The coronavirus pandemic is in retreat in India, with one major exception: Kerala. One in every five samples tested for Covid-19 in the southern state is turning out to be positive, a rise from one in eight samples until early August.

The state alone accounts for over 60% of daily fresh cases in India.

“This is an early warning signal,” said Dr Samiran Panda, head of epidemiology and communicable disease in the Indian Council of Medical Research. He pointed out that the pattern seen in Kerala – a drop in cases, followed by a temporary lull, and then a surge – indicates the third wave of the pandemic has begun in the state.

What explains the heavy caseload in Kerala?

Many have blamed the state government for creating a fertile ground for transmission by relaxing restrictions during the festival season. An uptick in cases began in July, when the number of new cases rose from about one lakh in the week before Bakri-Eid to 1.22 lakh new cases in the week after. A month later came Onam. From 1.34 lakh cases in a week leading to the festival, the case tally rose to 1.73 lakh in the week after.

However, other states too have witnessed large gatherings, and yet not seen a rise in Covid-19 numbers. So why is Kerala bucking the national trend?

Experts say the fresh surge in the state is an outcome of its own stringent prevention protocol against the virus. “Kerala is a victim of its own success,” said epidemiologist and physician Dr Chandrakant Lahariya. “It did not allow the virus to party in its state like the virus did in Uttar Pradesh or Madhya Pradesh.”

What seroprevalence surveys show

What Lahariya means is that Kerala was successful in controlling and slowing down the spread of infection, unlike other states where the virus rapidly rampaged through the population. A rapid spread led to health systems getting overwhelmed, resulting in a high number of casualties, but this also created immunity in the population faster. In contrast, controlling the spread allowed Kerala to keep its casualties under check, but left most of its population vulnerable to future waves of infection.

This view is based on the findings of the fourth national sero-survey conducted by the Indian Council of Medical Research. A sero-survey tests a sample population in a region to assess whether they have antibodies against a particular infection. The presence of antibodies indicates they may have been exposed to the infection even if they hadn’t developed symptoms of the disease.

A higher seroprevalence number in a state suggests infection spread rapidly among the population, while a lower number indicates a limited spread either because the state was able to limit the spread of the virus through effective pandemic-control measures, or the virus is yet to make an inroad in some pockets.

In July, the ICMR released the findings of its fourth national sero-survey, which showed Kerala had the lowest seroprevalence among all states, with just 44.4 % of its surveyed population having antibodies against the virus. Madhya Pradesh, at 79%, had the maximum population exposed to the virus. India’s national average was 68%.

Experts say the low seroprevalence in Kerala shows the state government’s measures for early diagnosis, contact tracing and curbs on movement helped restrict infection to a limited population. “Kerala has drawn out the epidemic over a longer period,” said Lahariya.

Since fewer people have been exposed to the virus in Kerala, and its vaccination coverage is only 21% of the total population, there is still a significantly large population at risk of Covid-19 infection. This explains why cases are rising here, while neighbouring states like Karnataka and Tamil Nadu, that have over 69% seroprevalence, are reporting lower case numbers.

Hospital visitors wear facemasks outside the Government Medical College in Thrissur soon after India's first confirmed case of Covid-19 was detected here. Photo: AFP

Kerala has reported over 40 lakh Covid-19 cases since the start of the pandemic in March 2020, the highest after Maharashtra.

Lahariya said based on the sero-survey findings, the reported Covid-19 cases, and state population, it is possible to arrive at an estimation of the number of unreported cases in each state. Kerala is reporting one in every six Covid-19 cases, much higher than the national average of one in 30 cases. Maharashtra is reporting one in 12 cases, while Uttar Pradesh is reporting one in 100 cases.

While Kerala is missing every five infected persons for one person it diagnoses, UP is missing 99 persons.

What the testing graph looks like

The Covid-19 pandemic arrived in India through Kerala on January 30, 2020 – a student who returned from Wuhan, China, was the first positive case in the state and the country.

Since then, Kerala took strong measures to control the spread of infection. It had among the highest testing ratios in India – five months after the first case it had tested 1.71 lakh people. That included over 46,000 health workers and hundreds tested at airports and ports. Even a breach in personal protective equipment of a health care worker meant a quarantine for 14 days.

Kerala’s strategy earned widespread acclaim with even the World Health Organisation taking a leaf out of its model.

The first wave of the pandemic peaked on October 24, when the state saw an active caseload of 97,417 cases. In April this year, Kerala recorded another surge and reached 4.45 lakh peak active cases on May 15. The active caseload flattened to a lakh in June. By July second week, cases began rising again, reaching an active case pool of 1.60 lakh by the end of the month, and crossing the 2 lakh-mark for the first time on August 28 in four months.

While the state government has claimed the high caseload is a reflection of its superior surveillance system compared to other states, recent data suggests there are shortfalls in testing.

The daily testing numbers dipped from over 1.90 lakh in early August to 1.20 lakh by mid-August. In the last one week, the numbers have risen back to 1.50-1.70 lakh tests. But, on August 30, the testing number fell again to 1.17 lakh.

As a result, the week on week positivity rate has risen from 10% on August 1 to 14% on August 14 and finally 18% By August 31. The positivity rate is the number of people testing positive for an infection against total tests carried.

Economist Rijo M John said the state needs to carry more tests to diagnose people early. “In the days leading to Onam the numbers of tests declined leading to less positive cases. A drop in fresh cases should not give false sense of security to people,” he said.

R-value and the spread of infection

Kerala’s daily fresh caseload is around 30,000 and is expected to grow further. A week on week analysis shows the effective reproduction number, called the R-value, which indicates how many people a Covid-19 positive person can infect, has shot beyond 1 in the last week.

If R-value stands at 1.4, it means 100 people can infect 140 people. If it is 0.9, 100 people will infect 90 others.

Sitabhra Sinha, from Institute of Mathematical Sciences in Chennai, said Kerala’s R-value dropped from 1.09 in the first week of August to 1.07 by mid-August, and touched 0.80 until August 23. Onam was on August 21. “Data for August 25 till August 29 shows the R value has risen to 1.33. It was not this high since April when R-value crossed 1.40 in Kerala,” he said.

John said decreased Covid-19 testing in the days leading up to Onam, followed by a sudden rise in testing and positive cases in the last week of August, explain the sharp variations in the number.

Some experts say if the R-value continues to rise, the future trend would be an explosion of cases. However, professor K Srinath Reddy, epidemiologist and president of Public Health Foundation of India, said that the R-value must not be considered in isolation while predicting patterns. “It is a trend indicator, but since there is an underestimation in the number of people actually infected, R-value must be seen in combination with other factors for analysis,” he said.

A rise in R-value, however, indicated a continued rise in cases in coming days in Kerala, he said. “Preventing super spreader events, wearing masks, and preventing the health system from collapsing is what Kerala must focus on.”

Can health systems cope?

Despite having a larger proportion of elderly population compared to the national average, and a higher burden of non-communicable diseases, Kerala has managed to keep its death count low. So far, the state has officially counted 20,673 Covid-19 deaths.

Kerala’s overall case fatality rate – number of people succumbing to the disease out of total number diagnosed – stands at 0.5%, significantly lower than the national average of 1.34%. The maximum fatality rate in the state is in Thiruvananthapuram district at 0.96%.

John said even if Kerala reports 45,000-50,000 cases, the public health infrastructure should be able to cope with hospitalisations. “That is due to fewer hospitalisations because of vaccine coverage,” he said, but warned that the state may have to go for full lockdown if the surge continues. “The weekend lockdowns and night curfews are unscientific. They do not help disperse crowds.”

After it saw a spike in Covid-19 cases post-Onam, the state has announced night curfew and weekend lockdowns from August 30. Except for these measures, economic activity is back to normal during weekdays. High economic mobility has increased transmission risk.

The state government, however, claimed that it has scaled up health infrastructure to prepare for a third wave. Chief minister Pinarayi Vijayan said the latest curbs were to flatten the steep rise in cases and prevent deaths.

Kerala has over 64,000 isolation beds in government hospitals, data from state’s official portal shows. Across all 14 districts, there are 57% vacant isolation beds. If private beds are counted, there is a 58.8% vacancy. But some districts have started reflecting a shortage in ICUs and ventilators.

Kollam has 94 beds in the Intensive Care Units and 62 ventilators in the government sector – all beds are full. Thrissur has no vacancy in ventilators and only one ICU bed available in government hospitals. At least six districts – Malappuram, Kannur, Kasaragod, Idukki, Kollam and Thrissur – have less than 10% vacant ICU beds in government hospitals.

The state government has empanelled 281 private hospitals and plans to utilise their beds in case government infrastructure is overwhelmed. As on August 31, there were 3,627 patients with severe Covid-19 symptoms, maximum in Pathanamthitta (551), Malappuram (537) and Thrissur (516).

This reporting was supported by a grant from the Thakur Family Foundation. Thakur Family Foundation has not exercised any editorial control over the contents of this article.