In charts: Covid-19 cases surge across four metro cities, growing faster than previous waves

In India, Covid-19 cases have spiralled up in the last fortnight of December, with experts saying this could be the beginning of a third wave of the pandemic in the country. The latest surge is steep and growing faster than the previous two waves.

During the summer when a deadly second wave swept the country, it took 27 days for daily cases to grow from 800 to over 2,000 in Mumbai. This time, it has taken just five days for cases to multiply to this level.

A comparison of four metro cities shows that Delhi has recorded the highest growth in positive infections in this period, while Mumbai has recorded the steepest growth in test positivity rate – or the number of positive cases per 100 samples tested. High test positivity indicates more spread of the virus in the community.

On Wednesday, Mumbai recorded 2,510 fresh Covid-19 cases, a 10-fold jump since December 15. In the same period cases in Delhi rose from 45 to 923, a 20-fold surge. In Kolkata, cases have risen by 2.7 times, and in Chennai by 2.3 times.

“I think this is the start of the Omicron wave in India, which a number of us had believed would happen around early January,” said Gautam Menon, professor of Physics and Biology at Ashoka University. To confirm that the current surge is being driven by the Omicron variant, India needs appropriate tests and genome sequencing at a scale that is not being done yet, he added.

While a majority of Covid cases remain mild across all four metros, Delhi and Mumbai have seen a rise in the absolute number of hospital admissions. However, the percentage of Covid patients requiring hospital care – currently 10% in Delhi, and 14.5% in Mumbai – is lower than the estimated 23% seen across the country during the second wave.

Professor Sundeep Juneja, Dean of School of Technology and Computer Science at Tata Institute of Fundamental Research, said the rest of India is soon likely to follow the trends seen in Delhi and Mumbai.

“If the new variant has started spreading, it is a matter of days before it reaches other parts of the country,” Juneja said. “Delta took a few weeks, and the new variant is even more transmissible.” First detected in India in late 2020, the Delta variant of the coronavirus had caused the second wave of the pandemic in the country in the summer of 2021.

Juneja and his colleagues are working on a mathematical model to predict Covid-19 growth in India in the coming months.

Positivity rate

In Mumbai, the test positivity rate stands at 4.8%, up from 0.5% a fortnight ago. This is the steepest rise for any city in India in the last two weeks. On Wednesday, Maharashtra health minister Rajesh Tope said the government may consider introducing further restrictions, if the positivity rate crosses 5%.

In Delhi, the positivity rate rose from 0.09 to 0.89% between December 15 to December 29, in Kolkata from 1.4% to 2.4%, and in Chennai, it rose negligibly from 0.8% to 1%.

For now southern states have not shown a spike in the positivity rate, but Menon said “it is a matter of time before we see that surge”.

The Ashoka University scientist added, “Given the experience of other countries, such as South Africa and the UK, there seems to be no way to avoid what they have experienced, although we may hope that a combination of a recent infection from the Delta wave and our vaccination programme, which has ensured that more than 60% of the eligible population has received both doses, will help protect those infected from adverse outcome.”

In terms of testing, Delhi is carrying out more Covid tests than Mumbai although it has a smaller population. The capital has been consistently conducting over 55,000 tests daily, of which 87-90% are through RT-PCR, or real-time polymerase chain reaction – higher than the Central government norm of 60%.

Considered the gold standard for Covid-19 testing, RT-PCR is known to have a better sensitivity to detect the virus compared to rapid antigen tests, which are less sensitive but produce faster results.

In Mumbai, daily testing has risen from 30,000 to over 50,000 in the last two weeks but RT-PCR accounts for 70-80% of samples. Dr Jeetendra Jadhav, medical officer in the city’s L-ward, said they are now trying to raise RT-PCR tests to over 90% of total samples.

Kolkata, which saw a brief spike in Covid cases in October soon after the Durga Puja festival was held, is again seeing a rise in the past week. The city is testing 15,000-17,000 people a day, with RT-PCR accounting for 55-64% of total tests over the last week.

Chennai is testing close to 18,000 people a day, which rose to over 19,800 on Wednesday. Tamil Nadu does not conduct rapid antigen tests, hence, 100% of its samples are tested through RT-PCR, which increases the chances of detecting Covid-19 cases.

Reproductive value

Data from the Institute of Mathematical Sciences, Chennai, shows the Reproductive value or R value, which signifies the number of people one Covid-positive individual transmits the infection to, stands at an estimated 2.54 in Delhi for the December 23-29 week. This means one Covid-positive individual in the city is infecting more than two people. An R value above 1 signifies a high degree of circulation of the virus.

In Mumbai, R value is 2.01 for the December 23-28 week. For Kolkata, it is 1.13 for December 26-29, and for Chennai, it is 1.26 for December 26-29.

Professor Sitabhra Sinha at the institute said the R value has been steadily rising for all Indian metros in the last few weeks. The R value is high in Bengaluru and Pune as well – it was an estimated 1.04 in Bengaluru for December 21-24, and 1.11 in Pune for December 23-26.

Hospitalisations

Hospitalisation numbers have also begun to inch up, several doctors said, although fatality rate continues to remain low.

Dr Srinath Reddy, President, Public Health Foundation of India, said while it is good news that deaths are low, high transmissibility may lead to a rise in hospitalisation in absolute numbers. Ashoka university professor Menon agreed. He said a stress on the healthcare system similar to the one India saw in the second Delta wave may be witnessed if the variant is allowed to spread without restraint.

Delhi has over 2,000 actively infected cases – 262 are hospitalised, 55 are on oxygen support, none on ventilator, data from the Delhi government shows. The hospitalisation rate is 10% of active caseload, while oxygen support is limited to 2.7% cases.

According to the Delhi government, 262 of 8,965 isolation beds in hospitals are occupied with suspected or confirmed Covid-19 cases, while there are no patients in Covid care centres or dedicated Covid health centres which are meant to admit mild to moderate cases. This leaves 98% of isolation beds vacant.

Mumbai has four times the caseload of Delhi. Active cases have doubled in the last three days in the city, now touching 8,060 – 14.5% are hospitalised. Of the 15,278 beds, almost 10% or nearly 1,500 beds are occupied. At least 186 patients are on a ventilator and 305 in ICU.

Dr Akash Khobragade, superintendent in St George’s Hospital, a dedicated Covid hospital in Mumbai, said from six patients in the hospital on an average in the first week of December, the hospital now has 43 patients.

“But very few require oxygen support and their saturation is easily maintained with 4-5 litres of oxygen per minute. This is much lower than what we administered during the Delta wave,” he said.

Dr Hemant Deshmukh, dean in KEM hospital, said the cases admitted in hospital are of mostly vaccinated patients suffering breakthrough infection.

In Delhi’s Fortis Memorial Research Institute, Dr Amitabh Parthi, director of internal medicine, said most patients being admitted to the hospital were above the age of 60. In the second wave, “even the younger age group required hospitalisation,” he said. “This time, we are able to manage them under home isolation. It is mostly senior citizens who have co-morbidities and a weak immune system who require hospital care despite vaccination,” Parthi said.

He added that those infected by the Omicron variant have fever and upper respiratory symptoms such as cough and cold, but “there is very little lung involvement or lower respiratory tract infection which means oxygen support is not needed in most cases”.

In West Bengal, 1.45% of 23,947 hospital beds earmarked for Covid care are occupied, according to government data. In Kolkata, while cases have started rising this week, there is slow spike in hospitalisations. The city has 2,912 active cases, 9.7% require hospitalisation, state government data shows.

Chennai has also not witnessed an increase in hospitalisations. Of 13,828 beds, 5.6% are occupied. Of 1,818 intensive care beds in the city, 78 are occupied, as are 374 of the 8,179 oxygen-equipped beds. At least 13,053 isolation beds are vacant in the city. Of 1,689 active cases, 26% are in hospital.