Most Nigerian parents have never seen a case of diphtheria. That was the point — it is one of the diseases the childhood vaccine was supposed to have ended. Which is exactly why the last few years have been such a shock.

Nigeria has recorded more than 10,000 confirmed diphtheria cases in 2026 alone. Going further back, the country’s health agency counted 1,319 deaths between 2022 and early 2025, from more than 42,600 suspected cases across 37 states. The 2023 wave was officially Nigeria’s worst diphtheria outbreak in a decade — 13,387 confirmed cases and 598 deaths among them.

There is one detail in those figures that changes how you should read this entire article: only about one in four of the confirmed cases had been fully vaccinated.

This is not a mysterious new plague. It is an old, well-understood, entirely preventable disease returning through a gap we left open.

What diphtheria actually is

Diphtheria is caused by a bacterium — Corynebacterium diphtheriae — that spreads from person to person through coughing, sneezing and close contact. What makes it dangerous is not the bacterium sitting in the throat. It is the toxin the bacterium releases.

That toxin does two things, and both can kill:

  1. It builds a membrane in the throat. Dead tissue and debris form a thick, greyish coating over the tonsils and back of the throat. Unlike ordinary tonsillitis, this membrane sticks firmly, and it can grow until it blocks the airway.
  2. It travels. Absorbed into the bloodstream, the toxin can damage the heart muscle and the nerves, days after the sore throat first appeared — which is why a child can seem to be improving and then deteriorate.

The warning signs — know these

Diphtheria often starts looking like an ordinary sore throat. Watch for the combination:

  • A sore throat that is getting worse rather than better
  • A thick grey or white membrane at the back of the throat or over the tonsils — the single most characteristic sign
  • Swelling of the neck — sometimes so marked it is described as a “bull neck”
  • Difficulty breathing or swallowing, noisy breathing, or a barking cough
  • Fever, usually low-grade, with unusual weakness

Any grey membrane in the throat, or any child struggling to breathe, is an emergency. Do not wait it out. Do not treat it at home with leftover antibiotics or a chemist’s guess. Go to a hospital.

Why it is a hospital emergency — not a chemist problem

Diphtheria needs two things that only a health facility can give: antibiotics to kill the bacteria, and diphtheria antitoxin to neutralise the toxin already circulating. Antibiotics alone do not undo toxin that has already been absorbed, and the antitoxin works best when given early — before the toxin reaches the heart and nerves. Every hour of “let’s see if it improves” is a real loss.

A child whose airway is closing may also need urgent support to keep breathing. None of this can happen in a shop.

The uncomfortable truth: this is a vaccination-gap disease

Here is where the numbers become impossible to ignore.

  • In the 2023 wave, only 3,376 of 13,387 confirmed cases — 25.2% — had been fully vaccinated against diphtheria. The overwhelming majority were unvaccinated or only partly vaccinated.
  • 9,048 of those confirmed cases — 67.6% — were children aged 1 to 14.
  • Confirmed cases have clustered overwhelmingly in the north: Kano, Yobe, Bauchi, Katsina, Borno, Plateau, Jigawa and Kaduna together account for 99.7% of confirmed infections — with Kano State alone making up roughly three quarters of them. NCDC’s 2026 updates name Kano, Borno and Bauchi as the states carrying the outbreak now.

Diphtheria protection comes from a toxoid vaccine. In Nigeria it is delivered inside the pentavalent vaccine, which protects against five diseases at once — diphtheria, pertussis (whooping cough), tetanus, hepatitis B and Hib — and it is given as three injections, at 6 weeks, 10 weeks and 14 weeks of age. It is free under the national immunisation programme. (Pentavalent replaced the older standalone DPT injection from 2012, so an older card may show “DPT” instead.)

The vaccine has not stopped working. It has simply not reached enough children — or reached them once or twice and never been completed. A partly vaccinated child is not a protected child.

What to do this week

  1. Find your child’s immunisation card and read it. Look for pentavalent (an older card may say DPT). You are looking for all three doses — at 6, 10 and 14 weeks. One or two is not the full course.
  2. If doses were missed, you can still catch up. Take the card to the nearest primary healthcare centre and ask them to complete the schedule. Missing a dose does not mean starting over, and it does not mean it is too late.
  3. If there is no card, go anyway and ask to be assessed — do not assume.
  4. Know the signs above — grey membrane, swollen neck, breathing difficulty — and act on them the same day.
  5. If someone in your household is diagnosed, tell the clinic that others live in the house. Close contacts may need treatment and vaccination themselves.

The bigger picture

Diphtheria sits alongside the other lessons this site keeps returning to: that fever and sore throat in Nigeria are too often guessed at rather than diagnosed. We have written about why “malaria and typhoid” is so often the wrong answer, about Lassa fever hiding behind malaria’s symptoms, and about checking that the medicine you buy is genuine. Diphtheria adds one more: some illnesses are not meant to be treated at all — they are meant to be prevented, years earlier, with a free injection and a completed card.

There is a small piece of good news in the data. Nigeria’s diphtheria case-fatality rate has fallen compared with the same period last year, as surveillance and treatment have improved. The dying is becoming less common. The catching is not — and that part is still in our hands.

The pocket check

Grey membrane in the throat, a swollen neck, or trouble breathing → hospital today. And before any of that: read your child’s immunisation card, and complete what’s missing. Diphtheria is a disease we already know how to defeat. It only comes back when we stop finishing the job.

This article is for information only and is not a diagnosis or a treatment plan. Diphtheria is a medical emergency — if you suspect it, go to a hospital immediately.

Sources: Nigeria Centre for Disease Control (NCDC) diphtheria situation reports and 2026 outbreak statements; World Health Organization diphtheria fact sheet; WHO African Region Disease Outbreak News; Gavi, “In northern Nigeria, a deadly diphtheria outbreak delivers a grim warning”; Nigerian press reporting of NCDC cumulative figures (2022–2025).