February 16, 2019

Measles Again

Measles – a highly contagious viral disease with a characteristic rash – has been in the news of late. The most recent outbreak that made the news was in the Philippines, centering around Metro Manila, Luzon and Visayas. There have been at least 87 reported deaths and more than 5,600 cases reported this year, as of 2 days ago. This is part of a global phenomenon of measles, where the reported case count had virtually doubled between 2017 and 2018.

The World Health Organization (WHO) attributes this rise primarily to vaccine hesitancy, which is a “delay in acceptance or refusal of vaccines despite availability of vaccination services.” In the Philippines, officials have ascribed the drop in vaccination rates to the “Dengvaxia scandal” which occurred at the end of 2017. The Philippines had been one of the first countries to approve the dengue vaccine (Dengvaxia by Sanofi-Pasteur), and the Department of Health (DoH) had launched vaccination campaigns since April 2016. The subsequent finding that the vaccine may worsen dengue in those who had not previously been exposed to the disease led the DOH to suspend the campaigns in November 2017. But the damage in terms of trust in the immunization programme and the DoH had been done.

In the image below, obtained from the WHO vaccination scorecard, one can see that the vaccination coverage of the first measles vaccination dose (Mcv1) in Philippines hovered around 85% this decade. After 2017, this plunged to around 50%-60%.

In comparison, Singapore’s measles vaccination coverage (first dose) has consistently been 95%.

Vaccination coverage is particularly important for measles because it is one of the most contagious diseases known to us today. The reproductive number (R0) is estimated to be 12-18 on average (i.e. each case of measles would infect 12-18 other susceptible humans). It is a true airborne pathogen – the virus is viable as small particles in the air for up to 2 hours after a sneeze or cough, and an infected person is infectious up to 4 days before and after the rash appears. Thus the spread of measles is virtually impossible to prevent by physical means, and only widespread vaccination is likely to abort outbreaks before these have run their course. WHO has estimated that vaccination coverage of 95% is required for herd immunity and measles elimination.

Dealing with vaccine hesitancy – by no means straightforward as can be seen from the examples of many countries – is one of the most important challenges today given the rebound of childhood diseases such as measles. This will be a post for another day.

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Infectious diseases, Outbreak, Public Health, Singapore, Viral Infection


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