Herd immunity— If a lot of people are protected from a pathogen then the people who arent protected, are still protected. The higher the percentage of ‘protected’ people, the better herd immunity works.
While we generally think of herd immunity as it relates to the very young/old, immunocompromised, those who cannot get vaccinated for medical reasons, this concept matters to all of us. Like I said in my talk at FreeOK last year— your immune response to a vaccine is random, so there are some of you reading this article whos parents dutifully got them their MMR vaccines as babies, and yet you do *not* have a protective immune response for measles. You wont know you happened to react this way until some anti-vax parents (read: terrible parents) expose you to their measles infected offspring.
While the ideal levels of vaccine coverage for herd immunity are usually >80%, a paper was just published in Pediatrics that illustrates just how dramatic the effects of herd immunity can be, even if coverage rates are low:
These researchers followed a group of girls/young women who did not get the HPV vaccine, and another group that got at least one dose of the HPV vaccine (now, this is important, the HPV vaccine requires three doses for it to work best, so the percentages in this paper are low-balling what we would expect if girls were getting all three doses).
The young women who got at least one dose of the vaccine saw a reduction in vaccine-HPV infection of ~70%. Again, not bad considering some participants only had one of the three recommended doses.
Heres the cool part: The young women who had not gotten the HPV vaccine saw a reduction in vaccine-HPV by ~50%.
The protected women prevented transmission of HPV to males (this study was restricted to mainly heterosexual contact), which prevented those males from infecting the unprotected females, to the tune of a 50% reduction in vaccine-HPV lesions.
How high would both of those numbers shoot up (70% and 50%) if the protected group was getting all three doses?
How high would that 50% jump if more women were getting all three HPV shots?
Its heartening to know that even if anti-vax or radical religious parents wont protect their children from deadly diseases (or unfortunately, the parents who want to, but cant protect their kids because of the expense of the HPV vaccine series), science will protect those kids anyway.