Vaccines have never been 100% effective. The big effect is “herd immunity.” If an infected person would have spread the disease to 10 other people, but all are vaccinated using a vaccine with a 5% failure rate, then the victim will inflict, on average, only half a person. In other words, on averaage, 16 people will infect 8, who will then infect 4, who will then infect 2, who will infect 1, who has 1 50% shot of infecting another 1, and so on. On average, those 16 will spread the disease to only 16 others before the outbreak dies out. Even though vaccine failure may be devastating to the infected individual, even an imperfect vaccine can provide tremendous population to the population at large.
4 Likes
