Dr. Tom Frieden is the former director of the US Centers for Disease Control and Prevention, and former commissioner of the New York City Health Department. He is currently president and CEO of Resolve to Save Lives , a global non-profit initiative funded by Bloomberg Philanthropies, the Chan Zuckerberg Initiative, and the Bill and Melinda Gates Foundation, and part of the global non-profit Vital Strategies . Resolve to Save Lives works with countries to prevent 100 million deaths and to make the world safer from epidemics. Dr. Frieden is also senior fellow for Global Health at the Council on Foreign Relations . The views expressed in this commentary are solely those of the author.

(CNN) There are similarities and differences between Covid-19 and the flu, but we know much less about the novel coronavirus. As we look at what happened in China, and what's happening now in Italy, it's easy to adopt a fatalistic attitude that "there's nothing we can do, we're all going to get it anyway." This could not be further from the truth. Even if half of all people worldwide become infected with Covid-19 -- and we don't know if the infection rate will be nearly that high -- half will not. And of those who do get infected, there's a lot we can learn from flu to increase the likelihood of survival.

Symptoms. Some symptoms of flu and Covid-19 are similar: a dry cough and fever. Covid-19 more often causes shortness of breath and difficulty breathing -- a sign to seek immediate medical attention. Influenza causes aches, fatigue, headache and chills; these appear to be less common with Covid-19. Flu symptoms tend to come on abruptly, getting worse in a day or two. With Covid-19, symptoms may be more gradual and take several days to get worse. If you are sneezing, or have a stuffy or runny nose, the good news is that you probably just have a garden-variety common cold -- ironically, one possibly caused by a different coronavirus.

Covid-19 is more infectious than flu. It appears a person who is infected with Covid-19 spreads it to more people than the flu, so it may spread farther and faster than flu.

Covid-19 is more likely to kill than flu. On average, about 1 in 1,000 people who get flu die from it -- mostly the elderly and people with underlying health conditions, but flu sometimes kills healthy young people and pregnant women. We don't know the precise case fatality ratio for Covid-19 because of incomplete testing of possible cases and insufficient information about outbreaks. But so far, Covid-19 appears much deadlier than seasonal flu, and quite possibly deadlier than the flu pandemics of 1957 and 1968 , each of which killed more than 1 million people around the world. Those pandemics had estimated case fatality ratios far below 1% -- and Covid-19 may kill more than 1 in 100 people who get sick with it. This is not as high as the 1918 flu pandemic , which has been estimated to have killed 2.5 of 100 who it made sick, killing an estimated 675,000 Americans at a time when our population was one-third what it is today. As with the flu, older people and those with serious health conditions such as heart or lung disease, cancer or diabetes are at much higher risk.

And there is a fundamental difference in how flu and Covid-19 kill. Many deaths from flu are caused by secondary bacterial pneumonia and heart attacks that develop after the flu has weakened someone's resistance. With Covid-19, most deaths are caused by acute respiratory distress syndrome (ARDS), which causes already-damaged lungs to fill with fluid, and makes breathing difficult. Unlike pneumonia, there is no pharmaceutical treatment for ARDS. That is why a potential shortage of ventilators is so dangerous: They are the last-ditch supportive treatment for Covid-19 while the body heals itself.

No vaccine. Unlike flu, there is no vaccine for Covid-19 and we are unlikely to have one for at least a year, if ever. The flu vaccine is relatively weak compared with other vaccines -- around 60% protection in a good year when the vaccine is well-matched to circulating strains and 30% or less in a bad year. But at least we have a vaccine for flu. And although it is not highly effective, the flu vaccine helps build herd immunity, which prevents or at least slows disease spread, and often reduces symptom severity.

No treatment. There are not yet any medications that can be used to treat Covid-19, although clinical trials are currently underway and being accelerated. For flu, Tamiflu and other antiviral drugs shorten the duration of illness and reduce symptom severity if started within two days of symptom onset. This is important, even if antivirals are not as effective as antibiotics: Less-severe flu symptoms reduce the need for intensive care and reduce the risk of death.

No immunity. Because Covid-19 is caused by a novel virus, it is likely that there is no natural immunity to it, unlike the flu. In most years, some percentage of the population will be resistant to flu infection and less likely to become severely ill from that year's flu strains because they previously had a similar strain of the flu or were vaccinated against it. That retained immunity can reduce the severity of flu symptoms. During the 2009 H1N1 flu pandemic , people over age 35 generally did not get severe illness because of partial immunity, which may have been from previous infection with a similar strain. During the 1918 flu pandemic, older people appear to have been less likely to become ill and die because of past immunity. With Covid-19, no one has this type of existing immunity as far as we know -- although why kids don't get severely ill is a mystery -- which is why some epidemiologists have predicted that two-thirds of all people in the United States might become infected.

Children at reduced risk. One bit of good news is that, unlike with the flu, children up to at least age 18 appear to not become very ill with Covid-19. They can become infected, but fatal infection appears to be extremely rare. Flu kills about 100 children under age 17 in the US each year (most under age 5). We don't know to what extent children are important in spreading Covid-19. People without symptoms are generally less likely to spread infections, and children are less likely to show symptoms. Because of this, we don't know whether closing schools will substantially reduce spread of this coronavirus.

Covid-19 is more infectious and more deadly than flu. We have fewer tools and no natural immunity. And, we know much less about how to fight it. That's why it's even more important to take protective measures. Wash your hands frequently and thoroughly, avoid touching surfaces to the extent possible, cover your coughs, and stay home if you're feeling ill -- the same recommendations we give to people to avoid getting and spreading the flu. Specifically for Covid-19, actions of universities and workplaces are closing and allowing telecommuting and distance learning make sense. Medically vulnerable people need to keep a safe distance from others. Nursing homes need to do everything possible to prevent Covid-19 from entering their doors -- either by visitors or staff. Large public gatherings need to be cancelled or radically altered; the NCAA and NBA are taking the right steps to limit contact, which will help flatten the epidemic curve and reduce the chance of a sharp spike in cases that could overwhelm health care facilities. Actions that delay cases allow us to better manage our health care resources -- which could be stretched to the breaking point if cases surge dramatically -- and give us more time to develop effective treatments to prevent the worst complications.

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Finally, most people who get flu or Covid-19 do well; 80 or 90% of those infected with the novel virus have mild, moderate or no symptoms. However many people die from it, this will be too many. Although the coronavirus pandemic will certainly get worse before it gets better, it will get better. And even at the worst of the coronavirus pandemic, many people (no one knows what proportion) won't get infected, and, of those who do get infected, 99 out of 100 will recover. So, it's responsible to be proactive now to limit the harms of Covid-19, but it's also good to keep in mind that this, too, will pass.

By taking these actions on both a personal and societal level, we give ourselves the best chance to mitigate the impact of Covid-19. It's too late now to prevent this coronavirus from spreading in our communities, but by working together to limit and slow that spread, we can save lives.