After reporting a significant drop in the number of Covid-19 cases for months, some Indian states have seen a sharp uptick in infections in February. The BBC's Vikas Pandey and Soutik Biswas report.
In early February, physicians in Amravati district, some 700km (435 miles) from India's commercial capital, Mumbai, noticed a sudden surge in the number of people suffering from Covid-19.
Life in this cotton-growing district in the western state of Maharashtra had almost returned to normal after the first wave of infections last summer. The ICUs of the 1,600-bed state-run hospital and half-a-dozen private hospitals were nearly empty.
"But everything changed in February," says Anil Jadhav, a local journalist. "And now there's panic in the district."
Since the beginning of February, Amravati has recorded more than 10,000 cases and over 66 deaths from Covid. More than 1,000 were receiving treatment for the disease this week. The positivity rate is in frightful double digits. Amravati and a few other districts in Maharashtra have been again locked down.
The hotspots in a district of 2.5 million people are mainly congested urban areas, say locals.
"We really don't know what the cause of the surge is. What is worrying is that entire families are getting infected. This is a completely new trend," Dr Shyamsunder Nikam, civil surgeon of the district, says.
A number of neighbouring districts have also seen a sharp uptick in cases and Maharashtra recorded nearly 9,000 cases on Thursday, the largest single-day spike in four months. It reported 80 deaths on the same day.
"People here have been not wearing masks. They have been attending unregulated mass gatherings such as marriages and campaigns for local elections. There is free intermingling of people, carriers are not getting isolated, and testing and tracking is low. This has led to this situation," Dr Sanjay Oak, a member of the state's Covid task force, told the BBC.
It's not just Maharashtra where cases have grown recently. Some areas in Kerala, Karnataka, Telangana, Madhya Pradesh, Chhattisgarh and Punjab states have also reported surges. This comes at a time when much of India is reporting a sharp fall in cases - with daily infections for the county falling to less than 20,000 from a peak of over 90,000 in September.
And that has baffled scientists, disease modellers and epidemiologist. The most common reasons given for the spikes in some states are the same as in Maharashtra - big weddings, people not wearing masks, reopening of cinema halls, gyms and swimming pools, and large political rallies in states like West Bengal where elections are due soon.
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Epidemiologist Dr Lalit Kant says a "false sense" of normalcy has "swept the country".
"We cannot afford to drop our guard and we have to be cautious about opening places of mass gatherings. Testing, tracing and isolation has to be again scaled up massively in all states - we cannot wait for things to get worse."
Dr Kant adds that the rise in the number of cases in some states was expected because it followed the global pattern. "We have seen spikes in several countries after a lull of two to three months."
Disease modelling expert Gautam Menon agrees that the spike was expected.
"Modelling work and sero survey results would suggest that much of India should be still susceptible to the disease, so a resurgence of the sort we are seeing is not very surprising."
But why is the resurgence happening only in a handful of states, particularly in Maharashtra?
Mr Menon says the only reasonable conclusion is that surveillance in these states is stronger and that a similar rise in other states may simply have gone undetected so far.
Another possible reason, experts say, could be mutation. Viruses often mutate to change their genetic code, which is like their instruction manual. Mutations allow viruses to spread faster and, in some cases, render antibodies less effective.
This has been seen in the UK, South Africa and Brazil - new variants from these countries have spread much faster in large clusters. Cases linked to these strains have been detected in India, but there is no evidence yet that they have spread in the community. "This is at once good and bad news," says Mr Menon. "[The absence of foreign variants in the community] is good because they are known to spread faster and can potentially escape immunity generated from a prior infection . Bad news because we know little about whether the Indian variants may behave similarly."
Several Indian states have started genome sequencing to identify new variants. Officials have said hundreds of new mutations have been identified.
"But that is not enough to attribute the surge to mutations," says prominent virologist, Dr Shahid Jameel.
He adds that isolated mutations happen with viruses, but we need more data and research to come to a definitive conclusion. "Unless there is enough data to link a new variant to large epidemiological clusters, we can't attribute any surge to mutations."
So, Dr Jameel says, at present, mutations can't be blamed for the surge in Amravati and other places, though "it could all change in a matter of days".
"We may see more localised surges in different part of the country in the coming weeks, and the only way to stay on top of the situation is to be vigilant. We need to be concerned but we are not at a stage where we need to panic," he adds.
Experts say that India needs to scale up genome sequencing to quickly identify new variants that can potentially be more dangerous. Doctors also say that this is the only way to stop a new variant from wreaking havoc in India, like the Kent variant did to the UK.
Dr A Fathahudeen, who is part of Kerala's Covid task force, says his state has been reporting a persistent rise in cases in the past few weeks, but it's largely because of improved testing. "The RT-PCR testing is considered to be the gold standard of testing and around 75% of testing is now being done through this method in the state."
He advises other states to follow the same measures. "Not finding new cases doesn't mean Covid has gone away. It simply means that the virus is burning through the population until it finds weaker victims like the elderly and people with co-morbidities."
Experts say a strategy involving faster vaccination, genome sequencing and an increase in testing are the only way to stay ahead of the virus. "Otherwise, surges in other states are inevitable," says Dr Fathahudeen.
And that will be a "terrifying scenario" for healthcare workers who are tired and exhausted after battling the pandemic for a year now.
"There's no doubt that hospitals are more prepared now, but we are at a delicate phase at the moment and missteps can again put pressure on healthcare workers, and the population too.
"Let's hope we don't get to that point," he adds.
Data analysis and charts by Shadab Nazmi