Nearly half of all Jakartans may have had Covid-19, some 15 times the reported figure, according to a recent seroprevalence survey that suggests that many of the cases were asymptomatic.
THE University of Indonesia’s School of Public Health, the Eijkman Institute for Molecular Biology and the Jakarta administration conducted antibody tests on 4,919 people above the age of 1 from around 100 subdistricts of the capital’s five municipalities and the Thousand Islands regency from March 15 to 31.
The study found that 44.5 per cent of participants had developed coronavirus antibodies. Some 81 per cent of participants with antibodies had never been tested for Covid-19 and 63 per cent had never experienced symptoms.
Jakarta, with a population of about 10.6 million people, had a cumulative confirmed case tally of 382,055 as of March 31. Covid-19 cases are confirmed through PCR testing. If this pattern has held, it is possible that 4.7 million Jakarta residents have had the virus, with only 8.1 per cent of cases having been recorded, the survey suggested.
“This is the most important bit, that most of the infected people that later formed the antibodies neither experienced symptoms nor were detected by the official tally,” University of Indonesia epidemiologist Pandu Riono, who was involved in the study, told the Jakarta Post on July 13.
“[From the survey] we can estimate how many Jakartans have had the coronavirus, but the testing conducted was not enough to detect them,” he added.
Jakarta has the highest rate of Covid-19 testing in Indonesia, higher than the World Health Organisation standard of one test per 1,000 people per week. Jakarta now conducts 20 tests per 1,000 people per week, up from seven tests per 1,000 people per week in March.
The Jakarta seroprevalence study was not the first of its kind in the country.
In East Java, a group of scientists from Airlangga University and Japan’s Kobe University tried to estimate how many asymptomatic Covid-19 cases had occurred in the population through a serosurvey whose results were published in the PLOS One peer-reviewed open-access scientific journal on May 6.
The survey used antibody tests with a sensitivity and specificity higher than 90 per cent on blood samples taken from June to December of last year from 1,819 individuals above the age of 16 from two communities and one medical research centre in Surabaya and one private hospital in Jombang. Almost none the subjects reported having had Covid-19 symptoms.
About 11.4 per cent of the participants had developed immunoglobulin G (IgG) antibodies, which commonly appear after Covid-19 infection.
“We don’t know for sure why they developed their antibodies. However, what we can say is that the antibodies they developed are commonly found after Covd-19 infection,” said Laura Navika Yamani, one of the co-authors of the study and an epidemiologist at Airlangga University.
As Covid-19 antibodies also develop after vaccination, Laura suggested that any future seroprevalence surveys be conducted on vaccinated populations to ascertain the quantity of antibodies produced after receiving certain vaccines.
Both the Jakarta and East Java studies were conducted before the COVID-19 vaccine drive was expanded to the wider public last month. The government began vaccinating health workers in January. Public sector workers and the elderly followed a month later.
But such seroprevalence surveys have limitations, experts say. Larger populations are often so diverse that surveys struggle to capture the full picture and how antibody levels usually decline months after infection.
Masdalina Pane of the Indonesian Epidemiologists Association (PAEI), who was not part of either of the studies, noted that the accuracy of antibody testing had been widely questioned.
She said it could be advantageous if a large number of people had developed Covid-19 antibodies because they would likely be protected from the virus.
“This would only become a problem if, at the same time, the number of new confirmed cases remained high. Because that could mean reinfections,” she said, adding that antibody levels usually declined three months after the initial infection, providing a window for reinfection.
National Covid-19 task force spokesperson Wiku Adisasmito did not comment directly on the serosurveys but urged people to get vaccinated as soon as possible and maintain health protocols both before and after vaccination.
“The government will continue to provide vaccinations to achieve herd immunity against Covid-19,” he said.
THE JAKARTA POST/ASIA NEWS NETWORK