India will add four million more cases by May 1, says Giridhara Babu

A small proportion of the population might have reinfections due to waning antibodies. With newer areas seeing the surge in cases, we cannot rule out older variants spreading to these areas. There may be a dual problem facing the country. The old and newer variants might be in circulation in the uninfected regions in an earlier wave. Newer contagious variants might be spreading faster in urban pockets that had reached near-threshold levels of immunity, says Dr. Giridhara Babu.

Since the first COVID-19 case was reported in India, the next four weeks will be the defining period in terms of how successful India’s COVID-19 response will be in controlling the ongoing, uncontrollable surge in virus spread across many States. Dr. Giridhara Babu, epidemiologist at the Public Health Foundation of India (PHFI), Bengaluru explains the possible reasons for the sudden surge and how the steep increase in cases can strain the healthcare system leading to more deaths.

The increase in daily cases has been very steep — from over 12,200 cases on March 1 to over 1,26,000 on April 7. The doubling time has reduced from 504 day on March 1 to 115 on April 4. What do you think is the reason for the increase in cases in a short time?

First, outbreaks can occur only when we cross the critical threshold level of a pool of susceptible persons. Over a while, there has been an accumulation of susceptible persons. Second, the disregard for COVID-19 appropriate behaviour (CAB) is ubiquitous all over the country. Considering both as constant for all States in India, invoking Occam’s razor, the simplest explanation for the explosion of cases is the newer variants of concern. The newer strains are possibly more infectious, albeit not more lethal.

Can the exponential increase in daily cases be explained any other way other than a new, more infectious variant?

A small proportion of the population might have reinfections due to waning antibodies. With newer areas seeing the surge in cases, we cannot rule out older variants spreading to these areas. There may be a dual problem facing the country. The old and newer variants might be in circulation in the uninfected regions in an earlier wave. Newer contagious variants might be spreading faster in urban pockets that had reached near-threshold levels of immunity. It is a pity that we do not have sufficient data from the field to explain the distinction between these.

The reproduction number (R0) crossed 1 on March 21 and is 1.54 as on April 6. Will increasing R0 suggest that the daily cases will increase further?

Based on the projections by several modellers, including Prof Bhramar Mukherjee, Professor of Epidemiology at the University of Michigan, India will have nearly 1.8-3 lakh cases per day by May 1. The reproductive number is not decreasing, suggesting that there might be a higher number of cases in the next few weeks.

The active cases as on April 7 is over 9.05 lakh. If the daily cases continue to increase, what will be the number of active cases in the next few weeks/months?

The conservative projected estimates indicate that by May 1 India will have a total of over 17 million cases compared to 13 million now. Of the four million cases that will be added by May 1, two million will recover and we might have over two million active cases. Most of these will be asymptomatic cases. Hence what matters is what proportion of these will have severe illness or succumb.

Why are we seeing more cases in States such as Maharashtra and cities such as Mumbai, Pune, Bengaluru and Chennai that experienced more virus spread in the first wave?

As we have seen in multiple health programs, we have a skewed reporting problem in the country. States that report higher cases could be perhaps because they have a well-functioning surveillance system, and they test well.  Apart from infecting susceptible people, the high number of cases in metros compared to the first wave is indicative of a more contagious variant of the virus at play.

As on April 8, the seven-day average test positivity rate has touched 9% nationally, while it is 26.5% in Maharashtra, 17.2% in Chhattisgarh, 13.1% in Chandigarh, and 10.8% in Madhya Pradesh. Does this not suggest that a large number of cases are being missed?

Yes, we are missing cases. Some states are missing more than others. Even where done, a relatively higher proportion of rapid antigen tests (RAT) done in some States confounds this problem even more. In case of symptomatic illness, the RAT might be a useful tool to diagnose and isolate the persons quickly. It is not very sensitive in asymptomatic persons. Therefore, in Karnataka’s technical advisory committee, we recommend that RT-PCR be the test of choice in all persons with asymptomatic illness.  

Kerala has had a low seroprevalence, as suggested by ICMR and other surveys. After seeing a steady decline since the third week of January, an uptick in daily cases is seen in Kerala too. Will we see a surge in Kerala after a few weeks?

It is time that we speak of variant-specific thresholds of population immunity. If it’s the earlier variant, the low seroprevalence indicates that either a vast population is susceptible to the strain or the antibodies have waned over a period of time. For the newer variants, a vast majority of the people in the entire country, including Kerala, is susceptible, and case surge is a universal possibility in all States.

Is there any evidence that reinfections form a sizable fraction of cases reported now?

The antibodies might be waning faster, and therefore, a small proportion of persons infected might be having reinfections. There is no robust data to prove the proportion of reinfections in India. Epidemiologically, we need to monitor all those who are positive for the RT-PCR test (Ct values less than 35) more than 90 days from the first episode, regardless of symptoms. The ICMR database will have these details. Studies can be done by matching unique identifying information such as mobile numbers and names etc.

With bed shortages already reported in Maharashtra and hospitals fast filling up in other States, what will the hospitalisation trend due to the accelerated increase in daily cases be?

More cases occurring in a short period will adversely impact the utilisation of the health system. Even if we assume that 5-10% of the cases are severe, we need 15,000-30,000 critical care beds (with oxygen) by May 1, assuming the trajectory continues as it is now, resulting in 3,00,000 cases each day. This will severely strain the health system, especially in areas that do not have robust infrastructure and human resources.

Most States are already reporting increased numbers of daily deaths. Is it possible due to a new variant causing severe disease leading to death or due to healthcare facilities becoming strained and stretched beyond capacity?

There is a lag time of at least 10-17 days between case surge and death surges. Therefore, eventually, there will be a higher case fatality rate. The new variant might be more infectious but may not per se be causing more severe cases. As a result, there will be more cases in a short time. When the surge in cases is rapid, more persons with the severe disease might require critical care at the same time, resulting in a shortage of beds. This can increase mortality, as seen in most developed countries as well.

Without a national or Statewide lockdown, can increased containment measures including testing and tracing, adherence to COVID-appropriate behaviour, and increased vaccination coverage help reduce virus spread?

I have argued elsewhere that lockdown is a lazy policy optionat this stage and should not replace the much-needed enhanced containment measures. In addition to enhanced testing and timely isolation and quarantine, we need to follow the 3C strategy. These include prevention of crowding of any nature, minimising the spread in closed spaces, especially with poor ventilation, and preventing the transmission in close-contact settings through strict enforcement of mask wearing.

Published in The Hindu on April 10, 2021