EXPLAINER/Things to know about measles: Symptoms, transmission, vaccination

Taipei, Jan. 11 (CNA) A total of 19 measles cases linked to a hospital cluster in central Taiwan have been reported as of Friday, sparking concern about the highly infectious disease and its potential spread.

CNA has compiled answers to some frequently asked questions about measles, including its symptoms, transmission, vaccination, and steps to take if an individual has been in contact with a measles case.

Symptoms of measles

Measles is a highly contagious respiratory disease caused by the measles virus. On average, an individual will develop a rash - one of the typical symptoms of the disease -- 14 days after exposure to the virus, with an incubation period ranging from seven to 18 days, according to the Centers for Disease Control (CDC).

The disease is contagious even before the rash develops, said Ingrid Wu (吳明穎), an attending physician at Chang Gung Memorial Hospital in Linkou.

Wu said early signs of measles are worth noting, including cough, rhinitis, and conjunctivitis.

If any of these occur along with a fever and rash, it may not be a common cold, Wu said.

The appearance of "Koplik spots" -- irregular red spots with white centers that form on the mucous membranes on both sides of the oral cavity -- is a key indicator of measles before the rash develops.

How is measles transmitted and how contagious is it?

Measles can spread easily when an infected person breathes, coughs, or sneezes, leading to severe illness, complications, and even death, according to the World Health Organization.

Huang Chien-hsien (黃建賢), an attending physician at Shin Kong Wu Ho Su Memorial Hospital, said that measles is transmissible from four days before and after the development of a rash.

One infected individual can spread the virus to 12 to 18 people, Huang added.

CDC Director-General Chuang Jen-hsiang (莊人祥) said medical research has shown that receiving two doses of the measles vaccine can lower viral loads in an infected individual's body, thereby reducing their ability to transmit the virus compared to unvaccinated individuals.

Vaccine eligibility and availability

The measles, mumps, and rubella (MMR) vaccine is available through Taiwan's publicly funded vaccination program.

The vaccine is provided free of charge to Taiwanese children, with one dose administered to children at 12 months old and another dose given to children aged 5 to 6 years, before entering primary school, the CDC said.

Foreign children residing in Taiwan can also receive the MMR vaccine free of charge, provided they or their parents meet certain criteria, such as being enrolled in Taiwan's National Health Insurance (NHI) program or holding a valid resident certificate, a CDC guideline read.

While the MMR vaccine in Taiwan is also available for self-paid vaccination, Lee Ping-ing (李秉穎), convenor of Taiwan's Advisory Committee on Immunization Practices (ACIP), said that those with known allergies to vaccines, pregnant women, and individuals with severe immune deficiencies should not be vaccinated for the MMR vaccine.

Who should consider a booster dose of MMR vaccine?

Taiwan has implemented a universal vaccination program for infants and young children since 1978, and thus most individuals born in or after 1981 have not contracted measles, with their MMR vaccine-induced immunity may wane over time, according to the CDC.

Certain high-risk groups are recommended to get self-paid MMR boosters, including healthcare workers born in or after 1981 who lack proof of measles immunity within the past five years and whose last MMR dose was administered over 15 years ago, the CDC said.

People born after 1981 who are traveling to measles-endemic countries such as Vietnam, India, and Cambodia are also advised to get booster doses, the CDC added.

For individuals born before 1981, natural immunity is common among such individuals due to past infections, and nearly 100 percent of them retain immunity, according to Lee.

What to do if placed under self-health management?

Contacts of measles cases do not need to undergo isolation but are required to follow self-health management for 18 days from the last contact with an infected individual, Chuang said.

During the self-health management period, individuals should check their temperature twice daily. If no symptoms or discomfort arise, they may continue with their normal daily activities but should wear a mask and avoid crowded public spaces, Chuang added.

If a contact develops symptoms suggestive of measles during the period, they should immediately self-isolate and inform health authorities. A medical evaluation will be arranged with a designated route to minimize contact with others at medical institutions, and masks must be worn at all times during the visit, according to the CDC.