Reassortants of human, swine, or avian influenza viruses were detected [ 21, 22 ]. For instance, in 2010-2011, influenza H3N2 variant viruses (H3N2v) with the matrix (M) gene from the 2009 H1N1 pandemic virus were first identified in pigs and humans. Genetically distinct lineages of influenza virus B can co-circulate in the population and reassort [ 23, 24 ]. One of the most famous reassortants is the triple-reassortant that caused the 2009 pandemic [ 25 ]. Escaping from the Immune Response Infection with an influenza virus induces innate and adaptive immune responses. The high variability of HA allows influenza viruses to escape from host immune surveillance and results in seasonal outbreaks. Viruses use various strategies to evade immune responses, resulting in the reduced clearing of the virus and virus-infected cells [ 26 ]. The evasion of influenza viruses from innate and adaptive immune responses reduces the effectiveness of vaccination. Escape immunity allows the virus to reinfect individuals who were once immune to the virus and necessitating reformulation of the seasonal influenza virus vaccine [ 27 ]. Vaccine formulations need to be updated every year to provide adequate protection...
eBook - ePubFrom Killer To Common Cold
Herd Protection and the Transitional Phase of Covid-19
- David M Graham(Author)
- 2020(Publication Date)
- FiPhysician(Publisher)
...At the very minimum, there should be some cross reactivity or partial immunity to any drifted strain. Instead of drifting to evade the immune system, the problem with coronavirus is that immunity to it is not long lasting. In 6-24 months, despite having a perfectly adequate initial immune response, you might get the same virus again as your immunity wanes. Thus, drift is not the issue with relapsing Covid-19 infections, but rather, loss of immunity. Immunity to influenza, on the other hand, can be extremely long lasting. In fact, when H1N1 returned in 2009, those who had it when it last circulated in the 1960’s were usually still immune. Thus, the elderly, despite their weakened immune systems due to normal aging, were relatively protected from H1N1. Unlike coronavirus, influenza may evoke long-lasting immunity after infection. While Antigenic Drift causes seasonal influenza as the virus slowly mutates over time, antigenic shift causes pandemics of influenza. Antigenic shift is a major genetic change that usually involves the reassortment of influenza from another animal species. There are non-human animals that carry influenza—most commonly pigs and birds. What if human and bird influenza strains co-infect a pig simultaneously and the virus recombines? The pig might start producing humanized bird strains of influenza. These recombinant strains pass back to a human, and if effective human-to-human transmission occurs, a new influenza pandemic begins. Antigenic shift is reflected by the H and N monikers of influenza. For example, H1 and H3 correspond to human pathogens currently, while H5 and H7 correspond to bird pathogens. The N can be different as well, as in N1, or N9. H and N are important functional proteins influenza carries that allow us to specifically identify them. If influenza swaps out its human H1 for a bird one, then a virus for which there is no baseline immunity may be born...
eBook - ePub- Phoebe Lostroh(Author)
- 2019(Publication Date)
- Garland Science(Publisher)
...This genome configuration makes it possible for two different influenza viruses to co-infect the same cell and have recombinant offspring with a new combination of genome segments, which is the origin of most pandemic influenza strains (see Chapter 17). Both of these forms of genetic variation are problematic for vaccine development. Moreover, every year manufacturers produce about 500 million doses of vaccine, so that the sheer volume of vaccine required means that vaccine manufacturers must begin many months before flu season. Vaccine manufacturers make an educated guess about which forms of influenza will be circulating during the following flu season. Sometimes their guess is on target, but other times there is a mismatch between the vaccine and the most prevalent form of influenza in any given year. This situation can even cause the alarming effect of discouraging the public from getting vaccinated at all. Figure 16.7 Antigenic proteins of influenza A virus. The two spikes are hemagglutinin (HA) and neuraminidase (NA). In addition to the eight genome vRNPs, the virion contains proteins NP, M1, M2, NEP, PA, PB1, and PB2. Influenza vaccines often provoke a strong antibody response against HA and NA; vaccines in development may also employ the M2 protein. Available anti-influenza drugs target the NA and M2 proteins. It is also possible for influenza to jump from animals to humans. When this occurs, the zoonotic influenza strain is at first not adapted to humans. Although at first it may seem like such a virus would be unable to replicate in humans, sometimes the opposite is true and instead the virus replicates so ferociously that the death rate is much higher than it is for human-adapted influenza strains. H5N1 avian influenza is an example. It has a 60% mortality rate in people but can only be contracted directly from birds; it cannot be transmitted from human to human...
