Page 20 - Science Focus (issue20)

does not normally propagate for more than several
Vaccine Development
疫苗研究的發展
By Paolo Miguel Magallanes Mallorca
Vaccines! Everyone is talking about it lately. We may In 1796, English physician Dr. Edward Jenner proved
see them as the way out of this dreadful pandemic this observation by inoculating an eight-year-old
that made 2020 a mess. The good news is that some boy with cowpox. The boy only developed fever
COVID-19 vaccines are approved and now being and minor symptoms. After his sickness subsided, the
distributed to billions of people on this planet. With the boy was exposed to smallpox samples but did not
vaccines making headlines, have you ever wondered developed the disease. After publishing the results
where and how do vaccines originate? of the experiments, Dr. Jenner called this procedure
“vaccination” (derived from the latin word vacca,
meaning cow) and it became more popular than
"Vaccination” Before Dr. Edward Jenner variolation [2]. Countries in Europe began to enforce
The earliest sign of “vaccination” was documented vaccination and saw significant decline in mortality
in ancient China and India, in the 10th Century [1]. rate [1].
The idea was to collect smallpox samples from blisters
of a sick individual and inoculating minute amounts Dr. Louis Pasteur: The Father of Immunology
on healthy individuals. This practice wasn’t called
vaccination but “variolation” (after the smallpox virus While Dr. Louis Pasteur is well known for
Variola major). It spread across some countries in Asia pasteurization, a method to reduce the load of
and Africa, eventually reaching Britain and other microbial pathogens in food by heat, little attention
parts of Europe in 1721 [2]. While it was quite effective is given to his other contribution: live-attenuated
at protecting people from smallpox and controlling vaccines. Inspired by Dr. Jenner’s works, he suggested
outbreaks, inoculated individuals still have a small risk of that there can be vaccines for other diseases as well. former generation, which uses whole pathogens,
developing smallpox or other diseases transmitted by
this procedure [2]. In 1877, positing that vaccines could be found
for all virulent diseases, Dr. Louis Pasteur attempted
to work on chicken cholera [3], a bacterial disease
Dr. Edward Jenner: The that was devastating chicken populations. One time
Pioneer of Vaccines before going on a holiday, he instructed his assistant
to inoculate chickens with fresh bacterial samples.
I n the 170 0 s, some The assistant forgot and upon returning, he inoculated
milkmaids were reported the chickens with samples that had been sitting in the
t o h a v e i m m u n i t y laboratory for a long time. The inoculated chickens
a ga i n s t sm a l l p o x . survived, and remained healthy upon exposure to fresh
This was likely due to samples afterwards. It was later discovered that the old
prior infection with samples were probably weakened due to prolonged
cowpox, a disease exposure to oxygen, but could still induce immunity. This
similar to but milder is the first example of a live-attenuated vaccine.
than smal lpox.
Dr. Pasteur’s accidental discovery of the chicken
cholera vaccine inspired him to work on other diseases.
In 1885, he worked on rabies, a fatal neurological
d i s e a s e i n d o g s a n d
humans. It was discovered
that growing rabies virus
in other hosts like rabbits
where the microbe
generations (scientifically termed serial passage), could
weaken their virulence to the original host [3]. Through
this method, weakened viral strains were collected
and tested on dogs. After they successfully induced
immunity in dogs, Dr. Pasteur tested the same strains on
a boy who was bitten by a rabid dog. The boy did not
show rabies symptoms.
Dr. Pasteur’s work shows that weakened pathogens
may induce immunity against the disease they cause.
This treatment was also named vaccination, which was Types of vaccine summarized:
originally referring to only smallpox, to honor Dr. Jenner’s 1. First-generation vaccine = whole pathogen (live-
previous work [3]. attenuated, inactivated)
2. Second-generation vaccine = pathogen pieces
Modern Vaccine Development (subunit, recombinant)
3. Third-generation vaccine = DNA based; mRNA
Breakthroughs in microbiology and molecular based
biology in the 20th century drove the development of
more vaccines. Not only there were vaccines available
for more diseases, but there were new methods of The Future of Vaccine Research
creating vaccines and new types of vaccines as well.
Looking back at how vaccines developed,
It was discovered that pathogens carefully killed
by heat or chemical treatment can induce immunity, we have come a long way in protecting people
from deadly diseases. In 1980, the W.H.O. declared
creating inactivated vaccines. The first successful smallpox’s eradication, the complete removal of a
inactivated vaccines were created in the 1890s against disease from the human population. More diseases
typhoid fever and plague. This technique was expanded like malaria and polio may face the same fate in
to viruses as well, and by 1936, a vaccine for influenza the future. We have even managed to create a
was invented [4]. vaccine against COVID-19 within a short period
of time. As more vaccines become available and
Inactivated vaccines and live-attenuated vaccines as more research is done, the containment or the
are referred to as first-generation vaccines. The second- eradication of certain deadly diseases is now a
generation vaccines are subunit vaccines. Unlike the possibility, thanks to scientists like Dr. Jenner and Dr.
Pasteur.
subunit vaccines use components of the pathogen
that can be targeted by the immune system to develop
immunological memory [4]. With the recent advances
in genetic engineering, one variant of subunit vaccines
uses recombinant DNA technology to mass-produce
these components in other organisms or cells, such as
yeast, animal cells and insect cells [4].
Then is the relatively new, third generation of
vaccines. Instead of administering patients with whole
pathogens or their components, genetic materials
coding for those components in the form of DNA or
mRNA are used. These genetic materials will be read
by cells as instructions to produce viral components
for the immune system to target. Due to the COVID-19
pandemic, both DNA and mRNA vaccines are
receiving a lot of attention lately, which are the first
of their kind to be approved for emergency use in
humans. The development of DNA and mRNA vaccines
was spurred unprecedentedly by the race to develop
vaccines against COVID-19. Besides their application in
the pandemic, research is being done for the potential
use of such nucleic-acid based vaccines against
cancer and HIV [5].
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