The immune system varies in performance throughout a person’s life. During infancy and early childhood, when the immune system is immature, people are in danger of becoming infected with a persistent microbe such as cytomegalovirus, chlamydia, Lyme disease organism, or a herpes-like virus.

In fact, by age 3, 100 percent of small children test positive for another type of latent herpes virus called HHV-6. That virus also may play a role in Alzheimer’s disease.

Among children ages 6 to 16, those who test positive for HSV-1 infection have been shown to have lower reading and spatial reasoning scores. Both HSV-1 and cytomegalovirus infections in middle-age adults (ages 20 to 59) are associated with impaired learning and recall.

As we reach older age, the immune system also ages and we once again become susceptible not only to new infections, but also to reactivation of existing latent infections — sleeping viruses, bacteria, and spirochetes.

Such latent infections can have harmful effects on cognition throughout life. The more often a person has a reactivation of these sleeping viruses, the greater his or her risk not just of developing Alzheimer’s dementia, but also social problems related to thinking, educational attainment, and social mobility.

These viral reactivations are directly dependent on the health of the immune system. What we are now seeing is that more and more people are suffering from immune impairment caused by factors such as:

• Poor diet

• Diabetes

• Chronic stress

• Exposure to industrial chemicals

• Exposure to pesticides, herbicides, and fungicides

• Excessive vaccinations

People are especially vulnerable to these factors during early life and old age. Of these factors, I think the worst are the vaccines, because the majority of vaccines are known to shift the immune system to what is called a Th2 mode, which suppresses immunity. That children receive 40-plus vaccines before they enter school may be a major cause of chronic infections.

Once a persistent virus establishes itself, it too can suppress immunity. The measles virus, for example, is a major suppressor of immunity, and the measles vaccine uses a live virus.

Studies have shown that in a high percentage of people, the measles virus persists in the brain for a lifetime.