Defence Against Disease · Paper 1 — Free Biology SL Practice Questions

A patient was vaccinated against influenza. The graph of antibody concentration in their blood shows a moderate peak at day 7, a gradual decline, and then a faster, higher peak beginning at day 90 when the patient was naturally exposed to the influenza strain covered by the vaccine. Which statement correctly explains the second peak?

A researcher measures the concentration of antibodies specific to a pathogen in the blood of vaccinated individuals over time. After the initial dose, antibody concentration rises slowly to a low peak. After a booster dose of the same vaccine, antibody concentration rises rapidly to a much higher peak. Which of the following best explains this difference?