Massachusetts provides a glimpse of the endemic ending of our pandemic

Last update: Tuesday 9/21/21

As per the opening words of the previous note on this blog, we should expect that our pandemic will fade into a "forever" endemic wherein the number of new infections will remain more or less the same from one month to the next for some indefinite future time frame. Most people still believe that the Delta variant only survives because vaccine holdouts are infecting each other; they believe this because they also believe that there aren't enough Delta breakthrough cases to sustain the virus; and they believe this because data that could be used to estimate the percentage of new infections involving breakthroughs has not been available for most states. However, Massachusetts has been publishing this kind of data on a Webpage since 8/24/21 (perhaps earlier).

Massachusetts is one of our nation's most highly vaccinated states. According to the CDC, on 9/20/21, the percentage of all residents of Massachusetts who were fully vaccinated was 67.3 percent.

The Massachusetts Department of Public Health (DPH) has publishes a Webpage every Tuesday that records the total number of breakthrough cases in the state, breakthroughs being fully vaccinated persons who have been infected. Fur example:

• The breakthrough page for 9/14/21 declared that there had been 27,777 breakthrough cases in Massachusetts as of 9/11/21; 
  
  
• it also reported that there had been 23,858 cases as of 9/4/21, a week earlier; the week-to-week increase therefore = 3,919.

The Massachusetts DPH has long published a covid dashboard that is updated on a daily basis. The spreadsheet that provides that data for the dashboard can be downloaded HERE. The spreadsheet contains data for each previous day. This allows readers to select the total number of infections to date in the state on 9/11/21 and 9/4/21, matching the dates for the data reported on the 9/14/21 breakthrough page. 

• On 9/17/21, the spreadsheet recorded 720,245 cases to date as of 9/4/21, 
• and 731,987 cases to date as of 9/11/21; therefore the increase in the total number of infections from one week to the next = 11,742.

Combining the two increases, we see that breakthrough infections accounted for 3,919 / 11,742 = 33 percent of the total new infections. 

Useful undercounts

Contrary to the judgements of numerous public health experts the breakthrough 33 percent share of total new infections was not "small" because the breakthroughs in Massachusetts were not "rare". But how reliable was this calculation?

Ideally, one would calculate the breakthrough share of new cases by determining the total number of new cases (T), determining the total number of new breakthrough cases (B), then dividing B / T. Unfortunately, the only way to make exact determinations of T or B would be to test everyone in the state every week ... which didn't happen and won't happen. The values that the Massachusetts DPH used for T and B were based on the positive results that came from the people who were actually tested. Let's call the number of new infection tests TTest, and call the number of new vaccinated persons who test positive BTest. So who would probably get tested?

• Persons who developed moderate to severe symptoms would probably volunteer to be tested; but persons who were asymptomatic or only had mild symptoms probably would not volunteer to be tested. 
  
  
• Persons for whom weekly tests were mandatory would be tested, e.g., students at some colleges, employees of some government agencies, staff at some hospitals and other medical facilities, prison inmates, employees of some restaurants and other costumer facing businesses, etc.

If Massachusetts only tested these two groups, its estimates for both T and B would be wildly inaccurate. Fortunately, Massachusetts greatly expanded the scope of its testing by including persons identified via its extensive contact tracing programs. Contract tracing thereby made the test estimates more credible. 

Unfortunately, the estimated values BTest and TTest probably underestimated the true values B and T because of mild or asymptomatic cases that were not caught up in the contact tracing nets.

We conclude with a paraphrase of our introduction to the previous note on this blog. Our 18 month pandemic is likely to fade into a "forever" endemic. The endemic will be self-sustaining; like seasonal flu it won't require boosts from travelers returning from countries having higher rates of infection. New infections will occur (1) among unvaccinated holdouts and (2) as breakthrough infections. Most importantly, the percentage of breakthrough infections will not be "small"; it will represent a substantial share of all new infections

Note: This analysis will be expanded in the near future to calculate the breakthrough percentage of all new infections for each week the Massachusetts Department of Public posted data -- 8/24, 8/31, 9/4, 9/11, 9/18, etc, etc, etc

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Related notes on this blog:

• "Protecting ourselves as our 18 month pandemic fades into a "forever" endemic" -- Last update: 9/17/21