Chennai: India witnessed a peak of one million active COVID-19 cases in mid-September 2020, followed by a consistent decline, slowing to 0.15 million as of February 7, 2021. Other large states with high COVID-19 caseloads such as Maharashtra, Uttar Pradesh and Tamil Nadu have seen a similar trajectory. Kerala, however, saw active COVID-19 cases peak over a month later, in October 2020, and this has not been followed by a noticeable decline.

India's first three COVID-19 cases were discovered in Kerala on January 30, 2020, when three medical students returning from Wuhan, China--where the virus originated--were identified by the state, isolated, tested and then hospitalised.

Two weeks later, on February 14, the first three patients had been declared recovered, and Kerala's finance minister Thomas Isaac tweeted, "Kerala has won battle with Corona Virus (sic)". "I'm hopeful we can declare Kerala as coronavirus-free by the first week of March," health minister K.K. Shailaja had said a week earlier.

That celebration was premature, but even as dozens more cases followed, Kerala seemed to have controlled the spread of the disease by early May 2020 through a vaunted contact-tracing effort. Its "patient movement maps", or flow charts tracing the steps of identified patients, were shared widely on WhatsApp. By the second week of May, Kerala was one of the world's COVID-19 success stories, down to under 20 active cases, even as numbers surged in the rest of India.

Then, cases began to rise as Kerala residents, stranded by the nationwide COVID-19 lockdown, began returning home by special trains and on repatriation flights from overseas. By June, active cases were up to 700. By July, this had tripled to over 2,100, and this would further multiply fivefold by August. As of February 7, 2021, Kerala accounts for nearly one in two active cases in India.

Does Kerala's differing COVID-19 trajectory point to its success or failure? The state government's COVID-19 adviser points to Kerala's particular demographics--densely populated, higher elderly population and higher prevalence of comorbidities--as well as claiming that the state may be reporting its true caseload more accurately than other states. Doctors and other experts agree with him only on attributing the rise partly to Kerala's initial success in controlling the spread of the virus. This meant, they say, that fewer people in the state had developed antibodies. And, they point out, Kerala let its guard down ahead of occasions such as Onam when large gatherings should have been expected.

Kerala's COVID-19 peak came a month after other large states

Kerala's rise in COVID-19 cases first began in mid-May when both inbound and interstate travel resumed, initially to facilitate return of stranded citizens. On May 7, the first repatriation flight arrived in Kochi. A week later, the first post-lockdown passenger train from Delhi arrived in Thiruvananthapuram. Within two months, over half a million Malayalis had returned to the state through various modes of travel. Two-thirds of the 9,776 cases reported in Kerala from mid-May to mid-July were of incoming travellers.

From then on, cases rose steadily, as in the rest of India. But where Kerala broke away from the rest was in its trajectory from September onward. While reported cases in most big states peaked in mid-September and then began to decline, Kerala's apparent peak came late, in October. This has not been followed by the strong decline reported in other large states, such as Maharashtra and Tamil Nadu.

As a result, Kerala at present increasingly dominates the COVID-19 news in India. Virtually one of every two new cases now is reported from India's 13th largest state by population.

Who let their guard down?

We asked experts what makes the trajectory of the virus so different in Kerala. Kerala is a victim of its own success, Rajeev Sadanandan, the state's former health secretary who is now the chief minister's adviser on COVID-19, told IndiaSpend. "Right from the last week of December, COVID-19 cases have been rising [again]. It stems from people behaving as if the situation is over," he said, "In the rest of the country, no one is wearing masks or practising social distancing, and looking at this, people in Kerala started behaving this way too. But since Kerala initially controlled the epidemic very well, [it has] a large pool of vulnerable people."

Further, Sadanandan said, "When people here saw images like in the Bihar election or the farmer agitation, where thousands of people were gathering with no consequences, they relaxed here too. Because of how well we had controlled the epidemic, they stopped taking the virus seriously. And now the virus is coming to extract its pound of flesh."

Is Kerala's current experience similar to the second waves seen in Europe or North America, then? Sadanandan disagrees. "In Kerala, the aim was always to keep the number of cases well below the surge capacity. The number of new hospitalisations remained the same every day, and this was a comfortable equilibrium. All through, we never had a raging epidemic. It was under control. We did not lose people because of not having hospital beds. But that comfort zone is lost now." Sadanandan, however, believes that the pandemic is on its way down in Kerala too. "The state is taking it very seriously. We feel that the last peak was over in the second week of September and cases are now coming down and plateauing."

Other experts also suggested Kerala's early success meant fewer people had developed immunity to COVID-19. "If you have a higher fraction of susceptible people in a population, then the effective 'R' value of the disease is going to be higher, meaning, on average one infected individual will infect more than one person. There is little doubt that Kerala's early success meant that relatively few people in the state had the disease and acquired some level of immunity. For example, the second national seroprevalence survey found only 0.8% prevalence of IgG [immunoglobulin] antibodies in Kerala by August. The larger fraction of susceptible people must certainly explain the current situation to some extent at least," Murad Banaji, mathematics lecturer at Middlesex University in the United Kingdom, who has been examining India's COVID-19 data, told IndiaSpend.

Doctors in Kerala agree that this must be part of the reason. "It's definitely true that this is part of the explanation," Arun Madhavan, a doctor of internal medicine in Palakkad, Kerala, who has been critical of the state possibly under-reporting COVID-19 deaths in the past, told IndiaSpend. "This has to be part of the reason for this mystery," Padmanabha Shenoy, a rheumatologist based in Kochi, agreed.

COVID-19 seroprevalence data from the three countrywide Indian Council of Medical Research (ICMR) surveys showed that there was consistently and significantly lower spread in Kerala than in many other parts of India. National sero-prevalence was at nearly 7% in August, while in Kerala it was lower than 1%, despite the state being one of India's most urbanised. Some big cities like Mumbai and Pune had already displayed sero-prevalence levels approaching 40% by then, in comparison. By December-January, national sero-prevalence was at nearly 22%, while in Kerala it was 11.6%, showing that while Kerala still trailed the national average, there had been far faster spread between August and December 2020.

It is, however, undeniable that fresh COVID-19 infections are cropping up in Kerala too, say experts. "Yes, the disease can spread more in "untapped" areas. However, that does not justify letting it spread and attributing the current failures to the mitigation success in the early phase," Bhramar Mukherjee, chair of biostatistics and professor of epidemiology at the School of Public Health, University of Michigan, who has studied the spread of the virus in India, told IndiaSpend. "You have to continue the mitigation through contact tracing and testing, so that the community viral load goes below a certain level and one can enter a state of containment. Look at Australia, New Zealand, Taiwan, Singapore, South Korea... They kept a careful watch on case counts. As soon as they saw a spike, they doubled down on prevention measures and contained the disease. This included massive efforts in tracking down superspreader events ," she added.

There were large gatherings in Kerala on Onam, through late August and early September, and then at Christmas and New Year, both Madhavan and Shenoy said, and no lockdown restrictions were instituted by the state.

Sadanandan offers one further explanation for Kerala's higher cases--that Kerala is doing a much better job of accurately reporting its true caseload than other states. That too cannot be a full explanation; even if other states were suppressing the number of mild cases, hospitalisations have dropped across the country, health ministry officials have said in press briefings, indicating a true decline.

Sadanandan also attributed Kerala's particularly high COVID-19 numbers to a few additional demographic factors. "Part of the reason is Kerala is very densely populated. The whole of Kerala is like one continuous city. The population of people who are over 65 years of age is also very high--the highest in the country. Seniors in Kerala are also much more mobile," he said. "The high rate of comorbidities and elderly population could mean that a greater share of cases become symptomatic, and so come to light in Kerala. In states with younger populations and fewer [persons with] comorbidities, these might have remained asymptomatic cases and been missed," Shenoy added.

Kerala is India's fourth most urbanised state and the third most densely populated, according to Census 2011. It does have a relatively older population, and advanced age is strongly correlated with worse outcomes in COVID-19 patients in India and worldwide, as IndiaSpend reported in November 2020.

People with non-communicable diseases--which become comorbidities in the case of COVID-19--are also at greater risk of severe COVID-19 illness. Kerala has a higher proportion of overweight and obese adults, measured by a body mass index greater than 25, than any other state among the 17 covered in Phase 1 of the National Family Health Survey, 2019-20. Kerala also has the highest proportion of adults with high blood sugar levels, and is behind only Sikkim and Manipur in terms of proportion of men with high blood pressure. All are risk factors for severe COVID-19 illness.

Experts, however, say these factors alone do not adequately explain why Kerala is experiencing such a different trajectory from the rest of the country.

"While it's possible, in principle, for [Kerala's] administrators to be correct [that early success with containment explains current high numbers], seroprevalence in other regions in India would have to be very high to explain this pattern. Substantial differences in previous transmission that might result in 10% seroprevalence in one place and 30% in another would be insufficient to result in subsequent spread being greatly reduced in the place with 30% seroprevalence. There are many examples (including, most recently, in Manaus, Brazil) where people thought previous transmission had resulted in "herd immunity", only to see cases rise subsequently," A. Marm Kilpatrick, professor in the Department of Ecology & Evolutionary Biology at the University of California, Santa Cruz, and a leading global expert on the pandemic, told IndiaSpend. "Other possible reasons for differences in cases that I believe would be at least as important as previous transmission and immunity include: differences in behaviour of people, due to media reports, previous exposure of friends and family, interventions, differences in the age range of people being infected (younger people becoming infected will result in fewer "cases" being detected), differences in testing capacity and ease in people being tested, and, more recently, the possibility of different viral variants," Kilpatrick said. Sadanandan, however, ruled out new COVID-19 variants as an explanation.

Kerala's current predicament could be as much about the state as the rest of the country. If relatively low early transmission does explain Kerala's continuing higher numbers, this could indicate that the disease spread much deeper and faster in other parts of the country than previously known. It would also mean that India's September peak and decline was not a result of successful mitigation, but rather a result of a runaway epidemic and the resulting immunity. The September peak and decline could either be explained by successful containment, or by near-herd immunity, Manoj Murhekar, director of the ICMR's National Institute of Epidemiology, and lead investigator of the ICMR's national sero-surveys, told IndiaSpend. "Personally, I would tend to be on the side of the latter explanation."

Whether Kerala succeeded in containing transmission or not, then, is intimately related to whether the rest of the country failed or not.

We welcome feedback. Please write to We reserve the right to edit responses for language and grammar.