In the article “first flu affects lifetime risk” by Caroline Parkinson it explains that there are over eighteen kinds of flu and person falling sick from a new type of flu is determined by the first flu they had experienced. There are only 2 types of hemagglutinin protein and people are protected from the one their body meets first, but at risk from the other one. Researchers found out that there's a 75% protection rate against severe disease and 80% protection rate against death if person had been exposed to a virus with the same protein motif when they were children. Dr Worobey explains that the “Spanish Flu” pandemic was caused because first people were exposed to H1 virus and later they were exposed to a mismatched virus H3, which
