The Centers for Disease Control (CDC) has recommended that all travelers to the Philippines be fully vaccinated against polio, as the country declared an outbreak of the disease on Sept. 19.

The risk of the disease spreading further throughout the country is high due to a limited vaccination coverage rate.

The Philippines has confirmed three cases to date. All three were caused either by vaccine-derived poliovirus type 2 (VDPV2) or the lack of prior vaccination, the CDC said.

It said the WHO on Oct. 25 assessed the risk of further spread within the Philippines to be high due to a population immunity of about 66 percent.

The WHO also stated that the risk of international spread is low.

CDC Deputy Director-General Philip Lo (羅一鈞) said that the oral polio vaccine contains a weakened vaccine-virus that activates an immune response in the body.

On rare occasions, if a population’s vaccination coverage rate is low, the vaccine-virus can be transmitted to unvaccinated people.

The national childhood immunization program in Taiwan for polio has a four-dose schedule of 5-in-1 vaccines targeting children at the age of 2, 4, 6 and 18 months, and a dose of 4-in-1 vaccines between five years old and before entering elementary school.

Lo said the vaccination coverage rate in Taiwan is about 99 percent, and three doses provides at least 99 percent immunity.

The CDC urged parents to not bring children under six months, or those who have not received the third dose of the vaccination, to visit the Philippines.

Polio viruses are spread predominantly through the fecal-oral route, when the stool of an infected person is consumed through contaminated water or food, Lo said.

The virus could be found in throat secretions as early as 36 hours after exposure and in stool, 72 hours after exposure, Lo added.

The CDC said the WHO recommends visitors of all ages who are intending to stay in the Philippines for four weeks or more to receive a single dose of inactivated poliovirus vaccine.

This dose should be taken no later than four weeks before their scheduled date of travel, if they have not received a polio vaccination in the last 12 months, the centers said.

It said more than 90 percent of people infected with polio suffer no symptoms or mild symptoms, including fever, tiredness, weakness, malaise, headache, nausea and vomiting.

About 1 to 2 percent of people may develop nonparalytic aseptic meningitis, and less than 1 percent might suffer paralysis, the CDC added.