How many injections prevent one covid death?

And how does that compare to harm?

Risk is notoriously difficult to communicate effectively. It is especially hard when referring to an emotive subject like the risk of dying as the emotional response prevents rational interpretation of complex numbers. To simplify understanding of the benefits of interventions the number of people who need to be treated to prevent a covid death can be measured, the number needed to treat (or “NNT”). The same calculation can be applied to vaccination to give a number needed to vaccinate to prevent a covid death.

The data available to carry out such a calculation is flawed, but even if we assume it is perfect the answer we get is alarming.

For the Delta wave the UKHSA published deaths by covid vaccination status. From this the risk of dying if vaccinated or unvaccinated could be calculated as a proportion of the whole vaccinated or unvaccinated population. The vaccinated population can be accurately measured via records of those vaccinated, but the size of the unvaccinated population is by definition only an estimate, and the problems with the figures used have been discussed before. However, we are going to use the UKHSA estimates for the unvaccinated population. If we assume that the covid death rate in the unvaccinated had applied to the vaccinated then the number of covid deaths prevented by vaccination will be evident. Using the number of people vaccinated we can then calculate the number that needed to be vaccinated to prevent each covid death.

Doing this calculation for each age group gives the following results for the duration of the Delta and first Omicron waves. The Delta data is for a period of 16 weeks where Omicron is only for 12 weeks because data was not published thereafter. This in itself is rather irregular. It very much has the appearance that the data is not being published because it does not show what the prevailing narrative insists upon. This lack of transparency is worrying and does not increase public confidence in government statistics.

AgeCovid deaths prevented based on differences in covid death rates per 100kDELTA (27th Aug – 16th Dec 2021)Number needed to vaccinate per covid death prevented based on differences in covid death rates per 100kDELTACovid deaths prevented based on differences in covid death rates per 100kOMICRON(3rd Jan – 27th Mar 2022)Number needed to vaccinate per covid death prevented based on differences in covid death rates per 100kOMICRON
<18-0.9NegativeNegativeNegative
18-29709300021785000
30-392402700050338000
40-4964010000161167000
50-592740260087063000
60-6945801300216030000
70-799100520560017000
80+11900 230 78007300
Total29,27016,662
Table 1:  Covid deaths prevented and number needed to vaccinate to prevent a covid death based on covid death rates from UKHSA data.

When applied to drugs, published data suggest that only half of doctors would prescribe a drug with a number needed to treat of 200. That would imply that half of doctors would not recommend it even for over 80 year olds during the Delta wave. For Omicron the number is in a different league.

If the intervention lasted longer than the Delta wave then the number needed to vaccinate would fall as benefits continued. However, the length of time that the vaccine could be said to have imparted a benefit can surely be no longer than the duration of a wave of covid. It is therefore hard to make that claim. 

Any underestimate of the size of the unvaccinated population (as seems likely) would make the number needed to vaccinate even higher than these figures. Furthermore, the data does not distinguish between people with co-morbidities and those who are healthy. Overall 95% of covid deaths have been in people with pre-existing conditions so the number needed to vaccinate in the healthy population will be far higher still than the numbers given here. 

As well as understanding the number needed to vaccinate in order to prevent a covid death, it is important to also consider the number needed to vaccinate in order to cause a non-fatal harmful event. Data to estimate this is still difficult to come by. However, Phil Harper has carried out this calculation using the Pfizer trial data. For every covid hospitalisation prevented from vaccination there were an additional 1.3 hospitalisations for serious adverse events related to the vaccine. That data was available to regulatory bodies in December 2020. More recently, analysis of trial data as a whole has been published showing the increased risk of serious adverse events was higher than the reduction in risk for covid hospitalisations for both Moderna and Pfizer. 

Because Omicron is milder the ratio between benefit of vaccination and harm from vaccination will have swung even further towards harm. It is becoming harder and harder for medical professionals to claim they are ignorant of these facts. The data is in and the harms outweigh the benefits.

Appendix

The numbers in the table were calculated from UKHSA vaccine surveillance report data in the following way:

  1. The total covid deaths for vaccinated and unvaccinated in each age group over the whole wave were summed. The total covid deaths in the vaccinated were summed regardless of doses given.
  2. For Delta reports for 2021 weeks 35-38, 39-42, 43-46 and 47-50 were used. For Omicron reports for 2022 weeks 1-4, 5-8 and 9-12 were used. 
  3. UKHSA estimates for the number 
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