If the Indonesian authorities failed to take drastic measures to slow down the spread of COVID-19, the country could have tens of thousands of cases by April, or shortly before Idul the Fitri holiday, scientists have warned.

Disease surveillance and biostatistics researcher Iqbal Ridzi Fahdri Elyazar and his team at the Eijkman-Oxford Clinical Research Unit (EOCRU) have used the geometric sequence method to see, “how much time it would take for the number of cases to double in Indonesia”.

Based on their calculations, Indonesia could be grappling with up to 71,000 COVID-19 cases by the end of April.

Iqbal and his team noted that the doubling time for Italy and Iran, which currently have the highest COVID-19 death toll, was five and seven days, respectively. The doubling time, they added, would be longer for countries that have taken a rigorous approach to contain the outbreak. South Korea, for example, had a doubling time of 13 days and China 33 days.

For Indonesia, the number of COVID-19 cases doubled in three days, jumping from 172 positive diagnoses on March 17 to 369 on Friday.

“The shorter the doubling time, the more dangerous it is,” Iqbal told The Jakarta Post on Friday.

The team decided to use Italy’s and Iran’s doubling times to map the possible exponential rate in Indonesia. By using this geometric sequence, it found that the number of confirmed COVID-19 cases could reach between 11,000 and 71,000 by the end of April.

This prediction, Iqbal said, was meant to push the government to take massive and effective measures to handle the outbreak and also to raise awareness about the importance of social distancing.

Doubling time, he said, depended on the ability of the virus to infect, the magnitude of the case findings and the effectivity of intervention.

“Seventy-one thousand cases might sound scary, but that is what would happen without proper intervention (…) The President has urged the public to practice social distancing and we hope everyone is listening to him so we can decrease the doubling time (…) We have to do it faster and more effectively.”

He added that clear, transparent information about the places visited by COVID-19 patients was important to reduce the exponential growth rate of the disease so that people can avoid these areas.

According to the projections of Hadi Susanto, a professor of Applied Mathematics at the University of Essex in England and the Khalifa University of Science and Technology in the United Arab Emirates, the peak of COVID-19 in Indonesia would be around Ramadan, which is expected to take place from April 23 to May 23.

Assuming that even after a lockdown is imposed and people are still working and conducting business as usual and there are only two groups of people, the healthy ones and the sick ones, 50 percent of the population could be infected within 50 days after the first case was announced by the President on March 2, he said.

“We use Jakarta as a sample with a population of around 10 million. At its peak, the virus could infect 50 percent of the population,” Hadi told the Post on Friday.

He went on to say that if there was no lockdown policy and people could easily enter and exit the capital, then “the pandemic will not reach a peak and the number of sick people will continue to grow”.

“This is my pessimistic prediction, formed with a simple mathematical model. And of course, I hope that I’m totally wrong,” he said.

Achmad Yurianto, the Health Ministry’s disease control and prevention director general, told a press conference on Friday that the government had prepared 1 million test kits for massive testing.

“Between 600,000 and 700,000 people are at risk [of contracting COVID-19],” he said, adding that only those with a greater risk of infection would get tested.

A group of researchers at the Bandung Institute of Technology (ITB) Center of Mathematical Modelling and Simulation previously estimated that the outbreak would end in the middle of April and infect some 8,000 people.

Nuning Nuraini, one of the researchers, said the team had used a parameter estimation model based on the spread of infection in South Korea, which has been praised for its aggressive prevention measures and widescale rapid testing.

One such measure was providing drive-through COVID-19 testing centers that were able to test thousands of people, catching the infections early and rushing patients to hospitals to curb the spread of the disease.

The ITB researchers’ modeling is more “optimistic” compared to others. However, on Friday, after the government announced that the nation had recorded 369 positive cases, Nuning said they could no longer use South Korea’s parameters to estimate the epidemic’s profile in Indonesia, as the confirmed cases here kept increasing significantly.

She added that the situation could be better and the rate of infection could be suppressed.

“But if our intervention methods are not effective, then the peak can shift, as Hadi explained. Everyone must work together to prevent the spread of the disease. If this doesn’t happen, then the number of cases will not decrease. The Spanish influenza pandemic killed one-third of the world’s population. Do not let that happen again.”

Meanwhile, according to Panji Hadisoemarto from Padjadjaran University’s School of Medicine and a senior researcher at the university’s Center for Sustainable Development Goals Study (SDGs Center), all the mathematical modeling of COVID-19 made by scientists was meant to provide the government with reliable information to estimate the disease’s transmission impacts and evaluate the effectivity of mitigation efforts currently being used.

“We have to make sure that intervention is effective and enforced; [the government should give] more than just a recommendation. And the faster the intervention, the better.”

Arya Dipa contributed to this story from Bandung

Editor's note: An earlier version of this article contained an error on the figure from the group of researchers in ITB. The figure has been corrected to 8,000, not 800,000 as previously stated.