Taiwan's Measles Outbreak and Herd Immunity

Taiwan's Measles Outbreak and Herd Immunity
Photo Credit:AP/達志影像

What you need to know

Even those who have been vaccinated should still take basic precautions.

A regional outbreak of measles has afflicted Japan, Taiwan and now Hong Kong, but previous immunization campaigns mean that the disease is unlikely to become an epidemic.

The disease has infected at least 23 people in Taiwan so far, with thousands more potentially exposed. The outbreak appears to have begun on Japan's southern island of Okinawa and spread to Taiwan in late March 2018. Okinawan health authorities have confirmed at least 70 infections on the island.

Taiwan Center for Disease Control (CDC) Deputy Director-General Dr. Jen-Hsiang Chuang (莊人祥) told The News Lens in an email, "There is no community-wide outbreak of measles right now. Patients who contracted measles in the last month have possible exposure to the virus at Taoyuan International Airport and hospitals. People can protect themselves by getting vaccinated if they have no immunity against measles, and stay away from hospitals and other crowded places."

Chuang added that for the last 15 years, Taiwan has maintained two-dose measles-mumps-rubella (MMR) vaccine coverage of greater than 97 percent for children at school entry. Immunity induced by vaccination is known to last for at least 15 years.

Taiwan's MMR immunization rate is among the highest in the world. Compared to national surveys collected by the World Health Organization, only 28 countries worldwide have higher immunization rates than Taiwan.

MMR 2nd Dose Vaccination rates by country in 2016: (Hover or click for numbers, some data unavailable.)

Source: WHO, Taiwan CDC, U.S. CDC

The supply of measles vaccines has dropped sharply in the past week as people have rushed to be vaccinated, Taiwan's state-run CNA reported, adding that the remaining doses are under control of the CDC.

The spread of disease is often quantified through a basic reproduction number, or R0 (R-naught) – the average number of people that an infectious person will infect while they are contagious, assuming everyone in the population is equally susceptible.

Measles is commonly cited as having an R0 that is on the high side – between 12-18 (though estimates vary) – so it can potentially spread very quickly. However, as the vast majority of Taiwan is vaccinated or has contracted the disease in the past, measles has a high chance of fizzling out before it can become an epidemic – a concept known as "herd immunity."

Physician Liu Yi (劉奕) wrote in a letter published by The News Lens that most people in Taiwan have some level of immunity since the introduction of a full measles vaccine in the late 1970s, and that most cases of measles have been introduced to the country from overseas. Liu added that people who have contracted measles typically have lifelong immunity afterwards, but there have been cases of re-infection.

He said that those who believe that they have been infected should go to a hospital within 72 hours to get a vaccination, as measles has an incubation period lasting an average of 13 days.

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Liu Yi

Measles symptoms include a red, blotchy skin rash, cough, runny nose, inflamed eyes, sore throat and fever.

Measles can be deadly, especially to children under the age of five. The WHO estimates that 89,780 people died of measles in 2016, but deaths had fallen 84 percent since 2000. Among vulnerable groups such as refugees, up to 30 percent of those who contract the disease die.

Measles Infections by Country January-April 2018

Source: WHO, Taiwan CDC, U.S. CDC. (Some numbers only updated to March 30)

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