The Absolute Risk Reduction of the Pfizer Biontech Booster Shot

Pfizer Biontech announced that their COVID-19 Vaccine Booster Dose showed a high efficacy rate based on their Phase 3 Trial Data. [1]

The Pfizer Biontech is incomplete because they only stated the Relative Risk. It should also show the Absolute Risk Reduction that applies to an individual.

This article shows that only one person will benefit out of 48 people who will get the Pfizer Biontech booster. This piece will show why that “vaccine effectiveness” is only suitable for five months.

How was the Pfizer study done?

All trial participants previously completed the primary two-dose series of the Pfizer-BioNTech vaccine, and then were randomized 1:1 to receive either a 30-µg booster dose (the same dosage strength as those in the primary series) or placebo.

The whole study group was composed of 10,000 individuals 16 years of age and older. The 10,000 were divided equally into the vaccine group (5,000) and the placebo group (5,000).

The outcome of the Pfizer Biontech Booster Phase 3 Trial Data

During the study period, there were 5 cases of COVID-19 in the booster group, and 109 cases in the non-booster group.

Based on the results, they reported that (emphasis added)

During the study period, there were 5 cases of COVID-19 in the booster group, and 109 cases in the non-boosted group.

The observed relative vaccine efficacy of 95.6% (95% CI: 89.3, 98.6) reflects the reduction in disease occurrence in the boosted group versus the non-boosted group in those without evidence of prior SARS-CoV-2 infection.

What does vaccine efficacy mean?

Vaccine Efficacy is another term for Relative Risk Reduction. RRR is the ratio of attack rates with and without the vaccine. RRR is used in vaccine research to compare results between vaccine trials. It is always used for presentations to the media, stockholders, and physicians because the higher numbers are more impressive.

However, Vaccine Efficacy or RRR does not tell the whole picture and does not apply to patients. There is another measure for people, the Absolute Risk Reduction.

The ARR is the difference between attack rates with and without a vaccine and considers the whole population. ARR tells us about the effectiveness of that vaccine as it relates to an individual.

Below, I will show how to get the ARR. I will use the same guide in Know the Absolute Risk Reduction of the COVID-19 Vaccines! The numbers in the image are examples and do not reflect the current study.

Source: Outcome Reporting Bias in COVID-19 mRNA Vaccine Clinical Trials

How to get the Absolute Risk Reduction

In the Vaccine Group: How many people got sick with COVID-19 after getting the booster shot?

Five cases got sick with COVID-19 in the Experimental group of 5,000.

Experimental Event Rate (EER) 5/5,000 = 0.001 (0.1% risk)

For the Control Group: How many people got sick with COVID-19 after getting the booster shot?

One hundred nine cases got sick with COVID-19 in the Control Group of 5,000.

Control Event Rate (CER) 109/5,000 = 0.0218 (2.18% risk)

Absolute Risk Reduction

The Absolute Risk Reduction (ARR) or Vaccine Risk Reduction is calculated by

CER – EER = ARR

0.0218 – 0.001 = 0.0208 (2.08%).

The Absolute Risk Reduction is 2.08%

Relative Risk Reduction (Vaccine Efficacy)

Relative Risk Reduction (RRR) = Vaccine Risk Reduction relative to Placebo Risk

ARR / CER = RRR

0.0208 / 0.0218 = 0.954 RRR (95.4%). Not the same as the reported 95.6%, but close enough. They used a longer formula.

Numbers Needed to Vaccinate

Numbers Needed to Vaccinate (NNV) is the number of people who need to be vaccinated to benefit one person. Ideally, the NNV should be one. Almost all vaccinated people should be protected if the vaccine effectiveness is 95.6%.

NNV is calculated using the reciprocal of the ARR (1/ARR)

1/ARR = NNV

1/ 0.0208 = 48.

For one person to benefit, 48 people need to be vaccinated with the booster shot.

How long is the protection of the booster shot?

We go back to the stated duration of the study.

Symptomatic COVID-19 occurrence was measured from at least 7 days after booster or placebo, with a median follow-up of 2.5 months.

In statistics, the median means the middle value of the data. That means the patients were followed for five months.

Why only five months? Could it be that based on previous research, the effectiveness of the Pfizer Biontech vaccine decreases at five months? What is the source of that data?

From Pfizer. A study funded by Pfizer and done by its employees was published in The Lancet on October 4, 2021. It reported,

Effectiveness against delta infections at 1 month after being fully vaccinated was high at 93% (85–97) but fell to 53% (39–65) up to 5 months after being fully vaccinated

The same result has been seen in Israel. The preprint study, Waning immunity of the BNT162b2 vaccine: A nationwide study from Israel, reported

These results indicate a strong effect of waning immunity in all age groups after six months.

If the authors extended the booster study for another month, the vaccine effectiveness would likely be lower. The vaccine is the same dose and based on the Wuhan type of SARS-CoV-2 as the first two doses. New variants may even show up shortly that can also decrease the booster’s effectiveness.

ARR and NNV should be reported instead of RRR or Vaccine Efficacy

Reporting Absolute Risk Reduction is not a new concept. ARR and NNT are recommended to be used together to inform physicians and the general public. [3]

In order to inform care, it is recommended that controlled trials with binary outcomes and/or survival data report both relative and absolute effect measures.

Unfortunately, the general public is not made aware of ARR.

Getting the vaccine is a personal decision. All should weigh the risks and benefits.

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Don’t Get Sick!

References:

Pfizer and BioNTech Announce Phase 3 Trial Data Showing High Efficacy of a Booster Dose of Their COVID-19 Vaccine. Businesswire. October 21, 2021
Brown RB. Outcome Reporting Bias in COVID-19 mRNA Vaccine Clinical Trials. Medicina. 2021; 57(3):199. https://doi.org/10.3390/medicina57030199
Elliott, M.H.; Skydel, J.J.; Dhruva, SS; Ross, J.S.; Wallach, J.D. Characteristics and Reporting of Number Needed to Treat, Number Needed to Harm, and Absolute Risk Reduction in Controlled Clinical Trials, 2001–2019. JAMA Intern. Med. 2020, 181. [Google Scholar]
Kahwati, L.; Carmody, D.; Berkman, N.; Sullivan, H.W.; Aikin, K.J.; DeFrank, J. Prescribers’ Knowledge and Skills for Interpreting Research Results: A Systematic Review. J. Contin. Educ. Health Prof. 2017, 37, 129–136. [Google Scholar] [CrossRef]
Goldberg Y, Mandel M, Bar-On YM, Bodenheimer O, Freedman LS, Haas E, et al. Waning immunity of the BNT162b2 vaccine: A nationwide study from Israel. medRxiv. 2021.08.24.21262423. Preprint. https://doi.org/10.1101/2021.08.24.21262423

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How to get the Absolute Risk Reduction

Numbers Needed to Vaccinate

How long is the protection of the booster shot?

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