Question

During a winter influenza outbreak, not all exposed individuals are infected. Additionally, some infected individuals display only minor symptoms, while others become seriously ill. Discuss how variations within the population affect survival and fitness using an influenza outbreak as a model to support your explanation.

Answer 1

Influenza viruses belong to the family Orthomyxoviridae which causes respiratory infections worldwide. During an influenza outbreak, many people get infected and die. However, a section of the population survives . This happens due to acquired immunity.Immunity may be acquired in a varied range because of many factors which includes variations in the genotype, phenotype , lifestyles, age, environment etc. The population which shows ressitance towards the virus tend to grow and develop , they mature and reproduce to produce registant generations to that particular strain of virus. However viruses keep on mutating with antigen shifts and thus people do not become completely immune from the disease and shows symptoms at varying levels.

There are multiple waves occurring in an influenza pandemic . Here is a note on the influenza pandemic of 1918-19. When it comes to resistance during this time many people in urban locations remained unaffected. The reason behind this can be predicted as pre-existing cross-immunity in the first wave, due to which immunity is acquired in later waves.

During the 1018-19 pandemic, around 24,706 individuals were exposed to the summer, autumn and winter waves in 12 English populations .

It was observed that before the summer wave, there was an estimation that 52% of population were susceptible, remainder being protected by prior immunity, But only 25-66% of exposed and susceptible persons reported symptoms.Although after each wave, 33-65% of protected persons became susceptible again before the next wave, due to waning of immunity or antigenic drift. The rates of prior immunity were less in younger populations (19-59%) than in adult populations (38-66%).