What Makes COVID-19 Different From the Flu?

Living through the COVID-19 pandemic is hard. TIME’s advice column is here to help. Trying to decide if that dinner party is safe to attend? Fighting through your quarantine fatigue? Our health reporters will consult experts who can help find a safe and practical solution. Send us your pandemic dilemmas at covidquestions@time.com, and we will choose some to answer in a column on TIME.com.

Today, Judy Jones from Missouri asks:

To help understand the differences between COVID-19 and flu, I spoke to a few experts on both diseases, including Andy Pekosz—professor of molecular microbiology and immunology at Johns Hopkins University Bloomberg School of Public Health— who has long warned people about the dangers of influenza. Amid the pandemic, he says that hearing people compare the flu to COVID-19 “borders on making me incredibly angry.”

“We have dealt with patients who are teenagers, we’ve dealt with patients who are healthy adults who have come in with very, very serious disease,” says Pekosz. “Our hospital staff is working like crazy to keep up with the demand of patients that are coming in. It’s all around us, the effects of this disease…there are thousands of sick people every day that are coming into our hospitals. And that doesn’t happen with flu.”

Although outbreaks as recent as the 2009 H1N1 pandemic have claimed hundreds of thousands of lives, it’s been more than a century since the influenza virus truly ravaged humanity; the 1918 influenza pandemic killed an estimated 50 million people globally and 675,000 in the United States. Humans have since built up defenses against the flu: scientists have devised effective vaccines against and treatments, while our bodies have developed natural immunity after being repeatedly exposed to it. While different strains of influenza virus typically spreads each year, immunity from past exposure to other strains, as well as vaccination, can still offer protection. (Still, influenza has hardly been conquered; flu vaccines are only 40% to 60% effective at reducing the risk of illness, and Pekosz warns there’s always a chance that a particularly virulent influenza strain could pose a threat much like SARS-CoV-2, the virus that causes COVID-19, has.)

But compared to our typical seasonal flus, what makes SARS-CoV-2 dangerous is that it’s a brand new virus. When it first started spreading around the world, none of our immune systems had experience with it, and it took scientists time to develop effective tests for it, let alone treatment methods and the vaccines that have just recently begun rolling out. Even months into the pandemic, relatively few people have COVID-19 antibodies—fewer than 10% of people in areas across the U.S. had antibodies as of September, per a CDC study published Nov. 24.

What really sets COVID-19 apart from the seasonal flu is its death toll. So far, the novel coronavirus has killed 1.6 million people worldwide, including more than 300,000 Americans. In fact, COVID-19 has been responsible for between about 7% and 23% of all weekly U.S. deaths since the pandemic began, while the flu hasn’t cracked 4% in the last few years, based on CDC figures:

As you can see in the chart above, the share of U.S. deaths due to COVID-19 has yet to reach the high point set earlier in the pandemic, when scientists and doctors were still scrambling to understand and treat the disease, though it’s getting perilously close as daily cases are far outpacing the initial waves. Thankfully, that understanding has come with time, and we now have treatments like Remdesivir for severe cases, doctors have rethought their approach to treating patients, and one vaccine has been authorized for emergency use in the U.S., with more likely on the way.

Still, as the pandemic worsens, many more people are winding up in the hospital with the coronavirus than typically do with the flu. The CDC provides comparable hospitalization figures for both viruses based on a large surveillance network of vulnerable areas. The first surge in COVID-19-related hospitalizations, in the spring, was roughly equal to the particularly bad 2017-18 flu season, but recent surges have surpassed that by a considerable margin, as you can see in the chart below.

When hospitals become crowded with COVID-19 patients—as well as those sick with other illnesses—that can put major strain on vulnerable and exhausted health care workers and the hospital system more broadly, potentially worsening patient outcomes. “At a certain point, it becomes very difficult to provide the level and quality of care that you want to provide for your patients,” says Dr. Paul Thottingal, national lead for infectious disease for Kaiser Permanente.

Finally, even some people who have “recovered” from their initial bout with COVID-19 are suffering long-term, often debilitating effects that don’t typically present with flu patients. Studies have found that about 10% of COVID-19 patients are thought to develop what’s known as “long COVID,” causing them to suffer symptoms like shortness of breath, fatigue and lost of taste and smell. This can affect even people who were just mildly sick with the disease, and those who are young and otherwise healthy. Since COVID-19 is still so new, scientists still aren’t sure just how long these symptoms could last—or whether they could become permanent.

The best approach, for now, remains following public-health guidance like mask wearing and social distancing—which, thankfully, should help curb the seasonal flu, too. It’s looking increasingly like COVID-19 will one day be just as preventable as the flu, if not more so—but mass vaccination is only just beginning, so we’re in for a few more months of pandemic life. “There is no silver bullet for managing critical [COVID-19] illness,” says Thottingal. “The silver bullet is actually preventing the infection in the first place.”

—With reporting from Chris Wilson