While a large number of people now have immunity against coronavirus due to previous infections or vaccination, a guarded approach is needed in terms of implementing restrictive measures to avoid a second wave-like crisis, experts said.
Dr Yudhyavir Singh, who has been managing the COVID-19 ICU at AIIMS New Delhi, said it is important to lift a few restrictions to resume economic activities when cases are low.
"However, one should not lower their guard ... Adopt a guarded approach in terms of following COVID-19-appropriate behaviour and implementing restrictive measures," he said.
Dr Singh added that Delhi may have already achieved herd immunity, considering the massive number of cases seen during the second wave.
However, Dr Pooja Khosla, senior consultant (Department of Medicine), Sir Ganga Ram Hospital, said the second wave of the coronavirus has taught us that cases can increase suddenly.
"There are warning signs from different parts of the world. In India too, a small increase in cases has been recorded. Infections can increase exponentially anytime. I think one should not assume anything and make all efforts to prevent a second wave-like crisis, which was a nightmare," she said.
"Opening everything is not appropriate ... everyone has been saying the third wave is a couple of days away," Dr Khosla added.
Pragya Sharma, professor (Department of Community Medicine) at the Maulana Azad Medical College, said a third wave is a certain thing but the number of people it will infect will depend on the implementation of preventive measures and the pace of vaccination.
"Even if there are breakthrough infections among vaccinated people, the severity will be less and hospitals will not be overwhelmed," she said.
Ms Sharma thinks the implementation of preventive and restrictive measures is an issue.
"People either don't wear mask or don't wear it properly. Most of them use cloth mask, which doesn't serve any purpose. There is hardly any vigil being maintained in crowded areas," she said.
After a devastating second wave of the coronavirus, people had started taking vaccination seriously. There would be queues at vaccination centres, but things have changed again. There is laxity on the part of the people, Dr Sharma said.
"At the inoculation centre at MAMC, only around 50 people are getting vaccinated a day, while we can vaccinate around 200 people every day. Vaccines are available but people are not coming forward," she said.
Dr Jugal Kishore, head of the Community Medicine department, Safdarjung Hospital, said around 80 per cent of people have immunity against the virus, either due to previous infection or due to vaccination.
"The Delta variant of coronavirus was responsible for up to 60 per cent of the cases during the second wave. We haven't observed any major difference between ''Delta'' and ''Delta Plus'' variant. So, a sudden spike in COVID-19 cases is not expected, until a new, more infectious variant emerges," he said.
Still, there is a percentage of people who have not been infected or did not develop enough antibodies despite getting vaccinated, due to various reasons. This set of people, which is almost 30 per cent of the population in Delhi, is likely to get infected.
"Two cases are possible - first, the virus continues to infect people slowly until heard immunity is attained, and second, a new, more infectious variant leads to an increase in cases till everyone has immunity. But it seems the third wave won''t be as severe as the second," he said.
With the lifting of restrictions, people from rural areas have started coming to Delhi or those who have remained isolated so far are stepping out. "If such people go to crowded places, then there is a possibility of a spike in cases," he said.
There is also a possibility that a new variant bypasses the immunity achieved through vaccination and previous infection. If that happens, it will a huge problem then, Dr Kishore added.
Niti Aayog member Dr VK Paul has also told the Delhi government to remain watchful as the next three months are important and unlocking activities can lead to an increase in COVID-19 cases.
However, a third wave of COVID-19 is "unlikely to be as severe as the second wave", Dr Samiran Panda of the Indian Council of Medical Research had told the Delhi Disaster Management Authority during a meeting on July 9.
He had mentioned that a substantial third wave would be plausible if any new, more infectious variant of the coronavirus emerges and escapes prior immunity in the absence of adequate lockdown measures.
Dr Panda had suggested that vaccination efforts be ramped up to strongly mitigate the impact of a possible third wave.
Delhi battled a brutal second wave of the pandemic that claimed a massive number of lives, with the shortage of oxygen at hospitals across the city adding to the woes.
On April 20, Delhi had reported 28,395 cases, the highest in the city since the beginning of the pandemic. On April 22 the case positivity rate was 36.2 per cent, the highest so far.
The highest number of 448 deaths was reported on May 3.
The capital has recorded 2,369 cases of the coronavirus in the last 30 days (since June 24), 79 cases a day on an average.