How vaccine works to stop virus

“The point is attenuation of virus. If it is possible to attenuate a virus, we can make a vaccine against the virus,” said Professor Seo Sang-hee at the Department of Veterinary Medicine in Chungnam National University. Attenuation is the most important part in the vaccine development process, according to Professor Seo. Attenuation means reducing the virulence of a pathogen, also known as a live virus. Attenuated vaccine does not inflict harm to a human body and stimulates the human immune system only, inducing immune responses against the virus. Once attacked by a virus, immune cells prepare to fight off the virus in the future, even when attacked by the virus in large scale, by enhancing the immune capability such as increasing the number of antibodies. Vaccines are developed based on this concept. Especially, vaccines are more effective to fend off the attack from a "rigid virus," which does not usually change its form.

A good example is the smallpox, which was once a deadly infectious disease accounting for 10% of the world’s death causes. Thanks to the smallpox vaccine development at the end of the 18th century, smallpox completely disappeared in 1977. At that time, World Health Organization (WHO) praised this as the greatest triumph in the history of vaccine development. It is not easy to develop a vaccine against a virus which changes like chameleon, such as influenza (flu). As the flu virus attacks a human body by changing its antigen so frequently, the WHO announces a new flu vaccine type every year. Flu virus’ speed to change its antigen is 10,000 times up to 100,000 times faster than that of the small pox. Several months before a flu season starts, the WHO predicts mutants of the flu virus which are expected to spread this season.

To save such efforts, scientists are now developing universal vaccines which can prevent any kind of flu virus, no matter how much the virus mutates. Earlier this year, the American research team started a clinical test on a universal vaccine, which is effective against all mutation of flu viruses for 20 years at least. For some viruses, it is hard to make an attenuated vaccine as they have a high fatality rate such as Ebola. To address those viruses, researchers are developing DNA vaccines by injecting antigens into a circular piece of bacterial DNA called a plasmid. As the DNA vaccine can maintain its original structure at high temperatures over 50 degrees in Celsius, it is convenient to use the vaccine in hot weather areas such as Africa where Ebola outbreak started. “So far, DNA vaccines’ immune responses has not been as effective as expected. Research is still in progress,” said Professor Seo.

Middle East Respiratory Syndrome (MERS) virus, which is rapidly spreading in Korea, was found in 2012. As it was recently found three years ago, vaccine has not been developed yet. Usually, it takes five to ten years to develop a vaccine. Some view that the low economic feasibility slows down development of MERS vaccines as there is very few infected by the deadly virus outside the Middle East region and Korea.

vamie@donga.com