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Coronavirus death rate lower than estimates: Study

Hindustan Times, New Delhi | By
Apr 02, 2020 08:49 AM IST

The death rates varied substantially with age, ranging from a low 0.0016% for people up to none years old to 7.8% for people aged 80 and above.

A new analysis of data from at least 70,000 lab-confirmed cases of coronavirus disease (Covid-19) from China puts the death rate at 1.38%, lower than earlier estimates ranging between 2% and 8% but higher than previous pandemics such as H1N1 influenza, which killed around 0.02% of the people infected in 2009-10.

The study, published in The Lancet Infectious Diseases journal on Monday, warned that 50% to 80% of the global population could get infected with Covid-19, and without interventions such as lockdowns and social distancing, the number of sick people needing hospital treatment could overwhelm even the most advanced health care systems. It, however, said that outcomes may change as the pandemic unfolds and evolves, which would result in the data being revised.

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According to the study, by UK researchers from Imperial College London, Queen Mary University, London, and the University of Oxford, the death rates from confirmed Covid-19 cases came to 1.38%, and the overall death rate to 0.66% after adjusting for undiagnosed cases and population size (not included in earlier studies), according to the analysis of data from 70,117 laboratory-confirmed and clinically diagnosed cases in mainland China, combined with 689 positive cases among people evacuated from Wuhan on repatriation flights.

The death rates varied substantially with age, ranging from a low 0.0016% for people up to none years old to 7.8% for people aged 80 and above. Previous studies have estimated the death rates in people over the age of 80 years to be between 8% and 36%.

While previous estimates of deaths from confirmed cases of Covid-19 ranged from 2% to 8%, deaths from overall infections were estimated to be between 0.2% and 1.6%. Since the past estimates were not adjusted for the fact that only people with more severe symptoms are likely to be tested, and the people in quarantine following repatriation to other countries, the numbers did not reflect the true number of cases across populations, some experts said.

“Estimated death rates of Covid-19 will vary based on how many infected people are entered into the denominator while deaths are in the numerator. While deaths are easier to verify and attribute, the number of infected cases will vary according to the numbers tested with virus specific tests or identified on clinical criteria. Even if these are very liberally applied, we still may not define the denominator precisely as asymptomatic or very mild cases may escape detection by either criterion,” said Dr Srinath K Reddy, president, Public Health Foundation of India.

“The larger the denominator, the greater likelihood of including more mild cases and hence lower the mortality rate. In the initial stages of the epidemic, tests were restricted and diagnostic criteria were narrow, yielding higher mortality rates. Now the denominator is expanding with more inclusive testing and diagnostic criteria, which is showing lower mortality rates that are closer to truth,” said Dr Reddy.

Death on average occurred on average 17.8 days after getting infected, and hospital discharge happened after 24·7 days, the study found. The proportion of deaths from both diagnosed cases and from milder, unconfirmed cases was strongly influenced by age.

The study said that one in hundred people under 30 years of age infected with Covid-19 were likely to need hospitalisation, compared with close to 20 in hundred people who are 80 or above, with both hospitalisation and deaths increasing sharply with age.

It further said that around 11.8% of infected people in their 60s, 16.6% of people in their 70s, and 18.4% of those above 80 developed symptoms severe enough for hospitalisation.

“Our estimates can be applied to any country to inform decisions around the best containment policies for Covid-19,” said Professor Azra Ghani from Imperial College in a statement. “There might be outlying cases that get a lot of media attention, but our analysis very clearly shows that at aged 50 and over, hospitalisation is much more likely than in those under 50, and a greater proportion of cases are likely to be fatal.”

Hospitalisation rates nearly doubled from 4.3% in 40-49-year-olds to 8.2% in 50-59-year olds, and were a low 0.04% for 10 to 19-year-olds, 1 % for people in their 20s, and 3.4% for people aged 30 to 39.

“Retrospective modelling of data from China and Korea helps to identify the interventions needed to stop transmission and treat the severely ill in countries where mass testing is not being done. With many mild cases not even being tested, there is a danger of governments underestimating the nature of the pandemic, much to their peril,” said Dr Dileep Mavalankar, director, Indian Institute of Public Health, Gandhinagar.

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