According to a new study, nearly one in five residents of the Indian capital Delhi have been infected by the novel coronavirus. Experts believe the number of cases could be even higher in the densely populated areas of the city.
The recent serological study conducted by the National Center for Disease Control (NCDC) showed that 22.86% of the 21,387 people tested for COVID-19 showed signs that they had been exposed to the virus.
Serological tests look for disease-specific antibodies in an individual and are carried out to estimate the spread of the disease in a population group.
"Since it is not possible to test everyone, the actual number of people infected by the virus is not known, especially because most of the patients are believed to be asymptomatic," Satyendar Jain, Delhi's health minister, told DW.
The study, which was conducted between June 27 and July 10, was aimed at assessing the COVID-19 spread in Delhi's 11 districts. The results showed that eight districts had over 20% infection rate. In a city with around 19 million inhabitants, this amounts to almost 4.4 million infections.
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Efforts to contain COVID-19
Experts say that serological surveys are effective as they help authorities make informed decisions about interventions that are needed to contain the disease.
"The survey findings show that in a city like Delhi, which has a high population density, a sizable population has been exposed to the virus. We can't let the guard down as a big part of the city's population is still vulnerable to the disease," V K Paul, who heads India's COVID-19 taskforce, told DW.
Virologist Shahid Jameel says the study shows that India has still not achieved "herd immunity" against COVID-19.
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Epidemiologists say that an infection prevalence rate of 40-65% could be sufficient to reach "herd immunity" against a viral disease.
The authorities in Delhi have decided to carry out a city-wide blood sampling in the first five days of every month starting from August. They hope that this strategy will help them assess the coronavirus intensity in the city and whether it has achieved the "herd immunity."
"The government plans to do it on a monthly basis across the city. It will cover both containment zones and normal areas, individuals from all age groups, with a sample size no less than the latest survey," said Health Minister Jain.
The Indian Council of Medical Research (ICMR) is contemplating whether other states should also conduct serological studies to respond better to the coronavirus situation.
With 1,238,798 coronavirus cases, India is the third most affected country in the world – behind only the US and Brazil.
On Thursday, the South Asian country reported the highest single-day spike of 45,720 coronavirus cases and 1,129 deaths. Overall, the country has so far reported nearly 30,000 coronavirus-related deaths. Maharashtra, Tamil Nadu, Gujarat and Delhi are the worst-hit states, with Delhi alone reporting over 125,000 cases and 3,690 related deaths.
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The infection rate in India has been rapidly rising since the government began to ease lockdown restrictions in mid-May. The country has logged a million new cases since then.
But the number of officially confirmed cases is falling in the capital. On June 23, Delhi recorded 3,947 new cases – the highest single-day tally since the start of the pandemic in India – and a month later, on July 22, the daily cases had dropped to 1,349.
Doctors say the patients' recovery rate, which stood at nearly 36% last month, is now 84% – much higher than the overall national recovery rate.
"Delhi has done quite well in recent weeks as authorities have ramped up testing and implemented social distancing rules. But we still have to be careful," Srinath Reddy, president of the Public Health Foundation of India, told DW.
The country of 1.4 billion has ramped up testing, carrying out nearly 10,000 tests per million people, compared to just a few hundred in March.
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