The 5-in-1 or 6-in-1 injection is the most complex vaccine your baby receives — covering up to six separate diseases in a single shot. It is the backbone of the infant immunisation schedule, starting at just 2 months of age. Understanding what it protects against helps explain why it cannot be delayed.
Diphtheria is caused by a bacterial toxin that creates a thick grey membrane across the airway. Children can asphyxiate within hours. The toxin also attacks the heart and nerves. In the pre-vaccine era, diphtheria killed thousands of children in Singapore. Compulsory vaccination has reduced it to near-zero — but imported cases remain a threat.
The tetanus toxin causes relentless, uncontrollable muscle spasms. The jaw muscles seize shut (hence "lockjaw"), followed by arching of the back and spasms of every major muscle group. Without intensive care, tetanus kills by respiratory failure. The bacterium is found in soil and enters through wound contamination — vaccination is the only reliable protection.
Whooping cough earns its name. Infants experience paroxysmal coughing fits so severe they cannot breathe — followed by the desperate "whoop" as they finally inhale. In babies under 3 months, there may not even be a whoop: instead, they simply stop breathing (apnoea). Severe pertussis in young infants can cause brain damage from prolonged oxygen deprivation.
The most vulnerable group is infants under 2 months — too young to have received even their first dose.
Polio destroys the motor neurons in the spinal cord, causing permanent flaccid paralysis — most commonly of the legs, sometimes the respiratory muscles (requiring iron lungs in pre-vaccine era). Singapore's last case was in 1989. That it has not returned is entirely due to sustained vaccination.
Hib was the leading cause of bacterial meningitis in children under 5 before vaccination. It causes not just meningitis but also epiglottitis — a rapidly fatal swelling of the airway. The Hib vaccine has virtually eliminated these diseases in vaccinated populations.
Why the surge? Three compounding factors:
The most dangerous cases are in infants under 2 months — too young to have received any DTaP doses. Protecting these babies requires everyone around them to be vaccinated (cocooning strategy).
In Singapore, the standard 6-in-1 vaccine is Infanrix Hexa (GSK), covering diphtheria, tetanus, pertussis, polio, Hib, and hepatitis B in a single injection.
Diphtheria vaccination is compulsory under the Infectious Diseases Act. Singapore's near-elimination of diphtheria is a direct result of this compulsory programme — one of the clearest public health success stories of the past 50 years.
A red, firm, swollen area at the injection site (thigh or arm) is normal for 24–48 hours — this is a local inflammatory response, not infection. Fever in the first 24–48 hours is also common and normal. Paracetamol (at age-appropriate dosing) can be given if your child is uncomfortable. The swelling resolves on its own. Do not apply ice or rub the injection site. If fever exceeds 39°C or persists beyond 48 hours, consult your doctor.
💡 For new parents: If you have an unvaccinated newborn, make sure the adults closest to them — parents, grandparents, caregivers — are up to date on their Tdap booster. This "cocooning" approach is recommended by MOH Singapore and is the best way to protect babies too young to be vaccinated themselves.
References
Communicable Diseases Agency (CDA) Singapore. Weekly Infectious Diseases Bulletin, 2024.
Ministry of Health Singapore. National Childhood Immunisation Schedule (NCIS).
WHO. Pertussis vaccines: WHO position paper. Weekly Epidemiological Record. 2015.
CDC. Epidemiology and Prevention of Vaccine-Preventable Diseases (Pink Book). Pertussis chapter. 2021.