Chennai: With the COVID-19 pandemic currently in decline in India, and repeated messaging from the government that the country seems to have seen lower mortality from COVID-19 compared to other countries, it might be time to examine how COVID-19 stacked up against other deadly infectious diseases in India.

By the end of 2020, India officially had just over 10 million laboratory-confirmed cases of COVID-19, nearly twice as many as cases of typhoid, tuberculosis, malaria and pneumonia in 2018 put together, according to government data. Further, there were more COVID-19 infections in India in 2020 than from most other communicable diseases in a normal year, our analysis of Global Burden of Disease estimates showed. While India seems to have seen lower COVID-19 mortality, COVID-19 deaths in India dwarfed those from other infectious diseases.

However, the true number of infections--including asymptomatic cases--was likely much higher, according to two government national sero-surveys. The results of a third national sero-survey (December-January) currently under way are not yet out, but a smaller increase in sero-prevalence can be expected, which would put the number of estimated COVID-19 infections by the end of 2020 in the range of over 75 million at the lowest estimate, experts told us.

Filling the gaps in disease burden estimates

By the end of 2020, India officially had 10.3 million laboratory-confirmed cases of COVID-19, the first case having been reported on January 30, 2020, in Kerala. However, the true number of infections--the total number of people who contracted the virus, whether or not they showed symptoms--was likely much higher, according to both national sero-surveys.

While there have been several city-level sero-surveys in which investigators test a sample population for the prevalence of antibodies against COVID-19 in their blood, the only countrywide sero-survey is the one conducted by the Indian Council of Medical Research (ICMR). The first round conducted in 70 districts estimated 6.4 million infections in May-June, 2020. By the second round conducted in August, the estimate was up to 74 million.

The results of the third sero-survey (December-January) currently being conducted are not yet out, but we can expect a smaller increase in the sero-prevalence between August and December than between May-June and August, on account of the slowing of cases observed since mid-September in India, Manoj Murhekar, director of the National Institute of Epidemiology, Chennai, and lead author of the ICMR sero-surveys, told IndiaSpend. That would put the number of estimated COVID-19 infections by the end of 2020 above 75 million at the lowest estimate, an ICMR scientist who is part of the sero-survey project told IndiaSpend, asking not to be named as the survey was under way. This was, he admitted, a conservative estimate.

Estimated total infections being exponentially greater than the number of officially reported cases is not exclusive to the COVID-19 disease, according to a government report. India collates its official statistics on incidence, prevalence and mortality rates of different diseases in the National Health Profile (NHP), published by the health ministry's Central Bureau of Health Intelligence. The government is aware that its officially reported numbers represent an under-estimate, which it attributes to public sector versus private reporting issues. "Since the reported Data is by and large from Government health facilities, it may have limitations in terms of its completeness as Private Medical & Health Care Institution still need to strengthen their reporting to their respective Government Health units (sic)," said the most recent NHP in October 2019.

Further, a whole host of diseases, much like COVID-19, have a strong component of asymptomatic infections that data gathered from hospitals will miss. In 2019, for instance, a national sero-survey for dengue led by Murhekar noted that 75% of dengue infections in India were likely to be "subclinical", meaning asymptomatic and undetected.

That is where the Global Burden of Disease (GBD) project steps in. The GBD is a mammoth global collaboration led by the Institute for Health Metrics and Evaluation in Seattle, USA, that has been using multiple sources to estimate the true burden of disease and death in 195 countries, from 1990 onwards. In India, the GBD project partners with the Public Health Foundation of India (PHFI) to produce national- and state-level estimates of disease and death, and their data aim to also take into account unreported and asymptomatic infections for all diseases, much as a sero-survey would.

"Regarding the GBD estimates, these are based not only on [large and smaller scale] household [health] surveys' self-reported data. An effort is made to use all available data sources including various types of population-based assessments in order to arrive at the best possible overall estimates of diseases," the team behind the Indian estimates told IndiaSpend in an email.

A comparison between officially reported data from the NHP and GBD estimates shows under-counting for both reported infections of and deaths from several diseases.

If the NHP's estimates for disease, then, are comparable to India's officially reported COVID-19 cases, while the GBD numbers are closer to what sero-surveys are showing as the likely number of true COVID-19 infections, where does COVID-19 stand in comparison to other major diseases?

First, a look at official numbers. Ischemic heart disease, cancers and chronic obstructive pulmonary disease are the three top killers of Indians, but for this analysis, only infectious diseases were considered. Among communicable diseases, the broad categories of "acute respiratory infections" and "acute diarrhoeal disease" accounted for the largest share of 'morbidity' or illness in India in 2018 (the most recent year for which data are available), according to NHP 2019. The specific diseases typhoid, tuberculosis, pneumonia and malaria followed. Those numbers show that there were nearly twice as many reported cases of SARS-CoV-2 (the virus that causes COVID-19) in 2020 as of typhoid, tuberculosis, malaria and pneumonia in 2018 put together. There were nearly five times as many cases of SARS-CoV-2 in 2020, as there were officially reported tuberculosis cases in 2018. The official number of deaths from COVID-19 in 2020 also dwarfed the number from other infectious diseases in 2018. However, these are under-estimates of both the true number of infections and of deaths, as previously said.

COVID-19 infections estimated to be higher than most serious communicable diseases

The above, however, are under-estimates of both the true number of infections and of deaths, as previously said. Comparing the GBD 2019, estimates of total communicable disease burdens in India, along with the second countrywide sero-survey-derived numbers for SARS-CoV-2, indicates that there were more COVID-19 infections in India in 2020 than any other single communicable disease in a normal year, except for the broad categories of diarrhoeal diseases and respiratory infections. While upper respiratory infections are the most common communicable disease, they are rarely serious, and hence not comparable. The GBD records fewer than 800 deaths annually from upper respiratory infections in India.

Comparing deaths from COVID-19 with deaths from other communicable diseases could be more complicated. The GBD numbers show that deaths from most communicable diseases are substantially under-counted. India recorded just 85 official deaths from malaria in 2018, while the GBD estimates over 33,000. The GBD estimates of over 632,000 deaths from diarrhoeal disease meanwhile are over 400 times the official estimates. But India does not yet have estimates of the "true" number of COVID-19 deaths, and the official count is likely a substantial underestimate, given evidence of under-counting of COVID-19 deaths. Just the extent of this undercounting is harder to estimate.

When Mumbai made all-cause mortality data from March to July available, it became clear that there was substantial excess mortality, despite likely lockdown-driven reductions in road and rail deaths. Precisely how much of this excess mortality can be attributed to COVID-19 is harder to estimate, mathematician Murad Banaji, who has been studying the pandemic and Mumbai's figures in particular, told IndiaSpend. Moreover, Mumbai is not India. Estimates of COVID-19 undercounts will vary widely by region, making an all-India number hard to extrapolate.

The GBD data show over twice as many deaths in 2019 from drug-susceptible tuberculosis alone than from SARS-CoV-2 this year, and more deaths yet from lower respiratory infections and diarrhoeal disease. However, if the "true" estimate of COVID-19 deaths is substantially higher than the official count--in Mumbai, for instance, excess deaths at 13,058 were 100% higher than its recorded 6,395 COVID-19 deaths between March 1 and July 31, 2020--then COVID-19 could turn out to be the single largest infectious killer-disease in 2020.

Tanu Singhal is an infectious diseases expert and a consultant paediatrician at Kokilaben Dhirubhai Ambani Hospital in Mumbai. In her experience, the prevalence of COVID-19 among adults in 2020 far outstripped that of dengue, malaria, chikungunya, influenza and other such illnesses in previous years put together, she told IndiaSpend. "One in every four or five adults seems to have had COVID-19, and even the sero-prevalence data is indicating that. In past years even during dengue outbreaks, you wouldn't hear of one in every 10 people getting dengue, for instance," she said.

Filling gaps in estimates with anecdotal evidence is complicated. Some doctors like Singhal report having seen more COVID-19 cases in 2020 than any infectious disease in past years. But a doctor's experience depends substantially on the geographic location and socio-economic make-up of the area they serve.

Ultimately, it is only large-scale surveys that can provide the final answers. "We will need good all-cause mortality data at the national level or from a large household survey to be able to properly answer how many deaths were from COVID-19 and how this compares with other diseases," Giridhar R. Babu, epidemiologist with PHFI, told IndiaSpend.

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