266 Vaccines and Autism
last century, American, Japanese, Soviet, and British researchers examined the
potential for weaponizing smallpox but this was thwarted mainly due to
the efficacy of vaccines.
Individuals who received early versions of Jenner’s vaccine were immune to
smallpox. Even before Jenner introduced his vaccine, it was a common folk
remedy in many parts of Asia to scratch a dried scab from a smallpox ulcer on
to an individual’s skin. Most of these “scratched” individuals experienced a less
severe form of smallpox. These observations led to the practice of variolation
where people were inoculated artificially using pus from a pock or dried scab.
This practice, which likely originated in China during the 10th century, spread
at first to India and, by the 13th century, appeared in Egypt [14]. By the 17th
century, variolation was used widely, being introduced to England from the
Ottoman territories by Lady Mary Wortley Montagu in 1721. Interestingly,
Edward Jenner was also variolized prior to his discovery of vaccination in 1796.
After the advent of heat‐killed and formalin‐fixed bacterial vaccines, most
notably DPT, it was recognized that some sort of action needed to be taken to
ensure that vaccines were effective, safe, and free from other microbial agents.
This included the prevention of contamination and potential accidental
transfer of other diseases or infections. Traditionally, it has been difficult to
add antimicrobial agent(s) to live‐attenuated (weakened form of live virus) vac-
cines, since these agents can also harm the vaccine agents. Thus, preservatives
began to be added. Today, vaccines contain several components that aid in the
effectiveness and safety of the doses administered, in the form of adjuvants and
preservatives. Adjuvants are agents that make vaccines more powerful, enhance
their effects, and allow the immune systems to respond to the vaccine antigens
more robustly [15,16]. Preservatives are designed to prevent contamination of
unwanted microbes or viruses that can creep into a vaccine. Here, the addition
of thimerosal comes in. Thimerosal is an organomercury compound known for
its antiseptic and antifungal properties and has been used as an antibacterial
agent in pharmaceutical products, including vaccines and other injectable
biological products. Aside from thimerosal, some other chemicals being used
in vaccines can have known harmful side effects when introduced into the
body [16–22].
β‐Propiolactone is an organic compound commonly used since the 1950s as
a sterilizing agent for blood plasma, vaccines, bone and tissue grafts, surgical
instruments and enzymes. It is a colorless liquid with a slightly sweet odor and
is highly soluble in water. Controversially, it is considered to be a potential
carcinogenic agent, and has been shown to cause cancer when introduced to
mice, hamsters, guinea pigs, and rats [23].
Another additive, formalin, a 40% solution of formaldehyde in water, is also
used in vaccines to preserve the freshness and effectiveness of vaccines. As
mentioned earlier, some of the bacterial agents in DPT vaccine were treated
with formalin to render them inactive. When ingested, formalin can affect the