Adolescence is an important time to review vaccinations. Protection from some childhood vaccines can weaken over time, and teenagers may encounter new infections as they become more socially active. Vaccination can help protect them against infections and their long-term complications, including certain cancers caused by human papillomavirus (HPV), meningococcal disease, influenza, whooping cough, hepatitis B, measles, mumps, rubella and chickenpox.

The vaccines recommended for each teenager depend on their age, medical history, previous vaccinations and possible exposure to infection.

In Singapore, the National Childhood Immunisation Schedule (NCIS) and National Adult Immunisation Schedule (NAIS) guide vaccination recommendations. School-based vaccination programmes and additional recommendations for people with particular medical conditions or exposure risks also play a role. The United States, United Kingdom and Australia recommend many of the same vaccines, but their schedules, eligibility criteria and funding arrangements differ.

1. Why are vaccinations important during adolescence?

Vaccination during adolescence helps maintain protection from childhood, prevent certain cancers and reduce the risk of infections. It is also an opportunity to catch up on vaccinations that may have been missed earlier.

1.1 Maintaining protection as immunity weakens

Protection against infections such as whooping cough, tetanus and diphtheria can weaken over time. Booster doses help maintain protection.

Teenagers who missed some childhood vaccinations may also need catch-up doses to protect them against measles, mumps, rubella, polio, hepatitis B and chickenpox.

1.2 Preventing cancer and long-term complications

HPV vaccination is particularly important because it helps prevent infections that can cause several types of cancer. These include cervical, anal, vulvar, vaginal, penile and some cancers of the mouth and throat. Depending on the vaccine, it can also prevent genital warts.

HPV vaccination works best before a person is exposed to the virus. Studies have found substantial reductions in cervical precancerous changes and cervical cancer following the introduction of HPV vaccination programmes.

Hepatitis B vaccination is also important. It helps prevent long-term infection that can lead to liver scarring (cirrhosis) and liver cancer.

1.3 Reducing the spread of infections

Teenagers spend time in schools, universities, sports activities and social settings where infections can spread. Some infections, including meningococcal disease, influenza, whooping cough and COVID-19, can cause serious illness. The risk varies depending on the infection and the individual's circumstances.

1.4 Protecting the wider community

When more people are vaccinated, fewer people may become ill. For some infections, vaccination can also reduce their spread. This helps protect people who are more vulnerable to severe illness, including infants and people with weakened immune systems.

1.5 Catching up on missed vaccinations

Some teenagers may have incomplete vaccination records because they moved to Singapore, missed school vaccination sessions or had interruptions in their healthcare. Others may be unsure which vaccines they have received.

Reviewing vaccination records during routine adolescent health visits helps identify missing doses and determine whether catch-up vaccinations are needed.

2. Which teenagers may need additional vaccination?

Some teenagers have a higher risk of infection or are more likely to develop complications. Their vaccination needs should be assessed individually.

Teenagers in crowded or residential settings

Teenagers living in boarding schools, university accommodation or other shared settings may have more opportunities to encounter certain infections, including meningococcal disease and respiratory infections.

The MenACWY and MenB vaccines may be recommended when indicated by local guidance, an outbreak or travel requirements.

Teenagers with chronic medical conditions or weakened immune systems

Conditions such as asthma, chronic lung or heart disease, diabetes, kidney disease and certain neurological conditions can increase the risk of complications from influenza, COVID-19 and some other infections.

Some conditions, including having no functioning spleen or having certain problems affecting the immune system, can also increase the risk of serious infections.

The level of risk depends on the condition and its severity. Teenagers with weakened immune systems may need additional vaccine doses or different vaccine formulations. Some live vaccines may not be suitable for them, so medical advice is important before vaccination.

Teenagers with incomplete vaccination records

Teenagers who have moved from overseas, recently arrived in Singapore or missed school vaccination programmes may not be fully protected against measles, mumps, rubella, chickenpox, hepatitis B, polio and other vaccine-preventable infections.

Their vaccination records should be reviewed, and catch-up vaccinations arranged where needed.

Teenagers who travel or have other exposure risks

Travel to areas experiencing outbreaks, pilgrimage, certain work-related exposures and contact with animals may increase the risk of particular infections.

Depending on the destination and circumstances, teenagers may need vaccines against meningococcal disease, hepatitis A, Japanese encephalitis, rabies or yellow fever.

Teenagers who may be exposed to HPV or hepatitis B

HPV vaccination is most effective before exposure to the virus and is recommended for eligible adolescents regardless of whether they are sexually active.

Catch-up hepatitis B vaccination is important for teenagers who missed vaccination during infancy. Vaccination may also be relevant for people with certain blood or sexual exposure risks.

3. Benefits and possible side effects of vaccines

Vaccination is very effective in preventing serious infections as well as some types of cancers, and also ameliorates the complications associated with these infections, which include damage to the brain, lungs and other organ systems.

Most vaccine side effects are mild and go away on their own. These may include a sore arm, tiredness, headache or a mild fever. Such reactions are usually part of the body's response to vaccination.

Serious reactions are rare and should be assessed by a healthcare professional. However, a health problem that occurs after vaccination is not necessarily caused by the vaccine. Doctors consider when the symptoms started, the person's medical history and other available evidence when assessing whether a vaccine may have contributed to the problem.

The following section describes four vaccines that may be relevant to adolescent healthcare.

4. Summary of adolescent vaccinations: