Jakarta. Almost half of Jakarta's 10 million population has had Covid-19 at a point in time since the pandemic began last year, a serology survey revealed on Saturday, stoking hopes that the capital would soon reach the elusive herd immunity against the disease. 

The survey, conducted by Jakarta's health department with help from researchers from the University of Indonesia, the Eijkman Institute for Molecular Biology, and CDC Indonesia on  March 15-31, found that 44.5 percent of the capital's population had the antibody for SARS-CoV-2, the novel coronavirus that caused the pneumonia-like disease, in their body.

That indicates that more people in the capital had been exposed to the virus at some time in the past, seven times greater than the official data suggested. Jakarta's official record only showed more than 649,000 people in the capital, or about 6.1 percent of its population, have had Covid-19, with 9,349 of them died from the disease.

Experts have long suspected the real figure for the Covid-19 pandemic in the capital was higher than the official record indicated, especially with the city burial data showed an unusually high number of burials with biosecurity protocol. 

The latest survey confirmed the extent of the pandemic in Jakarta, Widyastuti, the head of the city's health department, said. 

“Through this survey, we can estimate the proportion of Jakarta residents who the SARS CoV-2 virus has infected, whether confirmed by PCR tests or not," Widyastuti, referring to the polymerase chain reaction test, a golden standard for Covid-19 virus diagnostic, by its initial. 

"We can also see a complete picture of the pandemic situation in Jakarta. So, the handling and control strategies can also be adjusted," she said. 

Serology Survey

Pandu Riono, an epidemiologist from the University of Indonesia, who was involved in the study, said that the researcher found almost half of Jakarta's population had been infected with Covid-19 but likely without symptoms, which allows them to remain undetected.

According to the study estimation, 4.7 million out of 10.6 million Jakarta residents have had Covid-19. 

The study also found some groups are more susceptible to catching the virus than others. 

Most of the infected people aged 30-49 years, Pandu said. Infection in the female group was higher (47.9 percent), and the unmarried group had a lower risk of infection (39.8 percent).

“People in densely populated areas are more susceptible to Covid-19 infection (48.4 percent). The higher the body mass index, the more infected, in this case, overweight (52.9 percent) and obese (51.6 percent). People with high blood sugar levels are also more at risk," Pandu said in a virtual press conference on Saturday. 

The researchers conducted the serological survey using a stratified sampling method, taking blood samples from 5,000 people in 100 urban wards in six of Jakarta's city districts. 

The participants include 4,919 people aged 1 year or older —  with those in the age group of 1-14 years accounted for 21.6 percent of the participants, 15-49 years (52 percent), and 50+ years (26.4 percent). About 54 percent of the participants were female, and 46 percent were female.  

Herd Immunity

Jakarta Governor Anies Baswedan said that with close to half of the city population had Covid-19 antibody, he hoped that he hoped the city would achieve herd immunity soon.

"This [study] means that half of the population in Jakarta already has an exposure. Hopefully, there will be immunity against Covid-19," Anies said during the virtual press conference.

The World Health Organization estimates that 60 percent of the population having the antibody against the SARS-CoV-2 virus should be enough to establish herd immunity against Covid-19. 

Anies said the city would continue to accelerate the vaccination drive in the city to ensure more people are protected against the virus. So far, 5.4 million people in the capital have received at least one shot of the Covid-19 vaccine. 

Still, Pandu said a hed immunity in Jakarta could remain elusive as the city would see many visitors from parts of the country with lower vaccination or immunity level. 

“Herd immunity in Jakarta will be more difficult to achieve because Jakarta is an open city with high intra- and interregional mobility. Consequently, all residents who are active in Jakarta, both Jakarta residents and migrants, must have immunity, or been vaccinated, that can overcome all variants of the virus," he said.

He said there's a possibility that Covid-19 would become endemic and said the city must get used to assessing risks and maintaining discipline health protocols in everyday lives.