Why fully vaccinated children can still get diphtheria — Paediatricians

Children who have received all recommended primary doses of diphtheria-containing vaccines can still develop the infection, paediatricians have warned, as protection may wane over time or fail to produce adequate immunity in some children.

The experts, however, stressed that vaccination remains the strongest protection against diphtheria, as it substantially reduces the risk of severe disease, complications and death, even when breakthrough infection occurs.

They explained that completing the primary vaccination series does not guarantee lifelong protection, making timely booster doses and sustained immunity essential for preventing breakthrough infections and controlling outbreaks.

Diphtheria is a highly contagious bacterial infection caused by Corynebacterium diphtheriae, which usually affects the nose and throat and can produce a toxin that damages the heart, nerves and other organs. In severe cases, the infection can cause breathing difficulties, heart inflammation, paralysis and death.

In an exclusive interview with PUNCH HealthWise, Head of Paediatrics at the Federal Teaching Hospital, Katsina, and Team Lead, Diphtheria Case Management, Dr Abdurrazzaq Alege, explained that completing the primary vaccination doses does not guarantee that a child’s immunity against diphtheria will remain strong indefinitely.

“The immunity wanes over time. Despite having three doses, after a year, the immunity wanes. So that is the essence of the booster,” he explained.

Alege noted that Nigeria’s routine immunisation programme provides the primary diphtheria-containing vaccine at six, 10 and 14 weeks, but stressed that protection could decline without subsequent booster doses.

He said the vaccination status of a child should therefore be assessed by considering the number of doses received and whether the child had received the appropriate additional doses needed to maintain protection.

“Basically, we’ll say that the child who is fully vaccinated can still develop diphtheria,” he stated.

According to the paediatrician, another concern was that some vaccinated children might not develop sufficient antibody levels to provide adequate protection, even when they had received the recommended primary doses.

“Sometimes it may not be adequate to stimulate immunisation or production of antitoxin in the system,” he explained.

Alege also identified vaccine-handling problems as a possible contributor, explaining that a break in the required cold-chain conditions could affect vaccine potency before administration.

“If there is any defect or breakage in this, it can affect the potency of the vaccine that is going to be administered,” he cautioned.

He stressed that high vaccination coverage remained essential because widespread immunity reduces transmission and protects people who have not been fully immunised.

“The essence of herd immunity is to protect other children who are not completely immunised or not immunised. It confers protection on them,” he said.

Alege urged parents to check their children’s immunisation records and ensure that they received all recommended doses, particularly during an outbreak.

He also advised parents to seek prompt medical attention if a child developed symptoms suggestive of diphtheria, including fever, sore throat, painful swallowing, cough, runny nose or a membrane in the throat.

“Any symptom that is suggestive should make the child and the parents worry and not take any chances,” he advised.

• Potential new TB vaccines could save millions of lives – Expert
• Stigma hinders cancer patients, survivors from seeking support – Doctors 
• Sleeping with earbuds may trigger hearing loss, say ENT specialists

The World Health Organisation states that diphtheria vaccines are highly effective but recommends a three-dose primary series followed by three booster doses in childhood and adolescence to produce and sustain long-term immunity. WHO also notes that booster doses strengthen and extend protection when immunity from the primary series weakens over time.

The United States Centers for Disease Control and Prevention similarly notes that diphtheria vaccination protects strongly against the effects of the diphtheria toxin but does not necessarily prevent infection or carriage of Corynebacterium diphtheriae, meaning vaccinated people can still carry or become infected with the bacterium.

Nigerian research has also provided evidence that vaccination does not always translate into adequate antibody protection.

A 2026 study of 257 Nigerian children aged six months to 59 months found that 54, representing 21 per cent, had no detectable immunity against diphtheria, while only 10 children, or 3.89 per cent, had antibody levels classified as providing long-term protection. The researchers concluded that significant proportions of Nigerian children had inadequate immunity despite receiving the three primary doses of diphtheria-containing vaccine.

Further evidence came from an outbreak investigation conducted in Edo State between May and September 2024. Of 19 suspected cases managed at the University of Benin Teaching Hospital, five were laboratory-confirmed. Among 10 children whose blood samples were tested for diphtheria antibodies, seven, or 70 per cent, had inadequate protective levels.

An earlier WHO report on Nigeria’s outbreak also recorded breakthrough infections, with 1,074, or 22.8 per cent, of confirmed cases reported as fully vaccinated, while 299, or 6.3 per cent, were partially vaccinated. The figures show that confirmed cases can occur among vaccinated people, but do not mean that 22.8 per cent of fully vaccinated children will develop diphtheria.

A June 2025 PUNCH report also documented infections among fully vaccinated people during an outbreak in Edo State. The report quoted the Edo State Commissioner for Health, Dr Cyril Oshiomhole, as saying that people who had been fully vaccinated were among those infected during the state’s outbreak.

Speaking exclusively with PUNCH HealthWise, Consultant Paediatrician at the Olabisi Onabanjo University Teaching Hospital, Sagamu, Ogun State, Dr Femi Akodu, explained that the diphtheria vaccine primarily protects against the toxin produced by the bacterium rather than completely preventing the bacterium from entering or colonising the body.

“The key concept is that diphtheria vaccination primarily protects against the diphtheria toxin, rather than preventing colonisation or infection by the bacterium itself,” he explained.

Akodu said a vaccinated child could therefore still become infected, particularly where immunity had declined, although vaccination substantially reduces the risk of severe toxin-mediated disease.

“Vaccines are not 100 per cent effective. A small proportion may not develop adequate immunity despite appropriate vaccination,” he stated.

He stressed that the occurrence of infection in a vaccinated child should not be interpreted as meaning that vaccination is ineffective.

“Receiving all recommended doses of diphtheria-containing vaccine does not provide 100 per cent protection against acquiring Corynebacterium diphtheriae. Its most important benefit is protection against diphtheria toxin and therefore clinical disease, severe disease, and complications such as myocarditis and neuropathy,” he said.

Akodu advised parents to maintain their children’s immunisation records and ensure that all age-appropriate diphtheria-containing vaccines and recommended boosters were received.

He also urged parents not to dismiss symptoms simply because a child had been fully vaccinated, particularly during an outbreak.

“Contact a healthcare professional urgently if a child develops a sore throat and fever during an outbreak, especially if the child has had close contact with a suspected or confirmed case,” he advised.

The paediatrician further warned parents against waiting for the characteristic membrane to develop before seeking care.

“Do not wait for the membrane to appear. Diphtheria can initially look like an ordinary throat infection, and early treatment is important because complications become more likely as toxin-mediated disease progresses,” he cautioned.