How a vaccine teaches the body to remember · Grades 10–12

The passage and its 7 questions

Directions: Read the passage carefully. Then answer the questions in full sentences.

• Every time a new germ enters your body, your immune system faces a problem: it has never seen this invader before. The first line of defense, the innate immune system, attacks anything that looks foreign, sending phagocytes to engulf invaders and triggering inflammation. But the most precise weapons, antibodies shaped to fit one particular germ, take time to produce. During a first infection, the adaptive immune system can take a week or more to ramp up, and in that time a pathogen can make a person seriously ill.
• The adaptive response works by selection. Your body holds millions of different B cells and T cells, each with receptors of a slightly different shape. When one happens to fit an antigen on the invader, that cell is activated and multiplies rapidly. Some descendants of an activated B cell become plasma cells that pour out antibodies, while some B and T cells become memory cells that can last for years or even decades. If the same germ returns, memory cells recognize it at once, and the response is often so fast that the person never feels sick.
• A vaccine builds this memory without the danger of the disease. The idea began with an observation: milkmaids who had caught cowpox, a mild disease, seemed protected from smallpox. In 1796, the English doctor Edward Jenner tested this by deliberately giving a boy cowpox and later exposing him to smallpox, which did not make him ill.
• The word vaccine comes from vacca, Latin for cow. An experiment like Jenner's would never pass an ethics review today, but it began a field that eventually wiped out smallpox, declared eradicated in 1980.
• Modern vaccines present antigens in different ways. Some use weakened or inactivated germs; others contain only a single harmless protein. Messenger RNA vaccines, first approved for wide use in 2020, deliver instructions that let your own cells briefly make a harmless viral protein. The mRNA never enters the nucleus, where DNA is kept, and it breaks down within days, but the immune system has seen enough to build memory.
• Vaccines also protect people who are not vaccinated. When most of a community is immune, a pathogen struggles to find new hosts, and chains of infection break. This herd immunity shields newborns and people with weakened immune systems who cannot safely receive certain vaccines. A single injection is both personal protection and a quiet act of public health.
• 1. Why can a first infection make someone seriously ill before the adaptive immune system responds?
• 2. Explain the role of memory cells.
• 3. What does "eradicated" mean in paragraph 3?
• 4. Copy the sentence that addresses the worry that mRNA vaccines change a person's
• DNA.
• 5. Why does the author say Jenner's experiment would never pass an ethics review today?
• 6. How can vaccinating most people protect someone who cannot be vaccinated?
• 7. Write a counterargument or alternative view and respond to it.