An epidemiologist’s advice for living with COVID
She chooses to live like she would during bad flu season
IT SEEMS LIKE a pretty simple question: Have we reached the point where COVID-19 has become less lethal than the flu? But if you ask a group of public health/infectious disease experts, it’s almost certain some will say yes and some will say no. In all likelihood, they’re both right, because the question is not nearly as straightforward as it sounds.
There are two main ways to think about how deadly or lethal an infectious disease is. The first is in terms of the infection fatality rate, which is often abbreviated as IFR and refers to what proportion of people who get infected die. To know the IFR of a pathogen at any given moment, you need two pieces of data: how many people have recently been infected and how many people have died as a result of that infection. The IFR is a ratio of the two. Unfortunately, here in the US, we do not have either number.
Because COVID-19 causes mild or asymptomatic infection, thus leading to many undiagnosed cases, and because so much testing is going on in people’s homes and not getting reported to health authorities, we really have no idea how many new infections are happening every day. Incredibly, some estimates put the proportion of cases being officially reported at between 2 and 5 percent of total infections. It’s also unclear what fraction of COVID-19 deaths we are overcounting or undercounting due to limitations in our ability to ascertain the true cause of death without in-depth medical record review.
We do know that in Massachusetts, the only state that reports hospitalization by severity, approximately 70 percent of the reported COVID-19 hospitalizations in recent months have not been receiving treatment for severe COVID-19 infection, indicating a rising rate of “incidental COVID-19 admissions,” a phenomenon that is likely also affecting death counts. On the other hand, we also know that even when COVID-19 is not the direct cause of death, it can be a contributing factor. All of this complexity makes it nearly impossible to measure the true death rate for this virus.
Can we attempt to approximate IFR? In March 2022, analysts from the Financial Times did just that, using the robust data set and methodology of the Office of National Statistics in the United Kingdom to estimate the number of infections (reported and unreported), and the number of deaths (counting all individuals with COVID-19 listed on their death certificate). That’s when they determined that the IFR for COVID-19 in the UK had in fact dipped below that of flu.
We do not have sufficiently granular data here in the US to do a similar estimate, but last week the CDC published an analysis concluding that the in-hospital mortality rate of those patients admitted due to COVID-19 (removing those with “incidental” COVID-19 using pre-set criteria) had dropped substantially from 15.1 percent during the delta period (July to October 2021) to 4.9 percent in the later omicron period (April to June 2022). That’s good news.
The second way to think about death from an infectious disease is in terms of crude mortality rate, or what proportion of a population dies of the infection in question. While the IFR of an infection can fall over time due to immunity (from vaccination and infection), improved medical therapies, and inherent changes in the pathogen (such as what we are seeing with the reduced severity of omicron compared to prior COVID-19 variants), that does not mean that crude mortality always follows, since the latter also depends on how many people are infected in a given period of time.
Indeed, the authors of the Financial Times analysis noted that the crude mortality rate from respiratory illness remained higher than that of a typical flu season despite the dramatic drop in IFR. Today, US authorities are reporting 300-500 deaths per day from COVID-19, putting us on target to see 113,000-188,000 deaths in a year. Flu kills 12,000 to 52,000 annually.
Barring a new variant that is either more immune evasive or that inherently causes more severe disease (which could happen), we can expect IFR to continue to decrease given the growing immunity of the population and new knowledge and development of vaccines and treatments. Crude mortality, however, is likely to rise and fall with the number of cases.
So how do we use this knowledge for both policy and individual risk assessment? It was the crude mortality rate, not the IFR, that led to stay-at-home orders, designed to “flatten the curve” to preserve hospital capacity. Those types of measures cause extreme collateral damage, and are meant to be undertaken only once. The key now is to make sure vaccines, testing, and treatment are optimized and widely available. Because resources are finite, those efforts must be targeted to those at highest risk.
On an individual level, people should realize that their risk of mortality from COVID-19 is on par with or lower than what their risk was from flu, but that their risk of contracting COVID-19 is still higher than their risk of coming down with flu most seasons. I choose to live my life like I would during a bad flu season: I do all of the things that are important to me, clean my hands often, and stay away from sick people. To me, those are permanent changes, because the virus is never going away. The question now is when and how you choose to live with it.
Dr. Shira Doron is an infectious disease physician and hospital epidemiologist at Tufts Medical Center.