- Basic reproduction number – this is the number of cases, on average, that result from spread of a single infected person. The current best estimate is 2.5, meaning that for every one person infected, he/she will spread it to 2.5 others. The projected range is from as low as 2 to as high as 4. In more densely populated areas, this number would be expected to be higher than in areas with lower population density. If immunity develops following infection, this number would decrease over time to the effective reproduction number, which would be lower. At the present time, there is no data on how masks and social distancing play a role in affecting this number.
- Infection fatality ratio – the number of deaths from infection divided by the number of people with the infection, regardless of whether or not they have symptoms. For age 0-19: 0.003% (so survival rate is 99.997%); for age 20-49: 0.02% (survival rate is 99.98%); for age 50-69: 0.5% (survival rate is 99.5%); and for age >70: 5.4% (survival rate is 94.6%). There is a caveat for the last age range as the CDC states that the data is only likely accurate for those up to age 79, so there are not specific numbers for those 80 and older, and those less than 2 years old carry the highest risk in the pediatric age group, despite being grouped with those up to 19. Also, it is important to remember that certain medical conditions may also affect a person’s risk beyond simply the age-related risk so that he/she may be more vulnerable than statics suggest.
- Percentage of infections that are symptomatic – the current best estimate is 40%, although it may be as low as 10% or as high as 70%.
- Infectiousness of asympomatic individuals – again, this statistic has large variability with 75% being the current best estimate but a range as low as 25% or as high as 100%.
- Percentage of transmission occurring prior to onset of symptoms – it is currently projected that 50% of viral transmission happens before the infected person has symptoms. The range may be as low as 30% or as high as 70%.
The CDC recently provided some updates regarding COVID 19. These numbers address both how transmissible the virus is as well as the severity of infection. Keep in mind that these numbers are estimates, and there’s definitely been quite a discrepancy between computer modeling and actual outcomes in the past, although there is now 6 months of data to base these estimates on that wasn’t available before. That being said, here are the current numbers from the CDC website.
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