Over the past 14 months, South Africa has experienced its highest rise in diphtheria cases in 30 years, with doctors attributing this to waning immunity and low vaccine levels, and suggesting that adult booster shots should be considered in the future.
Seven people have already died from the highly contagious vaccine-preventable bacterial infection, with the outbreak mostly concentrated in the Western Cape, according to the National Institute for Communicable Diseases (NICD).
News24 reports that cases have also been reported in Gauteng, Mpumalanga and KwaZulu-Natal, but at significantly lower levels.
In its latest report released last Thursday, the NICD said 69 cases were recorded between January 2024 and 9 March this year.
It is the first time a diphtheria outbreak has lasted so long and with so many cases, it said.
Gauteng and Mpumalanga have also experienced a death each, the latest being in Mpumalanga.
“It is concerning,” said the NICD’s Professor Anne von Gottberg, “because this is a vaccine-preventable disease – and the vaccine prevents people from getting sick, and from dying from this disease.”
The NICD issued a countrywide alert in January, asking clinicians “to have a high index of suspicion for respiratory diphtheria in patients presenting with a sore throat, low-grade fever, malaise and an adherent membrane (sticky, greyish membrane at the back of the throat), and/or a bull neck”.
It has also begun publishing situational weekly reports since late February, and con confirmed that for every case, a public health response has been initiated, which includes isolation, tracing and testing of contacts, medication administration, and enhanced vaccination campaigns.
Cape infections
In the Cape, most of the cases were in the Cape Town metro area, with one on the West Coast.
The NICD said that since November there has been a marked increase of cases in the province, with five clusters reported. Many were in young adults aged between 20 and 30, with only a few in the 30-34-year-old age group.
Dr Hassan Mahomed of the Western Cape Health Department said not all positive cases are people who get seriously sick.
“There are people who get really, really ill, and then there are people who are a little bit sick, they get treatment and they recover. And there have also been a big number of people who don’t have any symptoms.
“This is why contact tracing and testing is important, so that those asymptomatic individuals don’t unknowingly spread the bacteria.”
The 67 cases the NICD recorded include 36 that are asymptomatic carriers of the bacteria.
South Africa has previously only experienced sporadic cases of diphtheria, and never with numbers as high as this. The largest was in 2015, with four deaths from 15 cases over four months in KwaZulu-Natal. Before that, between 2000 and 2015, only seven confirmed cases were recorded.
Between 2015 and May 2023, 44 cases were recorded in sporadic bursts. The largest recent outbreak was in 2023, with the biggest cluster of nine cases in Pollsmoor prison where one person died.
High age, waning immunity
What is unusual about this outbreak is the age of people who have diphtheria, which hovers around 28.
“That’s a little old,” Von Gottberg said, “and tells us that there may be an element of waning immunity because they didn’t get their older children boosters, and they may be more vulnerable.”
Six diphtheria vaccines are administered to children: at six, 10, and 14 weeks, and then boosters at 18 months, and again at six and 12 years.
Though vaccine coverage for the first three doses is generally high, coverage for the booster shots drops sharply, resulting in immunity that wanes as a person ages.
WHO data show that for 2023, diphtheria vaccine coverage for the first dose is 80%, while the third dose (14 weeks) is 78%. For the fourth dose (18 months), vaccine coverage is 69%. Data for six and 12-year vaccines for 2023 are not yet available.
In 2022, the vaccine coverage for the last two boosters was at 17% and 15%, respectively. Significantly, vaccine coverage for these booster shots in 2021 was 8% for the fifth and 1% for the sixth doses.
In Cape Town, Mahomed said that young adults are getting infected “because not enough of them get those six years and 12 year shots”.
Vaccine coverage among six-year-olds for diphtheria fell from 42% in 2021/2022 to 39%, and then 37% in 2023/2024. It was even more stark among 12-year-olds, with 17% in 2023/2024 and 18% in the preceding two years.
“For this vaccine, your level of immunity drops as you get into your early adult years, so you're not as well protected as when you are young.
“I think we should perhaps consider, in the future, having boosters for adults as well.”
See more from MedicalBrief archives:
Diphtheria prison outbreak contained
WHO, Unicef flag worst decline in childhood immunisations in 30 years
UK health agency warning over antibiotic-resistant diphtheria strain