Over the course of the pandemic the death rate in people diagnosed with COVID-19 (the case-fatality rate) has declined. Unpacking all the reasons this may be the case can help us better understand and fight this disease. A few recent studies shed some light on this question. While there might be some encouraging news here, it highlights that this is still a “novel” virus and we have a lot to learn about the illness it causes.
recent study looking at the case fatality rate in the New York region from
March to August found that the death rate for those admitted to the hospital
dropped from 27% to 3%. They also found many possible reasons for this dramatic
decrease. One is the fact that in March New
York hospitals were overwhelmed with COVID cases. They did not have
enough ICU beds or ventilators, and doctors were crushed beneath the initial
wave of cases of a disease they had no experience with. So simply “flattening
the curve” and reducing pressure on hospitals is one important factor.
encouraging reason for the decline is the steep learning curve of knowing how
to treat those who are seriously ill with COVID. Doctors have learned through
direct experience how to better manage COVID patients, and many interventions
became standard practice between March and August. For example, it is better to
rest patients on their stomach than their back, and it is better to delay
ventilation as long as possible. The discovery that steroids can reduce the
risk of cytokine storm was perhaps a significant improvement. Some patients now
get convalescent plasma, something that obviously could not have happened early
on. Remdesevir was given emergency use authorization, but a recent study by the
WHO found no survival benefit from this drug (or from hydroxychloroquine, a
combination of the anti-HIV drugs lopinavir and ritonavir; and interferon).
still do not have a cure for COVID-19 or a proven effective anti-viral,
management has significantly improved and this has definitely contributed to
survival. However – this is not the only effect, and may not even be the major
study also found that as the pandemic progresses, younger and healthier people
are being infected. They naturally have a higher survival rate, even if they
become sick enough to get admitted to a hospital. It seems from this data, to
put it bluntly, that the first surge of the pandemic in the New York region
killed many vulnerable people, and now there are simply fewer of them alive to
catch and die from the virus. Now we are seeing larger numbers of people
infected, but they are healthier at baseline, so the case fatality rate drops.
This is the not good reason for the drop in deadliness of this pandemic.
side point, some have used the fact that the pandemic tends to kill older
sicker people to minimize the significance of the death toll, as if these are
mostly people who would have died soon anyway. But that is not the case. The
pandemic does not mostly kill people who were already on death’s door (although
certainly that describes some victims). The chronic conditions that make people
vulnerable to dying from COVID, such as hypertension, obesity, or asthma, are
also compatible with years of quality life. Anyone with an elderly parent who
has chronic illnesses but is still a valued and loved member of the family
would bristle at the suggestion that their death is no big deal.
while the case fatality rate is lower, the pandemic has moved on to younger
healthier victims. And keep in mind, the average daily death rate of the
pandemic is still very high in the US, about 700 deaths per day, because new
cases remains high and is increasing as we enter what looks like a third surge.
recent study identifies a different potential reason for the decline in the
case fatality rate – the protective measures being used to reduce spread of the
virus. If, for example, you social distance and wear a mask but still get sick
(it’s possible, because these protections are not perfect, people do not
completely adhere to them, and the virus is very contagious) you will likely
get a lower initial viral load than someone who was hugging someone, without a
mask, who was infected. What the study found was two things – that the initial
viral load correlates with the risk of death, and that as the pandemic
progresses people are presenting with a lower viral load on average. So
protective measures seems to be shifting to lower exposure, so many people do
not contract the virus and those that do will tend to have lower viral loads.
This will tend to generate lots of milder cases, some of which will be
diagnosed and even admitted to hospital but have a lower fatality rate.
study also finds that there is likely a significant effect from earlier
diagnosis. We are doing more testing than in March, which means some people
will be diagnosed at an earlier phase of their illness, be treated earlier, and
have better outcomes. This is a good thing, and is another reason to have
aggressive testing – to prevent spread of the virus, but also to treat people
available studies don’t have the power or rigor (because it’s hard to control
for confounding variables in ecological studies) to determine with precision
the relative contribution of all these factors. But they are all plausible and
well-established phenomena in general, and the evidence does show they are all
playing a role. People are surviving more because our care is improving and we
are diagnosing cases earlier, but also because the pandemic has moved on from
the most vulnerable to healthier victims and our public health measures are not
only preventing new cases but shifting cases toward the milder end of the
spectrum through lower viral loads.
this should make us complacent. The death rate remains high, and even a 3% case
fatality rate makes this a deadly illness.