Background
- New cases generally declined from April 24 to June 9, after which new cases generally began rising after June 9
- New cases on June 21 reached 26,079 (which was a significant decrease from the preceding 2 days)
- The 7 day average of new cases has increased from 21,265 on June 9 to 27,227 on June 21, an increase of 28%
- The 7 day average of new cases on 6/21 was 27,227, which is 16% less than the highest 7 day average of new cases of 32,425 on April 10
- New deaths have generally been declining since April 21 even as new cases have started to recently increase
- Since the increase in new cases started on June 10, the 7 day average of new deaths has decreased from 982 new deaths on 6/10 to 626 new deaths on 6/21, a decrease of 36.3%
- Deaths are a lag indicator, which means that new deaths are expected to increase after an increase in cases
- In a study reported in Lancet on March 12, WHO reported that the time between symptom onset and death ranged from about 2 weeks to 8 weeks (see: the Lancet here.)
- In another study published in Lancet on March 30, the mean period of time between the start of symptoms and death has been estimated as 17.8 days (see the Lancet here.)
- However, new deaths began declining on April 21, which was 3 days before the peak number of new cases occurred on April 24, which is inconsistent with expectations
Analysis
- While there has been a rough correlation between new cases and new deaths, new deaths have been declining faster than new cases
- New cases decreased by 48.8% between its peak on April 24 and June 9 whereas new deaths decreased by 63.6% between its peak on April 21 and June 9
- From June 9 to June 20, the 7 day average of new cases increased by 28% while the 7 day average of new deaths decreased by more than 36% — that is a non-correlated divergence of 54%
- Although daily numbers of cases and deaths can be volatile, and new cases have unquestionably been trending higher over the last 11 days (notwithstanding the decrease in new cases over the weekend) and new deaths have been trending lower for almost 2 months, including during the recent period during which new cases have been surging.
- A number of explanations have been suggested, including:
- First, perhaps new deaths will increase as a result of the recent spike in new cases. Although we have not seen a corresponding increase in the number of new deaths, perhaps deaths will increase in the near future. We’ll know a lot more in 4 to 6 weeks (if the average number of days between symptom onset and death is around 18 days, then we should start to see some significant spikes in new deaths within the next week or so, but with 18 day being an average, we probably should have already started to see some increases in new deaths).
- Second, we know more about C19 now than we did a few months ago, and perhaps improved treatments are reducing the number of new deaths. This explanation will make more sense if new hospitalizations increase with increases in new cases. There does appear to be increased hospitalizations in some States that are experiencing increases in new cases, but the data is not always available on a timely basis. So, we will monitor a few States to evaluate to what extent hospitalizations increase as new cases increase.
- Third, there may be far more asymptomatic people than we think. The CDC has estimated that up to 35% of infections are asymptomatic. Other has found that 40 to 45% of infections are asymptomatic (see 40–45% who contract new coronavirus are asymptomatic). Another paper estimated that up to 80% of infections are asymptomatic (although high percentages of asymptomatic cases can substantially increase the spread of C19, it also means that a high percentage of people may not be at risk, which could explain the divergence between new cases and new deaths).
- Fourth, some have argued that an increase in new cases AND a decrease in deaths indicates that healthier people are becoming infected as they engage in more activities while vulnerable people are being more cautious. As heathier people are much less likely to die, that is a potential explanation, which also provides a potential path for reopening our economy (e.g., economies are reopened for healthy people with few restrictions and more vulnerable people take additional precautions).
- Fifth, some have suggested that the virus has become less lethal (see next story). While there research and expert opinions to support that theory, most experts appear to believe that is not the case. Although this seems implausible, it would explain some of the inconsistencies in the numbers and trends and it is possible, so we will continue to track.
- At this time, while we concede that the first explanation is plausible, we believe that a combination of the second, third and fourth explanations is a more plausible explanation, but time will tell.