Among vaccine-preventable diseases, measles is one of the major causes of death in children. Although the disease incidence has reduced by about 90% since vaccinations were introduced, regular measles epidemics are reported in developing countries, while as recurrent episodic outbreaks are observed in the developed world.
According to a new study published in The Lancet Infectious Diseases, the role played by demographics in the spread of measles was demonstrated by Bocconi University and Bruno Kessler Foundation. Data from around 9 countries (Australia, Ethiopia, Kenya, Ireland, Italy, South Korea, Singapore, the UK, and the US) were analyzed and it was concluded that future vaccination strategies in high-fertility countries should emphasize on increasing childhood immunization rates, while immunization campaigns targeting adolescents and young adults are required in low fertility countries.
A transmission model calibrated on historical serological data, revealed that the susceptible proportion of the population (i.e. unprotected against the infection) was estimated. The susceptibility rates were found to be 3% in the UK, >12.5% in Ethiopia, 74% in South Korea, 66% in Italy and 53% in the US with considerable immunity gaps in individuals aged 30-40 years.
Alessia Melegaro from Bocconi University said that, "Every effort to increase the vaccination coverage rate among children is praiseworthy." However in some developed countries, lack of attention among adolescents and adults leads to serious threat to the goal of eliminating measles.
Stefano Merler from Bruno Kessler Foundation, reports that "Measles incidence could increase, in the next decades, in Italy, Australia and Singapore and Ethiopia is at high risk of future large epidemics." As the individuals are infected in their later life when the disease is more severe. The median age at infection for 2015 was estimated to be 5-10 years in the UK, Ireland, and Ethiopia; 10-15 years in the USA, Australia, Singapore, and Kenya; and older than 20 years in Italy and South Korea.
The findings suggest that the introduction of the measles vaccination minimized the disease burden in terms of disability-adjusted life-years (DALYs). Each vaccine dose prevents 2-3 weeks of DALYs in the developed countries and about 20 weeks in Kenya and Ethiopia.
“Vaccination has undoubtedly achieved incredible results in terms of public health.” Prof. Melegaro stated "our analysis showed that routine first dose vaccine administration has been responsible for more than 90% of the overall number of vaccine-immunized individuals in most countries. In Ethiopia and Kenya, catch-up and follow-up campaigns substantially mitigated the effect of suboptimum routine vaccine coverage, generating 25-45% of the immunized fraction of the population. Tailoring immunization campaigns to achieve measles eradication goals is essential and currently, for some countries, this means considering also the role of unprotected adolescents and young adults."