MANILA — This week saw conflicting points of view on whether or not the Philippines had already seen the second wave of COVID-19 infections or remains on the first wave of the outbreak.

It was the country's health chief himself, Health Secretary Francisco Duque III, who made the statement that the country was already on the second wave - a remark since taken back after the Palace asserted the country was still in the first, with the health department later backing the clarification.

• Duque: Philippines now on second wave of COVID-19 outbreak
• DOH sorry 'for confusion,' says PH still in 1st wave of COVID-19 transmission

Explaining the science behind this, Dr. Mary Grace Dacuma, a molecular epidemiologist and professor at the University of the Philippines (UP) Los Baños, said the Philippines is still on its first wave of the COVID-19 outbreak simply because the country’s first confirmed cases who were infected abroad should not have been counted as a wave.

In a briefing paper released by the UP COVID-19 Pandemic Response Team, Dacuma also talked about local transmission.

She explained that the three Chinese nationals who tested positive for COVID-19 in late January to early February are considered “index cases.”

“The index cases, especially those that did not cause local transmission, do not form part of the epidemic wave,” Dacuma said, contradicting Dr. John Wong, the first to say the country was already seeing a second wave of infections.

Wong, founder of public health research firm Epimetrics, is a member of the sub-technical working group on data analytics of the Inter-Agency Task Force on COVID-19 and is likely the source of Duque’s information on the supposed second wave of the outbreak. He was asked to explain the second wave during a DOH briefing.

• READ: CODE RED: Philippines' coronavirus cases rise to 6, DOH confirms local transmission

Dacuma, a Ph.D. graduate from the London School of Hygiene and Tropical Medicine, explained that the “flat line” or the lull after the index cases were monitored in the country was merely because of the incubation period.

COVID-19’s incubation period is around 5.2 to 14 days. This is the time when the virus is infecting a person but has yet to manifest symptoms.

Wong had said the lull was the end of the first wave. But Dacuma explained, it is something that should be expected at the start of an epidemic.

Dacuma said the peak of an epidemic curve is when the “net increase in the number of active cases is starting to decline.” This is again contrary to Wong’s earlier explanation that the peak happened on March 31, when the country recorded 538 new COVID-19 cases.

As seen in the graph below, the number of active cases, which refers to patients still undergoing treatment, continues to rise.

“Eventually, there will be a reduction in number of cases (where the number of infected people recovering will be higher than those becoming infected). Then there will be a point where there are no more cases. That’s when we know the epidemic has stopped,” Dacuma wrote.

“That curve from the rapid rise of local cases to reaching the peak to reduction in number of cases to extinction of an epidemic is one epidemic wave. I did not include the index cases that started the epidemic in the “wave.” They acquired infection elsewhere out of the country,” she said.

Wong said the country has been flattening the curve already or slowing down the virus since it has been averaging 220 new cases in the last 5 weeks, but other experts have questioned this.

Dr. Anthony Leachon, Inter-Agency Task Force (IATF) adviser, also noted that the first few cases were index cases and that the country has not flattened anything.

• 'We have not yet flattened the curve': IATF adviser says PH still in coronavirus first wave