The repeated resurfacing of diphtheria amongst adolescents and older age groups in many districts in the State is an evidence of the epidemiological shift in disease burden that the State has been undergoing for the past decade.
These sporadic cases would come down and older children, adolescents and women of reproductive age would be afforded better protection against diphtheria when the Centre implements the World Health Organisation recommendation to replace Tetanus Toxoid (TT) vaccine with Tetanus-adult Diphtheria (Td) vaccine, public health experts said.
One of the worst diphtheria outbreaks in the State had been in 2016, when over 500 cases had been reported across districts. The disease had surfaced in 2017 and 2018 too, with more cases amongst adolescents and older persons.
2 cases in Malappuram
Last week, two cases of diphtheria were reported in two 15-year-olds in Malappuram district, while an isolated case had been confirmed in a 21-year-old from Thiruvananthapuram on Friday.
According to WHO, after the introduction of vaccine in a population where diphtheria is endemic, the epidemiologic patterns undergo changes in two stages. At first, the disease burden shifts to children of school-going age and in the second stage, it moves to adolescents and young adults.
Even when the primary vaccination coverage against diphtheria is high, immunity is known to wane in late childhood or adolescence.
Checking outbreak
But the potential of an outbreak among a large population of susceptible adults can be checked if the primary immunisation coverage is over 90% and if sufficient booster doses of the vaccine are administered to adolescents and older population.
“The National Technical Advisory Group on Immunisation had in 2016 itself recommended that while diphtheria surveillance systems should be strengthened, replacing TT vaccine with Td vaccine would be an ideal public health intervention to bring down the susceptibility to diphtheria amongst the older populations. Kerala too had been pushing for this after the huge diphtheria outbreak it had in Malappuram and other districts in 2016. The Union Health Ministry had announced last year that TT booster doses at 10 and 16 years of age, two doses of TT or single booster dose of TT given to pregnant women, will be replaced by Td by the end of the year. We are now waiting for its implementation,” a senior Health official said.
Vaccination intensified
Routine immunisation activities were intensified across the State after the huge diphtheria outbreaks it had in 2016, when 533 cases were identified in 11 districts. These large number of cases were despite the fact that Kerala has always had a high coverage of DTP (diphtheria, pertussis, tetanus) vaccine over 85%.
About 92% occurred in three districts of north Kerala — Malappuram, Kozhikode, and Kannur. Cases were also reported from Wayanad, Palakkad, Thrissur, Kasaragod, Alappuzha, Ernakulam, and Thiruvananthapuram.
Almost 79% of the cases occurred in the above 10 years age group. Just 7% of the cases were children under 5 years while another 7% were in the age group of more than 45 years, affirming the fact that booster doses were necessary to protect adolescents and adults from diphtheria.
Measles too
The same trend is currently being witnessed in the case of measles also, with a high proportion of cases in those above 15 years of age.
