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MANILA - "A lot" of mothers are refusing to vaccinate their children, a health official warned Tuesday, with about 11 percent of moms in Manila refusing to participate in an immunization campaign against polio last month.

Health Assistant Secretary Maria Rosario Vergeire said most of the mothers who refused to vaccinate their children come from the "poor sector of the society."

"It has been reported ever since 2016 that a lot of mothers are already refusing vaccination. We don’t know why, we have asked some, of course there would be this controversy, others would be not believing these vaccines," she told ANC's Early Edition.

Last month, the Department of Health announced that the country has recorded its first cases of polio after 19 years of being declared polio-free due to plummeting immunization coverage. A student in Manila had also died of diphtheria, while government earlier declared a national dengue epidemic and measles outbreak.

Vergeire said the agency conducted an immunization campaign against polio last month in the nation's capital, where "about 11 percent" of the mothers refused the vaccine.

"The mothers were saying they don’t need it. The mothers were saying the child already had the vaccination before. These kinds of reasons have been given to us when we went to the city of Manila," she said.

Vergeire, however, said children up to 5 years old must be given the vaccine.

"We are going to provide immunization irrespective of their immunization status. It has no side effects, no bad taste for this oral polio vaccine. It is safe and has been used ever since the 1970s," she said.

Vergeire, meantime, said dengue cases are "becoming manageable."

"We are comparing it with the epidemic and alert thresholds that we have and we can see cases are really going down," she said.

There was also a rise in vaccination against measles, following the DOH's campaign against the illness due to the outbreak, she added.