Vaccine

Definition of Vaccines

Vaccination is a simple, safe, and effective way of protecting you against harmful diseases, before you come into contact with them. It uses your body’s natural defenses to build resistance to specific infections and makes your immune system stronger.

Vaccines train your immune system to create antibodies, just as it does when it’s exposed to a disease. However, because vaccines contain only killed or weakened forms of germs like viruses or bacteria, they do not cause the disease or put you at risk of its complications.

How Do Vaccines Work?

Vaccines enhance the immune system’s capacity to fight infectious agents by exposing the body, in a safe and controlled manner, to antigens associated with specific pathogens. This process stimulates the development of immune memory without causing the full disease. Consequently, when the body is later exposed to the actual virus or bacterium, the immune system can recognize the pathogen rapidly and generate a faster, stronger, and more effective immune response.

Figure 1. Overview of the major technology platforms used for COVID-19 vaccine development, the SARS-CoV-2 variants of concern and their respective spike protein mutations, and the factors that may influence the effectiveness of available vaccines.

Are Vaccines Safe?

Vaccines are considered highly safe and are subject to extensive evaluation before approval for public use. Their safety is assessed through rigorous preclinical studies and clinical trials to ensure that they meet established standards of quality, efficacy, and safety. Regulatory authorities only authorize vaccines for registration and distribution after these requirements have been satisfactorily fulfilled. In contrast, failure to vaccinate may place children at substantially greater risk of contracting serious vaccine-preventable diseases and experiencing related complications.

Why Should Children Be Vaccinated?

Vaccination is one of the most effective public health interventions for reducing childhood illness and death. It protects children against serious infectious diseases and is especially important for infants and young children, whose immune systems are still immature and more vulnerable to severe complications. Immunization also helps prevent the re-emergence and spread of highly contagious vaccine-preventable diseases, such as measles, diphtheria, and poliomyelitis, including in settings where these diseases had previously been eliminated or well controlled. Therefore, routine childhood vaccination is essential not only for individual protection but also for maintaining broader community health.

What Diseases Can Vaccines Prevent?

Vaccines protect both children and adults against a wide range of infectious diseases that are associated with substantial morbidity and mortality. Routine immunization is widely recommended by governments and healthcare professionals because it reduces the risk of severe illness, long-term complications, disability, and death. The major vaccine-preventable diseases include the following:

Tuberculosis (TB)
Tuberculosis is a bacterial infection that most commonly affects the lungs, although it may also involve other organs, including the brain. It can occur at any age, but the risk is higher among older adults and immunocompromised individuals. In severe cases, pulmonary tuberculosis may lead to serious complications or death. Once infection is established, treatment is often prolonged and may not always achieve complete recovery.

Hepatitis B
Hepatitis B is a viral infection transmitted through blood, sexual contact, and from mother to child. Infection acquired early in life is often asymptomatic for many years, but chronic infection may later progress to liver cirrhosis and hepatocellular carcinoma.

Poliomyelitis (Polio)
Polio is an acute viral disease transmitted primarily through the fecal–oral route. Poliovirus may cause irreversible paralysis in approximately 1 out of every 200 infected individuals. Among those who develop paralysis, 5% to 10% die as a result of respiratory muscle involvement. There is no curative treatment once paralysis has occurred; management is limited to supportive care and symptom control.

Diphtheria
Diphtheria is a serious bacterial infection caused by Corynebacterium diphtheriae. It primarily affects the mucous membranes of the nose and throat and may lead to difficulty breathing or swallowing. Severe infection can also damage the heart, kidneys, and nervous system.

Tetanus
Tetanus is caused by Clostridium tetani and is characterized by muscle rigidity and painful spasms. In children, it may present with stiffness of the jaw and neck, difficulty opening the mouth, swallowing impairment, and respiratory distress. Despite treatment, tetanus is still associated with a high fatality rate.

Pertussis (Whooping Cough)
Pertussis, caused by Bordetella pertussis, is a highly contagious bacterial infection characterized by severe coughing episodes that may persist for weeks. Complications include breathing difficulties, pneumonia, and, in severe cases, death.

Diseases Caused by Haemophilus influenzae Type b (Hib)
Hib is a bacterium that can cause pneumonia, meningitis, and other serious invasive infections, particularly in children younger than five years of age.

Pneumococcal Diseases
Pneumococcal infections, caused by Streptococcus pneumoniae, include severe illnesses such as pneumonia and meningitis, as well as more common conditions such as sinusitis and otitis media. These infections remain an important cause of morbidity and mortality worldwide, especially among children under two years of age.

Rotavirus Infection
Rotavirus is a major cause of severe diarrhea and vomiting in young children. It can result in dehydration, electrolyte imbalance, and shock. Without prompt treatment, particularly rapid fluid replacement, the infection may become fatal.

Measles
Measles is a highly contagious viral disease characterized by fever, rhinorrhea, Koplik spots, and a generalized skin rash. Severe complications include blindness, encephalitis, and death.

Mumps
Mumps is a viral infection that may cause fever, headache, malaise, and inflammation of the salivary glands. Potential complications include meningitis, orchitis, and deafness.

Rubella
Rubella is usually a mild infection in children and adults. However, infection during pregnancy may result in miscarriage, fetal death, neonatal death, or congenital abnormalities.

Human Papillomavirus (HPV) Infection
HPV infection is often asymptomatic, but certain high-risk types are strongly associated with cervical cancer, which is one of the most common cancers among women worldwide. Nearly all cases of cervical cancer are linked to genital HPV infection. HPV may also cause genital warts in both males and females and can contribute to cancers in other anatomical sites.

References
National Assembly of the Socialist Republic of Viet Nam. Law on Pharmacy No. 105/2016/QH13, issued 6 April 2016, effective 1 January 2017.
UNICEF Viet Nam. Frequently Asked Questions About Vaccines.
World Health Organization. (2025, November 28). Measles deaths down 88% since 2000, but cases surge.

Trần Khánh, M.Sc.
Kim Ngọc Sơn, M.Sc.