Scientists have once again disproved the theory that vaccines cause autism, and insist that parents should continue to protect their kids with preventive shots.
Nowadays, autism is affects around 1 in 70 children in the United States, and the number of cases has been climbing in recent decades, leaving scientists struggling to find an explanation.
Some people had theorized that the neuro-developmental disorder may be caused by childhood vaccines, especially by those containing thimerosal, a mercury-based preservative usually encountered in multi-dose vials.
However, at the time, researchers concluded that except for minor side effects such as redness and swelling the substance causes no side effects.
Nevertheless, in July 1999 health organizations agreed to reduce or eliminate the preservative from preventive shots, and as of 2001 thimerosal has been removed from childhood vaccines. Despite this ban, autism rates are still increasing, which further suggests that the preservative was never the cause of such cases.
It has been speculated that in fact the prevalence of autism may seem higher now because the condition can be more easily identified by medical practitioners. Behavioral signs such as repetitive patterns, communication problems and impaired social interaction have been accepted as reliable ways of diagnosing this disorder.
This recent research was led Bharathi S. Gadad of the University of Texas Southwestern Medical Center, and one of the major groups that funded it was the National Autism Association.
The study was published on September 28 in the journal PNAS and analyzed 79 male infant rhesus macaques, for around 18 months starting from birth. These primates were selected to be part of the experiment because their brain development and body functions are similar to those of human babies.
12 of the animals were administered vaccines containing thimerosal, based on guidelines followed by doctors in the 1990s, when children had the highest exposure to this preservative.
Another group of 12 macaques received the measles, mumps and rubella (MMR) vaccine, which doesn’t include thimerosal. This is still the vaccine that is currently recommended today for the prevention of these childhood diseases.
A control group was administered placebo injections containing saline. Other groups of primates received more frequent doses of each type of injection, to account for the species’ faster rate of growth.
Researchers then analyzed the behavior of macaques at the age of 12 to 18 months, which corresponds to a human age of 4, when the presence of autism becomes more discernible.
It was established that vaccines containing thimerosal caused no disruption in brain function and no behavioral modifications linked to the onset of autism. Similarly, the MMR shot resulted in no changes in behavior or brain activity.
None of the macaques had repetitive patterns, or other symptoms like rocking, head-banging, huddling and self-clasping. Also, while autistic children have modifications in the cerebellum, hippocampus and the amygdala, no such changes were identified in the macaques, no matter how high the vaccine dose had been.
Based on these findings, researchers urge parents to continue protecting their children through preventive shots, as recommended by the American Academy of Pediatrics and the Centers for Disease Control and Prevention. Current vaccines are actually very safe and can help children ward off diseases at a time when they’re at their most vulnerable.
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