Age Analysis

Massachusetts Age Analysis Update December 19, 2020

This is an update to the post in early November that looked at cases and deaths by age cohort over time. As I noted in that post, because of the shortcomings of the data supplied by the state, I developed a methodology to estimate this information from the Massachusetts Weekly Public Health Report. The issues with the data and the methodology are explained in (

Since the November post, there have been sharp increases in both cases and deaths in the state. Figure 1 shows the case incidence rate by age cohort.


For all age cohorts, case incidence rates have increased significantly since their summer lows, with particularly sharp increases starting in mid-October through and after Thanksgiving. As of December 19th, case incidence rates for the two cohorts under 60 are now almost at the levels of the 80 and over cohort from early May – roughly 1/2 of 1 percent of all people in those age groups in Massachusetts have been diagnosed with Covid each week over the past several weeks . The rates for the two older cohorts remain lower, but aren’t far behind, and have increased at even a faster rate since the update six weeks ago. Of course, there is significantly more testing now than there was in early May, so it is possible that fewer people are actually infectious now than in May.

Figure 2 shows the percentages of cases by age cohort.

As has been the case since early May, more cases are in the under 40 group. However, the under 40 share of cases, which peaked at somewhat over 60% near the end of September, has declined to about 50%, approximately the same as the under 40 share of the state population. In fact, the case percentages for each age cohort are now roughly in line with their population percentages – the 40 to 59 year old group has a slightly higher case share than population share, and the 60 to 79 year old cohort has a slightly lower case share than population share, but neither discrepancy is particularly pronounced.

This is not the case with deaths, as older adults continue to die at a much higher rate than younger people. Figure 3 shows the death incidence rates by age cohort.

After the summer lull, death rates began creeping up in late October, and the increase has been even more pronounced in the past several weeks. As has been the case throughout the pandemic, those 80 and over are dying with Covid at the highest rates by far – and their death rate is almost ten times greater than that of the 60 to 79 cohort. Death rates remain quite low for those under 60, but have ticked up slightly along with the increase in deaths overall .

The percentage of deaths by age cohort has been remarkably stable throughout the pandemic, as Figure 4 shows – roughly 60% of deaths are for those 80 and over, and over 90% of deaths are for those 60 and over. Very few people under 40 have died from Covid in Massachusetts.

Leave a Reply