To diseases and viruses, because God protects his children? Of course not. However plenty of religious people are immune to reason and are immune to disbelief. This is the defining basis as to why religion persists in modern times, it’s because at the end of the day they still want to believe in God.
In all of the debates as to whether God exists there is a huge collection of sensible arguments to provide reasons not to believe. I’m not going to drill into the arguments here, but suffice to say there is a rational and reasonable case against God, the details of which can be found elsewhere. The point that I will make, and the point which it ultimately boils down to, is this: The religious think it is okay to believe something, no matter the arguments, if it cannot be disproved outright. This is the fallback of all religious debates, regardless of how good the points were against God’s existence. If you cannot disprove his existence to them there and then; it is still okay to say he still exists. The religious are refusing to accept the arguments against God, not because they are inherently flawed or because the reasoning isn’t clear, but because they do not want to acknowledge the validity of the arguments.
Refusing to suspend disbelief because it cannot be proven is a flawed line of reasoning. The burden of proof lies with those who are trying to prove God does exist, not to those who try and prove he does not. To see this point more clearly we can summon Russell’s teapot. I make the claim that there is a teapot, orbiting the Sun, yet it is too small to be seen by Earth’s most powerful telescopes. Clearly I have made this up (or in fact Bertrand Russell did), but how can you disprove my conjecture? I have been careful enough to make sure you cannot disprove my teapot. This is an identical case to God: refusing to acknowledge the arguments against him because they cannot prove his non-existence. This is flawed. You cannot rely on something’s inability to be disproved; you can only logically rely on something’s ability to be proved.
In every other instance in humanity, people believe something if it can be proven. If the case for God was made in an impartial court of law, it would fail. The faithful shield themselves by refusing to acknowledge that it should be them giving the case for God. They shield themselves against disbelief by refusing to take on board arguments against God. It comes down to a very deep seated reason inside the hearts of the faithful; they want it to be real.
The religious want it be to real and they enjoy it being real. They shut themselves off from reason, because they want their God to be existent. This is a stalemate. This is their immunity. There is nothing further to be said to this religious mind. If from the start they are going to be biased and narrow minded, then there is no way of removing their God-tinted glasses. There is no medium through which you can reason with somebody who refuses to listen to your arguments.
Thus there will always be a core, as with people who refuse to accept the Earth is 4.5 billion years old, as with people who think Noah’s flood really happened, there will always be those who are willing to believe even in the face of a mountain of counter evidence. It is only from within, that these people could challenge their own belief in God and truly engage with the arguments against his existence. They have to be willing to suspend their vested interest. Sadly to say there will be some who never challenge their faith and these people are a lost cause.