What Is The True Coronavirus Case Fatality Rate For Young People?
The Chinese data says 0.2% for ages 0-39 but this may be misleading for a several reasons:
a.) only includes data up to Feb. 11
b.) may be biased upwards, because the overall case fatality rate was higher in the early days of the Wuhan outbreak while hospitals were overwhelmed
c.) may be biased upwards, because cases that had only mild symptoms might never have been reported or tested
d.) may be biased downwards, not counting the higher death rates from people who never got access to a hospital and so never got diagnosed
Using the Johns Hopkins data, which is current up to March 4th, the overall/cumulative case fatality rate in China is 3.4%, and the case fatality rate outside China is 1.8%. This lower number may be more predictive of the current case fatality rate since the case fatality rate inside China has dropped over time, from 17% (in January) to under 2% by Feb. 20th, as more individuals have been tested and hospital resources have been mobilized.
The overall case recovery rate from the Johns Hopkins data is 54% worldwide but only 8% outside China. This may simply indicate recency; according to the WHO, mild cases take 2 weeks to recover and severe cases take 3-6 weeks. Or it may indicate that countries outside China are not following up with confirmed cases.
According to the Chinese data on 72,314 cases of COVID-19 (which gives ages for cases, unlike the global data) only about 10% of cases were in people younger than 30, and only 1% of the deaths among confirmed cases were in people younger than 30. 27% of the cases were in people younger than 40, and 2.5% of the deaths. While reporting of cases of coronavirus can be expected to be biased to more severe cases, there is no systematic reason why cases of similar severity would be more or less likely to be reported based on age, so the 10% case risk seems like a credible estimate.
A sample of 509 cases whose demographic information was reported in the media, including cases from outside China, found that 12% of cases were younger than 30, which is similar to the Chinese figure; the sample included no deaths in patients younger than 30.
South Korea may be our best possible estimate of the true case fatality rate, since it is a developed country with a very extensive testing program of more than 140,000 people to date. It has 6088 cases and 37 deaths, or a 0.6% case fatality rate. In Korea, 35.2% of all cases were in people under 30, and 46.2% under age 40, but there have been no fatalities for people under 30. There was 1 death of a person age 30-39, out of 693 cases in that age range. This suggests that in a country with extensive testing for COVID-19, young people are more likely to contract the disease than the Chinese numbers would suggest, but no more likely to die of it. In fact, Korean case fatality rates across all age groups are lower than the corresponding Chinese case fatality rates.
“At least 11 people have died of the COVID-19 disease in the U.S., all but one of them in Washington state, and most of them from a single nursing home in the Seattle area. The other death occurred in California, just outside Sacramento. The coronavirus has been confirmed in 17 states so far.”, according to a news article on March 5. Since the number of US cases to date is currently 211, this gives a whopping 5% case fatality rate, but this number is likely inaccurate since the US is barely testing at all for COVID-19. We don’t have enough data on US cases to get a believable US-specific case fatality rate by age group, but the pattern of deaths is consistent with the story that the disease is much more deadly for the elderly than for younger people.
Conclusion: the true case fatality rate for Americans under age 40 is likely to be LOWER than the Chinese estimate of 0.2%. The proportion of COVID-19 cases under age 40 is likely to be HIGHER than the Chinese estimate of 27%, perhaps as high as the Korean estimate of 46%.
Written by Sarah Constantin