UNICEF says the Philippines is among the countries with the highest number of unvaccinated children, who are most at risk.

In the last five months, dozens of small children in the Philippines have died, with most of the recorded cases affecting those below the age of five.

The latest data from the Philippine Department of Health (DoH) on Sunday showed at least 862 cases nationally – 50 times more than last year.

At least 49 deaths have also been recorded since the beginning of the year.

Among those afflicted with the disease, medically referred to as pertussis, was Zion Torrepalma, just two-and-a-half months old. His parents said he spent weeks in the hospital because of his incessant coughing.

“It wasn’t the usual coughing sound, it was a wheezing kind of cough,” Danny Torrepalma, father of the infant, told Al Jazeera.

The respiratory tract infection is more commonly known as whooping cough because of its distinctive sound.

“It’s a continuous cough and then it’s followed by a prolonged inspiratory effort,” John Kelvin Gabot, a pediatric infectious disease specialist, explained.

Al Jazeera’s Barnaby Lo, reporting from Manila, quoted doctors as saying while whooping cough can be fatal, it can be treated if detected early. “And more importantly – it can be prevented by vaccination,” he said.

UNICEF said the Philippines is among countries with the highest number of unvaccinated children, and that could be partly blamed for the outbreak. The UN agency estimates that one million Filipino children missed routine vaccinations in 2021 when the COVID-19 pandemic was at its peak.

Due to the pandemic lockdown, many parents were unable to get the required shots for their children. Also, vaccine hesitancy was high.

DoH spokesman Albert Domingo told Al Jazeera during the pandemic, healthcare workers had to shift their attention to look after thousands of patients while forcing parents and their children to stay at home.

“And then you had issues on hesitancy,” he said.

As part of the government’s emergency response, healthcare workers are immunising children in communities where whooping cough cases have been confirmed, with plans to immunise five million more people by the end of the year.

With supply running low, many parents say they hope the vaccine arrives before the outbreak gets worse.