That's not universally true. The immune system is far more complex than that. Two examples: 1. 28 year olds, who were exposed to a prior influenza pandemic dur

That's not universally true. The immune system is far more complex than that. Two examples: 1. 28 year olds, who were exposed to a prior influenza pandemic during an early age window, disproportionately died during the 1918 pandemic. https://www.cambridge.org/core/journals/british-actuarial-journal/article/agedependence-of-the-1918-pandemic/3BCBF4BDFBD8C5F0F4FBFDF34DF42209 https://www.cambridge.org/core/journals/british-actuarial-jo... 2. Measles destroys prior immune memory. https://www.nature.com/articles/d41586-019-03324-7 https://www.nature.com/articles/d41586-019-03324-7