Healthcare workers are now seeing unprecedented increases in COVID-19 diagnoses and hospitalizations -- but there hasn't been a congruent rise in mortality rates even as case counts set records.
In fact, the COVID-19 mortality rate in the U.S. has fallen since the start of the pandemic.
That decline has no single, clear explanation, but experts have pointed to a host of contributing factors, including a higher proportion of cases among the young, increased knowledge of how to treat COVID patients, better therapies, and less overcrowding in hospitals.
Younger People Infected
Between June and August, 20- to 29-year-olds had the -- a shift from the start of the pandemic, when it was older adults who saw the highest number of infections. The CDC reported that the median age of infected patients dropped from 46 in May to 38 in August.
Some believe that the shift in infections from old to young is the primary explanation for the drop in mortality. A concluded that the relationship between infection fatality rate and age may be exponential. The researchers found that the age-specific infection fatality rate was extremely low among children and young adults, measuring 0.002% at age 10 and 0.01% at 25. However, the rate progressively increased with age, growing from 0.4% at 55 to around 15% at 85.
"When you compare the fatality rate among people in their 20s and 30s to those in their 70s and 80s, it truly is an order of magnitude difference," said Jeremy Faust, MD, an emergency physician at Brigham and Women's Hospital in Boston. "Small changes in the demographics can make huge differences in mortality."
While other explanations for the decreased mortality rate are compelling -- such as the use of better treatments, like dexamethasone, or proning instead of early invasive ventilation -- Faust told 乌鸦传媒 that the redistribution of cases to younger populations is the only explanation with enough statistical power to explain why death rates have remained low.
Better at Treating COVID-19?
Yet some studies show that mortality has decreased among older patients, too. In a cohort of more than 5,000 hospitalized COVID-19 patients at NYU, researchers found that mortality rates dropped 18 percentage points from the start of the pandemic, falling from 26% in March to 8% in August.
Christopher Petrilli, MD, a hospitalist at NYU Langone and co-author of the study, told 乌鸦传媒 that even after adjusting for age differences, there was a considerable reduction in COVID deaths.
"When we ran our statistical models it was very clear that mortality -- even when you controlled for demographic data, chronic conditions, and even how patients initially presented based on vital signs and laboratory values -- still declined over time, and pretty significantly," Petrilli said.
Lower death rates in older groups raises the question of how much better doctors have gotten at treating COVID-19. Mangala Narasimhan, DO, a critical care specialist from Northwell Health in New York, said that more knowledge about how to care for these patients is a critical reason why the death rates have decreased within her health system.
"We have a standardized approach to these patients now," Narasimhan said. When patients arrive for care, it is easier to decide when to start them on steroids or administer remdesivir, as opposed to the beginning of the pandemic when doctors had to make educated guesses about what treatments might have some benefit.
Early intubation, for example, was a strategy used early in the pandemic for patients who had low oxygen levels. But -- turning patients over onto their stomachs -- seems to play an important role in COVID-19 care.
Dexamethasone was one of the ground-breaking interventions that became more widely used when clinical trial results showed that the steroid slashed deaths by a third in patients on mechanical ventilation, and by a fifth for those on supplemental oxygen.
"But steroids do not explain all of the drops in mortality that we've seen," said Petrilli, the clinician from NYU. Those drops may account for a small percentage of the decrease in deaths. Petrilli added that overburdened hospitals at the start of the pandemic may have contributed to a higher mortality rate.
"I think the biggest factor [in the reduction] is that hospitals are not completely overwhelmed," said Narasimhan, who treated patients in New York when it was the epicenter of the crisis. As hospitals in the Midwest experience overcrowding during a third surge of infections, Narasimhan said she is concerned about how healthcare providers will be able to manage care.
"In March and April, we had the luxury that we were the only ones surging and we could borrow doctors from other parts of the country," she said. "All of that now, is not going to be an option, because everyone is surging, in all parts of the country. There aren't spare people to come help, which is also a worry for us."
More Cases, More Deaths
As cases continue to rise across the country, experts worry that the pandemic will still result in high absolute death tolls among all age groups.
Although age-specific mortality rate for young people is relatively low, they still suffered many excess deaths this year. Faust, the emergency physician from Boston, and colleagues authored a medRxiv preprint study showing that COVID-19 was likely the .
"You certainly want to protect the elderly because they are at such higher risk," Faust said. "But the alternative is not to let the virus roam free among the young, because that's when you see this huge increase in deaths that we didn't expect."
Petrilli said it's correct to say that certain patients are at higher risk than others, including the elderly, those with chronic medical conditions, and pregnant women. "But that doesn't mean that the patients who are not in those categories are at low risk. It just means that they are not at as high of a risk."
Until the majority of the population has access to a vaccine, Petrilli said it's important to continue social distancing and mask-wearing -- for one thing, these measures reduce the viral inoculum that an individual may receive, and thus illnesses may be less severe. "This virus didn't change," Petrilli said, warning that it's still "incredibly contagious," and has a much worse death rate than the flu.
"It's going to be a long road," Petrilli added. "While it's good news that the mortality rate is down, the reason that it is down is because everyone is doing a good job with mask-wearing and distancing. We just need to keep it up."