Thus far only 53.8% of Americans have been fully vaccinated for COVID, a deadly virus. 
The percentages vary around the world but overall the figure is about 42%. Poverty aside (mainly in third world countries) what accounts for this? At root, philosopher Immanuel Kant, an ardent defender of religion, claimed that reality was unknowable.
Let’s begin with well-known facts. Infections are based on two, interacting factors: the degree of exposure (intensity and duration) and one’s immune defenses. Infection results when exposure overwhelms one’s defenses. Exposure is controlled by keeping a distance from other people and masking, and bodily immunity is provided by vaccination. 
So why don’t some people do it?
- Religion: some people think God will protect them as if a ghost in the sky will override the laws of biology.
- Misinformation: there are a lot of irrational and dishonest posts out there if one looks for them, e.g., there are good substitutes for the vaccine, there are cures based on some obscure plant or pill, the vaccine will cause COVID or make people infertile, etc. But it is easy to check out these claims (eg., thru reputable websites) and refute them if one uses even a bit of effort.
- The refusal to look for accurate information–vaccine agnosticism as a deliberate policy–how can you really know?
- Conformity: Lots of people, including my friends and relatives, oppose the vaccine. The collective must be right. Who am I to oppose them?
- Fear (or false hope) based on any of the above. But people have free will and can choose to act despite their fears based on their rational judgment so they do not have to give in to the fear.
The fundamental cause then is the refusal to think. So much for the claim that people possess an instinct for self-preservation.
Let me add that all employers should have the absolute right to say: you cannot work here if you are not vaccinated and/or you must wear a mask at work. They also should have the right to decide which customers they will trade with. Such policies should be publicly announced.
I am not going to get into here how much power the government should have on this matter. Ayn Rand said that people who test positive should be isolated. The details would have to be worked out by legal scholars. 
 As of September 11, 2021, at least 208,704,230 people or 64% of the population have received at least one dose. Overall, 177,899,458 people or 54% of the population have been fully vaccinated. Source: CDC.
 Immunity can also occur via natural infection, which in immune-compromised and older age groups may lead to serious illness, hospitalization and death. — Editor
 See Onkar Ghate’s paper, A Pro-Freedom Approach to Infectious Disease, for some recommendations. — Editor
Editor’s Note: Edwin Locke’s article applies to some adults who do not get vaccinated (and not necessarily to children). There are cases where the individual has used reason and come to the conclusion that they should not be vaccinated (perhaps, a pre-existing condition where vaccination is contraindicated, or they have recovered from a COVID infection, and testing shows they have sufficient antibodies). In such cases, the individual has made a proper exploration and is not simply using such reasons as an excuse to justify their emotions or religiously-held beliefs against vaccination, etc. Similarly, a decision should be an individual one and not a decision based purely on a government mandate. Vaccine(s) are safe for most people, based on the information available, however, there are still unknowns, and the decision to vaccinate, should be based on the long-term, self-interest of the individual.