US President Donald Trump, initially dismissive about the deadly potential of the coronavirus in its early stages in the US, later declared “war” against the “invisible enemy” after a study estimated that more than two million Americans could die if they don’t proceed with caution.

While it’s unclear how much damage Trump’s late acceptance may have done, the president is accurate in describing it as an invisible enemy. 

Many experts and top officials around the world initially focused on those with clear symptoms of the virus. 

But later studies have shown that people having pre-symptomatic or asymptomatic cases, which are more difficult to detect, have spread Covid-19 - potentially as much as patients with visible symptoms from the virus.

"Asymptomatic and mildly symptomatic transmission are a major factor in transmission for Covid-19. They're going to be the drivers of spread in the community," said William Schaffner, a professor at the School of Medicine at Vanderbilt University, who has long advised the Centers for Disease Control (CDC), Washington’s top health agency. 

“The percentage of infected people, even if asymptomatic, in the population is very high. The isolation of asymptomatics is essential to be able to control the spread of the virus and the severity of the disease,” Sergio Romagnani, professor of clinical immunology at the University of Florence, wrote in a letter to officials in Italy, the second worst-hit country after China, where the pandemic killed thousands. 

What makes coronavirus more dangerous is its invisible character in its carriers. Unlike SARS and some previous epidemics, the coronavirus is able to spread to others from presymptomatic people, who seem to be healthier and pass the infection unknowingly. This could be one of the reasons it has been so hard to stop it turning into a pandemic.

What makes coronavirus more dangerous is its invisible character in its carriers. Unlike SARS and some previous epidemics, the coronavirus can spread to others from presymptomatic people, who seem to be healthier and pass the infection unknowingly. This could be one of the reasons it has been so hard to stop it turning into a pandemic.

But the underlying effects of the asymptomatic cases have been underestimated by many countries as the pandemic has travelled across the globe leaving thousands dead in its wake. 

Earlier this month, like Trump’s generally dismissive attitude, the US Health Secretary Alex Azar also appeared to care little about the possible power of asymptomatic cases saying that they are “not the major driver”.  

"You really need to just focus on the individuals that are symptomatic," Azad said, indicating that they will just try to contain symptomatic cases. 

Despite their dismissive rhetoric, the outbreak is killing hundreds every day in different countries including the US as various scientific studies show that the asymptomatic cases could be a key to stopping the spread of the disease. 

According to recent Dutch-led research, the proportion of pre-symptomatic transmission was at significant levels for some countries, 48 percent for Singapore and 62 percent for Tianjin, China. 

A Japanese study also found that nearly 20 percent of the passengers of the Diamond Princess cruise ship with no symptoms tested positive for the coronavirus. 

This week another scientific study from Germany has surfaced, confirming previous studies about the importance of asymptomatic carriers. 

Sandra Ciesek, director of the Institute of Medical Virology in Frankfurt tested passengers coming to the country from Israel. One-sixth of the passengers with no symptoms tested positive. 

Furthermore, the study has revealed some more troubling aspects of the virus. In some asymptomatic patients, the level of viral presence was higher than patients with clear symptoms, indicating that asymptomatic carriers could be even more dangerous than symptomatic people when it comes to spreading the virus. 

About two weeks ago, Bill Gates, the co-founder of Microsoft and the chairman of the Bill and Melinda Foundation, one of the groups contributing to fighting the pandemic, was vocal on the dangerous aspect of asymptomatics. 

"There is also strong evidence that it can be transmitted by people who are just mildly ill or even presymptomatic. That means Covid-19 will be much harder to contain than the Middle East respiratory syndrome or severe acute respiratory syndrome (SARS), which were spread much less efficiently and only by symptomatic people," Gates wrote in an article.  

The US and other countries have begun to recognise the importance of detecting asymptomatic cases. 

In a press conference on the weekend, Deborah Prix, the White House coronavirus coordinator, appeared to question the administration's previous dismissive stance regarding the asymptomatics. 

"Are they a group that are potentially asymptomatic and spreading the virus?" she openly asked in the briefing. 

"Until you really understand how many people are asymptomatic and asymptomatically passing the virus on, we think it's better for the entire American public to know that the risk of serious illness may be low, but they could be potentially spreading the virus to others,” Prix told reporters, indicating a noticeable change of the tone in Washington. 

But beyond recognising the importance of asymptomatics, there is another serious problem: how can you determine unknown asymptomatic cases?

The obvious question is testing. First, one would have to convince millions of seemingly healthy people to get tested in the first place. Further, do countries have enough capacity to test millions of its citizens that show no symptoms? 

Even the world’s most powerful country seems overwhelmed when it comes to finding a solution. 

“The system is not really geared to what we need right now. That is a failing. It is a failing. Let’s admit it,” said Dr Anthony Fauci, the Washington's top doctor responsible for dealing with the pandemic, during a testimony to the American Congress last week.