Why rise in Kerala's coronavirus cases may not signal a new surge

Kerala is the only large Indian state where Covid-19 cases have been increasing consistently, but this is unlikely to be the start of a new wave in the state, say health experts

Over two weeks to July 11, average daily new Covid-19 cases in Kerala have increased by 15.2% and the state accounts for about one in every four new infections in India, data from Covid19India.org show. No other state outside the north east is showing such growth in new Covid-19 cases. The Indian Council of Medical Research has projected, in some scenarios, that India's third wave could begin as early as August. Could the rise in Kerala then be heralding the start of the third wave in India?

Unlikely, say health experts, pointing to the absence of a steep rise in infections. Cases are increasing at a slow rate in Kerala, despite the relaxation of lockdown restrictions and the rise of the more transmissible Delta variant in the state, they tell us. "Mobility is up, people are mixing and with Delta [variant dominating], the numbers should be shooting up, not stabilising," Rajeev Sadanandan, the chief executive of Health Systems Transformation Platform (HSTP), a New Delhi-based nonprofit, and Kerala's former additional chief secretary of health, told IndiaSpend.

Kerala had about half as many people with Covid-19 antibodies compared to the national average, ahead of the second wave, per health ministry data. "Hitherto uninfected pockets of people getting infected are sustaining the current high numbers," Gautam Menon, professor of physics and biology at Ashoka University, Sonepat, told IndiaSpend, adding that these are not increasing substantially.

The slow increase is due to Kerala's better case management, these experts say. The effects of the greater transmissibility of the Delta variant are being countered by better surveillance and the state's higher rate of vaccination. But given the high effective reproduction number of Covid-19 in the state---with one infected person infecting at least one other person, and more than 10% of tests returning a positive result--they caution that Kerala must track, trace and quarantine contacts of infected persons, increase testing and vaccination rates even further, and ease mobility restrictions slowly.

No exponential growth in Kerala's cases as seen in April-May

In April 2021, the average daily increase in cases in Kerala was exponential--reported cases went from 1,804 to 10,319 in just one month, an increase of 472%. In just five more days, cases had crossed the 20,000 mark, and in six days thereafter, the 30,000 mark, data show. By contrast, over the past two weeks, daily cases have risen by 15.2%, from 11,357 to 13,086.


 

"Epidemics surge and die down when a large number of people have been infected, just like a forest fire is controlled when many trees have been burnt. Then slowly, the epidemic starts picking up again, and builds into another surge, and the sequence continues," said Sadanandan. But the pattern in Kerala is different, he said. "When numbers start going up, people change their behaviour, and after a lag, the numbers start going down. When the numbers start falling, and people start dropping their guard, the numbers go up again. So talk of a third wave in Kerala is meaningless. The troughs and the crests are small, it is a slow burn."

This has been the case throughout the pandemic in Kerala, other than a spike in cases in April 2021, when the Delta variant began spreading in the state, Sadanandan said. Currently, because of the higher transmissibility of the Delta variant, cases have stabilised at a higher level, but the pattern remains the same. In the week to July 11, Kerala has reported an average 12,600 new cases a day.

 

 

Better surveillance, case outcomes and vaccination rates

One reason for the larger number of cases in Kerala could be the relatively lower seropositivity--or the prevalence of protective antibodies in people because of prior exposure to Covid-19--said Menon. Data from the third serosurvey conducted from during December 2020 show that 11.6% of those tested in three districts in Kerala had antibodies for Covid-19, while the national average was 21%.

"Serological studies for Kerala indicate that a relatively small fraction of the population may have sustained a prior infection, so there may still be a reservoir of people to be infected there and thus a possibility of an abrupt third wave", said Menon. "The state has not flinched from taking rigorous measures to cope with their case numbers, so may be able to manage any increase better," added Menon.

Kerala has managed its Covid-19 patients better, agreed Sadanandan. "[Case] numbers did shoot up in 2021. Kerala was still able to manage the availability of hospital beds, medical oxygen and ICU beds and avoid the panic that occurred in some other places," he said.

Kerala's case fatality ratio of 0.5%--calculated on the basis of cases with known outcomes, whether the patient has recovered or passed away--is less than half of India's 1.3%, data show.

Kerala also has better testing and reporting systems for Covid-19, IndiaSpend had reported in February 2021. It has tested at almost double the countrywide average, data show. Until July 11, India had conducted 317,567 tests per million, compared to 688,299 tests per million in Kerala.


 

Kerala has also reported Covid-19 deaths more accurately than other states, we reported in June 2021.

At present, it is likely that Kerala's seropositivity is much higher than when the third national serosurvey was conducted in the winter, as the Delta variant subsequently affected a lot of people in the state during the peak of India's second wave in April and May, said Sadanandan. "I suspect the seropositivity in Kerala will now be high, unlike last year. This, along with the protection from reasonable coverage of the first dose of vaccines, could be dampening the upward pressure of the virus," said Sadanandan. By July 11, Kerala has fully vaccinated nearly 16% of its adult population, while 43% have received at least one dose. Nationally, about 8% of adults are fully vaccinated and 32% have received one dose.

Kerala is also the only state, besides Maharashtra, that has its own genome sequencing programme to identify variants of the SARS-CoV-2 virus, which causes Covid-19. Kerala accounts for 11% of all SARS-CoV-2 virus genomes sequenced in India, behind only Maharashtra and Delhi, per a database maintained by the CSIR Institute of Genomics & Integrative Biology (CSIR-IGIB).

There is a lag in updating the database, per data shared by Vinod Scaria, a genomics scientist at CSIR-IGIB. In all, 5,400 samples from Kerala have been sequenced until now, Scaria told IndiaSpend.

Since March 2021, the prevalence of the Delta variant has been growing in Kerala. From no samples detected in February 2021, 88% of the samples tested in June 2021 were of the Delta variant, which is more transmissible than earlier Covid-19 variants. "The sequencing in Kerala is systematic compared to other states and is adequate," said Scaria. "But a state cannot remain isolated and all states need to do systematic efforts at sequencing to be able to identify emerging variants," he added.

Case reproductive rate, test positivity ratio remain high

Notwithstanding its better surveillance, reporting and case management, Kerala must remain cautious, experts say. "Kerala showed a brief spike in cases and its R number [effective reproduction number] continues to hover close to 1," said Sitabhra Sinha, professor of computational biology and theoretical physics at the Institute of Mathematical Sciences in Chennai.

The R number of a disease tells us the average number of people infected by one Covid-19 patient, on average, according to the World Health Organization. An R level lower than 1 means that the disease will eventually die out as one patient is not even infecting one other person, on average. An R level greater than 1 means the disease will grow fast. An R value equal to 1 would mean that the number of cases would continue at about the same level.

Currently, one Covid-19 patient in Kerala is infecting at least one other person, whereas the overall R value in India is less than 1, data show.


 

In addition, for the spread of Covid-19 to be considered under control, the test positivity ratio (TPR)--the ratio of the number of positive samples to total tests done--should be below 5%, according to the Johns Hopkins School of Public Health, US. A ratio higher than 5% means that many positive cases are being missed and could continue to spread the disease untracked, we reported in September 2020. Kerala's TPR halved from an average 24% in May 2021 to 12% in June, but has stayed at just over 10% since June 20 till date.


 

 

To control the spread of Covid-19, "Kerala should repeat what they did in May 2020. Every case should be traced, tracked, and the infected and primary contact should be quarantined. That is the only way you can deal with the Delta variant," Sadanandan suggested.

Kerala began easing mobility restrictions imposed to control the spread of Covid-19 in mid-June. On July 10, Chief Minister Pinarayi Vijayan reportedly announced that the easing of restrictions would happen in phases, based on the state's average test positivity rate.

As it reopens, the state must "Increase random testing, stress vaccinations and the removal of vaccine hesitancy, look for any unusual rise in cases and new reported symptoms among positive cases", suggested Menon. "Open up slowly, reserving closed, ill-ventilated spaces for the last and encourage outdoor interactions where possible," he added.