A Department of Health (DOH) official assured the public that the country is still “polio-free,” even as she warns that the country is at high risk of poliovirus transmission because of the “very low” vaccine coverage and poor sanitary practices and conditions.
The country was declared “polio-free” by the World Health Organization in October 2000. The DOH has not recorded any case of wild poliovirus in 26 years since 1993.
However, the discovery of a vaccine-derived poliovirus in a sewage in Manila last July by the Research Institute for Tropical Medicine has given rise to concerns about the re-emergence of polio in the country.
Health Assistant Secretary Dr. Maria Rosario Vergeire, however, clarified that although two samples tested positive for vaccine-derived poliovirus, there has been no reported case of anyone in the country being sick of poliomyelitis.
No “herd immunity”
Polio could lead to paralysis and even death. There is no cure for it but it could be prevented by complete vaccination.
Polioviruses spread through the oral-fecal route. A person is infected through food, water, or objects contaminated with feces from an infected person. Anyone who has not been fully immunized—or did not get the three doses of Oral Polio Vaccine (OPV)—is at risk of getting polio.
Vergeire explained that vaccine-derived poliovirus, like that found in the Manila sewage, is different from the wild poliovirus. But both can cause polio.
OPV contains the weakened poliovirus, which triggers the immune response against polio without causing the disease.
On rare occasions, if the population is not adequately vaccinated with OPV, the weakened virus can change into vaccine-derived poliovirus (VDPV), a rare form that has regained its ability to cause polio.
This would pose no risk to the population if at least 95 percent of the population is fully immunized, or what is called “herd immunity.”
In the Philippines, however, only 66 percent of the population one- year-old and below were fully immunized against polio in 2018. That leaves 34 percent of them at risk of acquiring the disease.
Declining rate of immunization
Three doses of OPV are required to be fully protected from the poliovirus. In addition, the DOH has also included one dose of Inactivated Polio Vaccine (IPV) as part of its routine immunization schedule and Expanded Immunization Program, which aims to protect children from vaccine-preventable diseases, including tuberculosis, DPT (diphtheria, tetanus, pertussis), Hepatitis B, Influenza Type B, and Measles.
OPV provides protection in the mouth and intestines. This is important as polioviruses infect the mouth and multiply in the intestines.
Meanwhile, IPV, which is injected, provides protection in the blood. It further strengthens the protection given by OPV and increases overall protection from polio.
DOH data, however, show that coverage for the third dose of OPV over the last 10 years since 2008 has remained below the 95% target needed to attain herd immunity or ensure protection of the population against polio.
And OPV coverage has been further declining by an average of 1 percent each year since then, hitting the lowest in 2018 at 66 percent.
The low coverage for OPV in the last 10 years is a reflection of the generally declining rate of immunization in the country over the last two decades. The rate of fully immunized children—those who received one dose of BCG, three doses each of OPV, DPT, and Hepatitis B vaccines, and one dose of measles vaccine before reaching one year of age—has been declining by an annual average of 1.22 percent from 1995-2018.
The lowest rate of fully immunized children was recorded in 2018 at only 66%.
Among the regions, Eastern Visayas recorded the lowest OPV coverage with only 59 percent in 2018. CALABARZON and Cagayan Valley followed with vaccination coverage of 61 percent and 62 percent, respectively.
In the National Capital Region (NCR), Makati City had the lowest OPV coverage with less than half or only 46 percent of children one-year-old and below given the three doses of the vaccine. San Juan City and Manila also had the lowest OPV coverage in NCR, with 54 percent and 55.17 percent, respectively.
Dr. Vergeire attributed the low vaccine coverage in the country to several factors, among them the so-called vaccine scare.
“Mothers do not have time to have their child vaccinated. There’s the vaccine scare, meaning parents have no confidence. And then of course, the supply side for the health human resources in local stations,” Vergeire said.
Low OPV coverage means that the risk for poliovirus transmission in the country is high, especially with the discovery of the vaccine-derived poliovirus in the environment.
“But it is not just because there is that environmental sample,” Vergeire said. “It has to go with the other factors like we have low coverage for immunization for oral polio, and also because of sanitary conditions.”
She also added that “weak surveillance” of individuals who exhibit symptoms of polio, particularly acute flaccid paralysis, in communities and hospitals contribute to the high risk for poliovirus transmission in the country.
To address the low immunization rate, the DOH has introduced such interventions as boosting the rate of OPV immunization in local health centers, heightening the surveillance of Acute Flaccid Paralysis or symptoms of polio, and massive information campaign.
The health department started a synchronized polio immunization last August in Manila, which will eventually be expanded to the whole of Metro Manila and other regions.
The first round of polio vaccination was done in Manila last Aug. 19 while the second round will be administered to the rest of the region in October. The third round will be done in the whole of Metro Manila and Regions III and IV-A in November.