Nietzsche once wrote: "what does not kill me, makes me stronger". When it comes to natural poliovirus infection, this could indeed be the case.
Before the introduction of the polio vaccine in the late 1950s, most children naturally caught poliovirus. Around 70% of poliovirus infections were completely asymptomatic and resulted in no long-term problems; but around 0.5% of infections caused paralysis, and out of that 0.5%, around 1 in 30 cases were fatal (ref: 1).
Thus the introduction of the poliovirus vaccine undoubtedly saved numerous lives and prevented numerous disabilities. However, in spite of these considerable benefits, it is possible that poliovirus vaccine may also have a dark side, and may have inadvertently created some major health negatives.
It has been suggested that natural infection from wild poliovirus conferred some cross-immunity against the ill effects of other enteroviruses such as coxsackievirus B — a virus linked to ME/CFS and type 1 diabetes (T1D).
But poliovirus vaccine may not confer the same cross-immunity as natural poliovirus infection, and so individuals who were vaccinated and never caught poliovirus as a child may have reduced immunity to coxsackievirus B, and to related enteroviruses such as echovirus.
Decades later in life, when those vaccinated individuals catch coxsackievirus B or echovirus, their immune system may thus have more trouble fending off these infections, and this conceivably could increase the chances of developing ME/CFS or T1D from the infection.
So the introduction of the poliovirus vaccine in the late 1950s might potentially be the cause of the explosive 5- to 8-fold increase in the incidence of ME/CFS that appeared two decades later, in the 1980s. And the introduction of the poliovirus vaccine may have also caused the great increase in type 1 diabetes that appeared in the decades subsequent to introduction of the poliovirus vaccine.
Prior infection with poliovirus most likely does provide immunological cross-protection against coxsackievirus B, as this paper from Estonia talks about the differences between Estonian children immunized with the live attenuated polio vaccine, versus Finnish children immunized with the inactivated polio vaccine.
It was found that the Estonian children given the live vaccine have a stronger T-cell responses against coxsackievirus B4, which the authors suggest may explain why type 1 diabetes (linked to coxsackievirus B4) is 3 times lower in Estonia compared to its neighbor Finland.
So even with the two types of polio vaccine, the live virus vaccine seems to ramp up T-cell immune responses against other enteroviruses like coxsackievirus B more than the inactivated virus vaccine does. Presumably then, natural wild poliovirus infections in childhood will provide even stronger T-cell responses against other enteroviruses later in life.
Thus the loss of natural polio infections in the general population may have resulted in everyone becoming more susceptible to the ill effects of related enteroviruses.
It is a fascinating possibility that the introduction of the polio vaccine could have inadvertently led to a subsequent rise in the incidence of ME/CFS and T1D, because natural poliovirus infections in children were providing cross-immunity to ME/CFS- and T1D-triggering enteroviruses like coxsackievirus B.
To test this theory, it would be interesting to compare the prevalence of ME/CFS and T1D in individuals given the live attenuated polio vaccine (Sabin vaccine) as a child, versus the prevalence in those given the inactivated polio vaccine (Salk vaccine). That paper perhaps suggests that ME/CFS and T1D would be more prevalent among those give the inactivated polio vaccine.
The Sabin live polio vaccine is given orally on a sugar cube; the Salk inactivated vaccine is given by injection.
If it turned out to be true that the introduction of the polio vaccine has weakened our immunity to other enteroviruses, then this would only reinforce the need to develop a coxsackievirus B and echovirus vaccine with urgency, to be added to the vaccine schedule. By preventing natural poliovirus infection via the polio vaccination program, this may have allowed other enteroviruses to move in. So we need to developed vaccines for these other disease-causing enteroviruses too.
More info about the rationale for introducing a coxsackievirus B vaccine here: Coxsackievirus B vaccine appears feasible, and might conceivably abolish ME/CFS in future
Some keywords useful for Google searching on this topic: cross-immunity | cross-protection | cross-reactivity | cross-neutralization