Philippines explainer: Polio back after 19 years of being declared 'polio-free'

Manila: Nineteen (19) years after it was declared polio-free, the Philippines is once again facing the crippling — at times fatal — disease.

Health Secretary Francisco Duque III announced that one confirmed polio case signaled an “epidemic” in a once polio-free country.

He said a 3-year-old girl from Lanao del Sur was diagnosed with a vaccine-derived polio virus Type 2. The Department of Health (DOH) is awaiting confirmation of a suspected case of acute flaccid paralysis (AFP).

On Friday, September 20, officials confirmed a second case of polio. This time, the victim is a 5-year-old from Laguna province south of Manila after samples were found positive for the polio virus.

In the Lanao case, the onset of illness was detected on June 26 and was confirmed by the National Institute of Infectious Diseases on September 14, 2019.

Officials added the polio virus has also been detected in sewage in Manila and in waterways in the southern Davao region, prompting plans for an immunization drive starting next month that is likely to include tens of thousands of children under age 5.

In 2000, the World Health Organisation (WHO) declared the Philippines polio-free.

What is the health authorities' response?

Duque identified poor coverage, environmental sanitation and hygiene, and suboptimal AFP surveillance as the factors that brought about the relatively low immunization rate for polio.

“The DOH … is preparing a rapid response to the polio outbreak. This includes a series of synchronized oral polio vaccinations to protect every child under the age of 5 years in areas at risk beginning in October,” Dr Duque said.

The average national polio vaccination coverage is 66 to 68 percent, according to the health secretary. The goal is to bring the average to 95 percent.

Consequently, the DOH will rollout a vaccine specifically targeting the Type 2 strain, in addition to a supplemental polio immunization program.

Health Undersecretary Myrna Cabotaje said they were awaiting the delivery in the first week of October of the "monovalent vaccine" that would come from the WHO headquarters in Geneva, where it has been stockpiled in the event of an outbreak.

Rabindra Abeyasinghe, country representative of the World Health Organization (WHO), clarified that the vaccines previously used by the DOH were not meant for the Type 2 polio virus strain that was found in the two new cases.

Cabotaje said that apart from supplemental immunization programs, the DOH will also intensify its surveillance mechanisms since it was possible that it missed acute flaccid paralysis (AFP) cases.

The DOH said that a decreasing AFP rate means “we may not be able to find true cases of polio and may experience resurgence of polio cases.”

What are the priority areas for anti-polio vaccinations?

Lanao del Sur, Cavite and Davao — the areas where the Type 2 strain was recorded — will be prioritised in the vaccine distribution, according to Cabotaje.

In the case of Manila, the Type 1 VDPV strain was detected in two tests conducted on the city’s sewage. The current bivalent oral polio vaccine (OPV) used by the DOH targets the Type 1 and Type 3 polio strains.

Cabotaje said that even if a child below 5 years old had already completed his polio vaccination, he or she would still be given the vaccine “for added protection.”

“That is what the other countries are doing until there are no more recorded cases,” she said. “What’s important [with the distribution of the] monovalent vaccine is to cover everyone. We don’t want anyone to be left behind in an area, so that the virus would not be able to mutate.”

How can ordinary citizens fight polio? 

The polio virus can be transmitted through fecal-oral route contamination.

The DOH advises the public to practice good hygiene by washing hands, using toilets, drinking safe water and cooking food thoroughly.

Duque also identified poor coverage, poor environmental sanitation and hygiene, and suboptimal AFP surveillance as the factors that brought about the relatively low immunization rate for polio.

Cabotaje said that apart from supplemental immunization programs, the DOH will also intensify its surveillance mechanisms since it was possible that it missed acute flaccid paralysis (AFP) cases. Based on latest DOH data, AFP surveillance declined significantly between 2017 and 2018. Ideally, countries without poliovirus transmission should have an AFP reporting rate of 1 per 100,000 children below 15 years old.In the first quarter of last year though, the number of regions which were able to meet this dropped to 3 from 13 in 2017. This resulted in the country’s AFP reporting rate dropping from 1.48 per 100,000 in 2017 to a dismal 0.82 per 100,000 the following year. This was way below the 1.38 reporting rate recorded in 2011, when the Philippines was also deemed at high risk of polio reemerging. The DOH said that a decreasing AFP rate means “we may not be able to find true cases of polio and may experience resurgence of polio cases.”

What is the Dengvaxia controversy?

The low turnout of the national immunization drive — against polio and MRM (measles, mumps, and rubella) — in recent years was due to other factors, explained Duque.

The DOH chief cited one caregiver who did not want a child to be vaccinated. The health secretary specifically cited the Dengvaxia controversy as one of the factors that contributed to low public confidence in vaccines.

Some doctors, including DOH officials, had blamed Chief Public Attorney Persida Acosta for the declining public confidence in the government’s immunisation program.

Following the death of 145 people, mostly children, who were inoculated with Dengvaxia, Acosta declared the vaccine as the main culprit. 

After the PAO filed criminal cases against health officials and drug companies in early 2018, she has also been blamed for the surge in measles cases in six out of the country’s 17 regions earlier this year.

Acosta, a lawyer, said the health agency should take responsibility for the two outbreaks because of the vaccines it used. She blamed the agency's poor information drive for its immunisation program.

She said the two children — one 3-year-old and one 5-year-old — who were found stricken with polio should have been inoculated when they were 2-6 months old, at least three years ago.

What is OPV?

Oral poliovirus vaccines (OPV) are the predominant vaccine used in the fight to eradicate polio.

There are different types of oral poliovirus vaccine, which may contain one, a combination of two, or all three different serotypes of attenuated vaccine. Each has their own advantages and disadvantages over the others.

Monovalent vs bivalent vs trivalent OPV: What's the difference?

A monovalent vaccine is designed to immunize against a single antigen or single microorganism.

Since April 2016, governments around the world have switched from the trivalent to bivalent OPV because, according to the Global Polio Eradication Initiative (GPEI), continuously using the trivalent OPV increases the risk of circulating the Type 2 strain.

What are vaccine-derived polio viruses (VDPVs)?

Vaccine-derived polioviruses (VDPVs) are rare strains of poliovirus that have genetically mutated from the strain contained in the oral polio vaccine.

In 1999, the wild or naturally occurring Type 2 strain was declared eradicated. Up until 2015, 90 percent of VDPV cases were linked to the Type 2 strain.

What is the WHO's advice to tourists to the Philippines?

Because of the VDPV outbreak, the WHO has recommended that travelers to the polio-affected areas be fully vaccinated against polio.

WHO also noted that tourists staying for more than four weeks “should receive an additional dose of OPV or inactivated polio vaccine within 4 weeks to 12 months of travel.”