The second wave of coronavirus in Delhi is likely to peak within a week after possibly hitting a positivity rate of 50 per cent before the numbers start to go down, senior medical experts said on Monday.

Dr Jugal Kishore, the head of community medicine at Safdarjung Hospital, said, "The virus spreads from person to person in close proximity. Over the last few months, people have been meeting each other at a greater pace without following Covid-appropriate behaviour. The results are before us."

Citing the findings of a serosurvey conducted in February, he said around 50 percent of Delhi's population has already been exposed to coronavirus, and there are "very few" cases of re-infection.

According to the fifth serosurvey, conducted between January 15 and January 23, around 56 percent of Delhi's population have developed antibodies against the deadly virus.

"Even if we say only 40 percent of people have been affected so far...Delhi may achieve herd immunity if 30-35 percent of the remaining population is exposed to the virus," he said.

When a large part of the population develops antibodies and becomes immune to the virus, the chain of transmission is broken, and this is called herd immunity.

Dr Kishore said, "Delhi is likely to hit the peak of the second wave within a week", considering the exponential increase in cases.

Dr Yudhvir Singh, Assistant Professor of critical care at the All India Institute of Medical Sciences, said this Covid-19 wave is nearing peak in Delhi and the next week is going to be crucial.

"The positivity rate may as well touch the 50-percent mark," he said.

Cases will start receding by April-end and the situation will be comparatively better by the second week of May, Singh, who is a member of the "COVID Clinical Management Team" at AIIMS, said.

Asked about the reasons behind such a high number of cases in Delhi this time, Dr Singh said people let their guard down and didn't take proper precautions at a time when it is likely that the second wave was being fuelled by the highly infectious "double mutant" strain of the virus.

"Entire families are turning out to be positive. Ninety percent of the people threw caution to the wind ... didn't follow Covid-19-appropriate behaviour," he added.

Another reason is that a large number of non-Delhi residents have been coming to the national capital for treatment. They comprise some 30 percent of all COVID patients admitted in hospitals here, he said.

He said, "The virus will evolve with time and may become weak or strong, anything is possible.

"Most viruses tend to become less deadly after mutations, he added. The number of people getting vaccinated in the coming months will also determine how severe the situation will be," he said.

Dr N K Ganguly, the former head of the Indian Council of Medical Research, however, said the capital might have "hit the peak already" of this wave of coronavirus.

"The cases will start coming down next week. Similar trends (positivity rate and death rate) were witnessed in the US when it was grappling with a second wave of Covid-19," he said.

Dr Ganguly said several superspreader events, including the Kumbh, farmers' protests, weddings and election rallies, led to the present situation in Delhi and elsewhere.

The mutant virus is attacking children and younger populations in larger numbers, he said.

Delhi recorded over 25,500 cases on Sunday, the highest single-day tally since the pandemic began ravaging countries.

The city has registered 1,46,934 cases in the last 10 days. The positivity rate has shot up from 7.79 percent on April 9 to 29.74 percent on April 18.

Meanwhile, hours after a weekend curfew ended Monday morning, Chief Minister Arvind Kejriwal announced a six-day lockdown, till 5 am on April 26, in a bid to contain the spread of the virus.

He said Delhi's health system is under stress but has not collapsed yet despite around 25,000 cases coming up every day.

Hospitals in the city are grappling with shortage of oxygen supply and crucial drugs.

On Sunday, the CM said less than 100 ICU beds were available for coronavirus patients in the city, even as the government explored options to set up Covid hospitals in schools and Covid care shelters in gated housing societies.