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How vaccines work

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A mother gets her child vaccinated at the Health center in Baseco compound in Tondo, Manila on Feb. 11. — PHILIPPINE STAR/KRIZ JOHN ROSALES

Smallpox was a serious and highly contagious infectious disease caused by the variola virus. People infected with smallpox developed a fever and a distinctive, progressive skin rash. It was a devastating disease. About 3 out of every 10 people with smallpox died, according to the US Centers for Disease Control and Prevention (CDC). Many survivors are permanently scarred over large areas of their body, especially their faces; some are left blind. In the late 18th century, the English physician Edward Jenner first demonstrated smallpox immunization. About 180 years later, thanks to global vaccination efforts, smallpox was eradicated and no case of naturally occurring smallpox has occurred since 1977.

The story of how immunization led to the eradication of smallpox, a public health accomplishment that has been called one of humanity’s greatest triumphs, was shared by Dr. Anna Lisa Ong-Lim during the “Forum on Vaccination and its Public Health Impact” held last month at the Philippine Medical Association (PMA) Auditorium in Quezon City. Dr. Ong-Lim, the current President of the Pediatric Infectious Disease Society of the Philippines (PIDSP), spoke on “The Science and Journey of Vaccines.”

Viruses and bacteria cause many infectious diseases. Viral illnesses include the common cold, chickenpox, and measles, while bacterial illnesses include typhoid fever and tuberculosis. “Our immune system is the body’s defense against these infectious microorganisms,” Dr. Ong-Lim explained. “Through a series of steps called the immune response, the immune system recognizes the disease-causing invaders and reacts by sending ‘soldiers’ in the form of special immune cells and proteins to eliminate the infection.”

According to Dr. Ong-Lim, a vaccine is a biological preparation containing the inactivated or weakened microorganism. “When introduced into the body, a vaccine ‘trains’ the immune system to defend itself quickly when a particular virus or bacterium invades through natural means.” Vaccines stimulate the body’s immune system to recognize infectious microorganisms as foreign, destroy them, and “remember” them, so that the immune system can more easily recognize and destroy any of these microorganisms that it later encounters. Like any other medicine, vaccines can have side effects. However, most vaccine reactions are usually minor and temporary, such as a sore arm or mild fever. These usually resolve spontaneously. In the rare event a serious side effect is reported, it is immediately investigated.

“Vaccines prevent sickness and death caused by vaccine-preventable diseases. Immunization protects the individual and the community,” stressed Dr. Ong-Lim. When the majority of a given population is immunized, the disease-causing organism or pathogen can no longer spread within the community. This phenomenon is known as “herd immunity” or “community immunity,” which gives protection to people who for whatever reason are not getting vaccinated.

In the wake of the measles outbreak in the country, Dr. Ong-Lim called on all stakeholders in both the government and private sector to unite in restoring public trust and confidence in vaccination in order to prevent further sickness and deaths.

With the Department of Health as main partner, the PMA, Philippine Foundation for Vaccination (PFV), Philippine Alliance of Patient Organizations (PAPO) and the Pharmaceutical and Healthcare Association of the Philippines (PHAP) are working together to restore vaccination trust and confidence in the country.


Teodoro B. Padilla is executive director of the Pharmaceutical and Healthcare Association of the Philippines (PHAP). Medicine Cabinet is a weekly PHAP column that aims to promote awareness on public health and health care-related issues.

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