What is constant is that epidemiological triad of agent, host and environment. The interaction between these three is important in understanding how this disease spreads faster.

It was 1918 when the Liberty Loan Parade was organised in Philadelphia to economically support the soldiers who fought in World War I. It was a gathering that did not have many takers among intellectuals, since the Spanish Flu was already wreaking havoc. The Philadelphia public health director still went ahead with the function. A gathering of over two lakh people was followed by over 47,000 fresh cases of the flu.

The Spanish flu was so severe that 4.4 to 6.1 per cent of the Indian population died, according to the National Bureau of Economic Research, Cambridge. The 1918 pandemic killed around 11-14 million in India.

Cut to 2021 in India. Political rallies, religious gatherings. They tell you how very few learn from history. These events from early 2021 were followed by the second wave of the pandemic in India. Often, comparisons have been drawn between the Spanish flu of 1918, renamed 1918 H1N1 flu, and Covid-19, with many believing that it would follow the same trajectory. While the basic principles of infection spread remain the same, both the pandemics are very different and not comparable.

‘BOTH PANDEMICS CAN’T BE COMPARED’

In spite of the similarities in infection spread and the public health response being very similar, these two pandemics can’t be compared, experts said.

“The third waves of the Spanish flu and Covid-19 19 cannot be compared because these diseases are different in how they spread and the new variants make it difficult for Covid-19 to be compared to any other infectious diseases. But what is constant is that epidemiological triad of agent, host and environment, the interaction between these three is important in understanding how this disease spreads faster. Human behavior is important. It is in the hands of human beings,” said Professor Giridhara Babu, epidemiologist, Public Health Foundation of India.

CAN DERIVE LESSONS FROM THE PAST

Experts, however, said there was a lot to learn from past epidemics and pandemics in responding to future challenges. “Both 1918-20 influenza pandemic and the ongoing Covid-19 pandemic have been caused by respiratory viruses and public health measures taken by authorities are very similar,” said Dr Chandrakant Lahariya, epidemiologist.

“In the flu pandemic of 1918-20, the second wave was the most lethal. That has not been a uniform case in Covid-19 pandemic, and we should thank some of the medical and public health advances of the last century. However, for India, the pandemic seems to have repeated history. The ongoing second wave of Covid-19 has not only been brutal, but harshest pandemic wave witnessed in any part of the world,” Dr Lahariya said.

Experts said that though the third and fourth waves were relatively small in influenza pandemic, there were many reasons why both could not be compared. One of the major reasons is that SARS-CoV-2 has new variants that are more transmissible, showing indications of immune escape and some additional virulence.

“We really don’t know if something like that happened 100 years ago. We need to remember that the virus that caused the pandemic 100 years ago was identified 13 years after the pandemic ended,” said Dr Lahariya.

“Now, with new variants, the SARS-CoV-2 is a lot different in behavior, if not genetically, from ancestral virus first reported from Wuhan in Dec 2019. Therefore, we should not presume anything. Apply the principles of epidemiology, prepare for third, fourth and all the subsequent waves, till the disease becomes endemic,” he further said.

‘MANY UNKNOWNS FOR US TO PREDICT ANYTHING’

Dr Chandrakant Lahariya also said a third wave of Covid-19 could hit India after November.

“There are still many unknowns and the only way to prepare for them is by applying knowledge we have. We know that the susceptible pool is reduced, but epidemiology tells us that there could be third wave anytime around or after November 2021. It also tells that it would be smaller in number of people getting affected (as the pool of susceptible has come down),” he said.

WHAT IS COMMON THEN?

The second wave of the Spanish flu killed those between the age of 30-40. The second wave of coronavirus killed many in the mid-age group. The second waves of both the pandemics were more severe. However, a replication of the third wave is not what experts expect.

The Sanitary Commissioner’s report suggests that the death rate in Bombay during the flu pandemic in the week ending July 6 touched the peak of the pandemic’s first wave, which was below 80 deaths per thousand population. However, the peak in the second wave, in the week ending October 12, shot up to as high as nearly 255 deaths per thousand.

Similarly, with Madras, the peak was below 70 deaths per thousand in the first wave, while it rose to above 200 deaths per thousand in the second wave.

It took another 11 weeks for the third wave to arrive after the peak of the second wave. Also, the third wave was significantly less severe than the previous one. The death rate in Bombay remained below 90 deaths per thousand, even at the peak of the third wave.

SPANISH FLU LASTED 2 YEARS

There were three different waves of the pandemic, starting in March 1918 and subsiding by the summer of 1919. The pandemic peaked in the US during the second wave, in the fall of 1918. This highly fatal second wave was responsible for most of the US deaths. A third wave of illness occurred during the winter and spring of 1919, adding to the pandemic death toll. The third wave of the pandemic subsided during the summer of 1919.

THAT WAS 1918, THIS IS 2021

“A hundred years later, we have better technology, better resources in terms of controlling it, we have a vaccine, all of this makes it easier for us to tackle Covid-19 rather than Spanish flu,” said professor Giridhara Babu.