Study analysis · The New England Journal of Medicine · 2020
The 95% number that defined a pandemic: What did the Pfizer-BioNTech vaccine trial really show?
In a huge randomized trial, the Pfizer-BioNTech Covid-19 vaccine reduced the relative risk of getting Covid-19 by 95%, which meant about 7 fewer cases per 1,000 people over about 2 months.
Overview
What the study found
The study in plain English — the bottom line, every takeaway we extracted, and what to do with them.
In simple terms
This study is like a fair test where people were randomly split into two groups: one got the real vaccine, the other got a fake shot. Because the groups were otherwise similar, we can be confident that the vaccine itself caused the reduction in Covid-19 cases. But it only looked at short-term results and didn't test everything, like whether it stops people from spreading the virus.
What’s the bottom line?
Researchers tested the BNT162b2 Covid-19 vaccine in a large randomized trial. People were assigned by chance to get the vaccine or a placebo. The vaccine was 95% effective at reducing relative risk of getting Covid-19. In absolute terms, far fewer vaccinated people got Covid-19 than placebo recipients. Side effects were mostly short-term and mild to moderate.
How strong is this study?
The study was very well done because it was large and randomized, which is the best way to compare two treatments. However, we only have the summary, not the full details, and it only followed people for about two months, so we can't be sure about long-term effects or rare side effects.
0 / 100
- COI disclosureconflicts of interest not disclosed
- Data availabilitydata not shared
- Code availabilitycode not shared
93 / 100
- Randomization+20/20
- Blinding+9/15
- Control group+15/15
- Sample size (n=43548)+20/20
- Follow-up+10/10
100 / 100
77 / 100
- P-valuesno p-values reported
- Effect size+20/20
- Confidence intervals+15/15
- Pre-registration+15/15
Each component is scored out of 100 and then capped by the study design — a case series cannot reach the ceiling a randomised trial can, however well it is reported.
Where it sits
RCT reviewsReviews of RCTs (Meta-analyses)
Max 100Randomized TrialsRandomized Trials
Max 90Reviews of Cohort StudiesReviews of Cohort Studies
Max 85Cohort StudiesCohort Studies
Max 72Reviews of Case-Control StudiesReviews of Case-Control Studies
Max 63Case-Control StudiesCase-Control Studies
Max 58Cross-Sectional & Case SeriesCross-Sectional & Case Series
Max 50Expert OpinionExpert Opinion
Max 572 / 100
Probability of being correct
Participants are randomly assigned to treatment or control groups, minimizing bias. The gold standard for testing whether an intervention causes an effect.
This design can establish causation. The study is a randomized, placebo-controlled, observer-blinded trial, which supports causal inference for the primary efficacy endpoint (prevention of laboratory-confirmed Covid-19). However, limitations include observer-blinding only, short median follow-up of 2 months, and abstract-only review, so causal claims should be restricted to the specific endpoint and population studied.
Major COI
Major conflicts that significantly reduce study credibility
The study was funded by BioNTech and Pfizer, the manufacturers of the vaccine being tested, indicating a major conflict of interest due to industry sponsorship.
Funders
Conflict Details
BioNTech and Pfizer: Funded the study (sponsor)
The study is a pivotal efficacy trial for the BNT162b2 vaccine, funded by its manufacturers. No conflict of interest or author affiliation disclosures are included in the provided text, so author employment by the funders cannot be confirmed from this excerpt. The funders' role in study design, data analysis, or publication decisions is not described. The trial is registered (NCT04368728).
Key takeaways
- 01
The vaccine had a 95% relative risk reduction for laboratory-confirmed Covid-19 (95% credible interval 90.3 to 97.6).
- 02
Absolute: 8 of 21,720 vaccine recipients got Covid-19 versus 162 of 21,728 placebo recipients, about 7 fewer cases per 1,000 people over median 2 months.
- 03
Among 10 severe Covid-19 cases after the first dose, 9 were in the placebo group and 1 in the vaccine group.
- 04
Side effects: short-term, mild-to-moderate injection-site pain, fatigue, headache; serious adverse events were low and similar between groups.
- 05
In a group of 1,000 people followed for about 2 months, roughly 7 people who would have gotten Covid-19 without the vaccine were protected.
- 06
The study did not report longer-term safety or efficacy beyond a median of 2 months.
- 07
The absolute risk reduction was about 7 fewer cases per 1,000 people over that period.
Practical takeaways
If eligible, consider getting vaccinated against Covid-19 after discussing with a healthcare provider.
Based on abstract only; full methodology not available. Median follow-up was 2 months, and corrections/errata exist. Long-term safety and efficacy not assessed in abstract.
low confidenceWhen you hear '95% effective,' ask whether that's relative or absolute risk reduction and what the absolute numbers are.
Absolute risk reduction depends on baseline risk and time frame, which vary by population and setting.
low confidenceWhy this study matters
95% relative risk reduction — but what does that actually mean?
In the trial, 8 of 21,720 vaccine recipients got Covid-19 versus 162 of 21,728 placebo recipients. That's a 95% relative risk reduction (95% credible interval 90.3 to 97.6). In absolute terms, it was about 7 fewer cases per 1,000 people over a median follow-up of 2 months.
People hear '95% effective' and often think it means a 95% chance of not getting Covid-19. It's a relative reduction, and the absolute benefit depends on your baseline risk and time frame.
Severe Covid-19 nearly absent in vaccinated group
Among 10 cases of severe Covid-19 with onset after the first dose, 9 occurred in placebo recipients and 1 in a vaccine recipient. This suggests early protection against severe disease, though the numbers are small.
Preventing severe disease is what keeps hospitals from being overwhelmed and saves lives. Even a small number of severe cases in the placebo group highlights the potential impact.
Consistent efficacy across subgroups
Vaccine efficacy was generally 90% to 100% across subgroups defined by age, sex, race, ethnicity, baseline body-mass index, and presence of coexisting conditions. This suggests the vaccine worked broadly across diverse populations.
It's important to know if a vaccine works for everyone, not just a narrow group. This finding helped build confidence for widespread use.
Safety: short-term, mild-to-moderate side effects
The safety profile was characterized by short-term, mild-to-moderate injection-site pain, fatigue, and headache. Serious adverse events were low and similar between vaccine and placebo groups. Safety over a median of 2 months was similar to that of other viral vaccines.
Side effects are a major concern for many people. Knowing what to expect can reduce anxiety and improve informed decision-making.
Corrections and limited follow-up: important caveats
The study has published corrections/errata; readers should check correction notices for updated information. Safety data were limited to a median of 2 months, and longer-term safety was not assessed in the abstract.
Science is self-correcting, and transparency about limitations and corrections builds trust. It also reminds us that initial findings may evolve.
Want the whole report?
Detailed mode opens the full scientific breakdown — every score component, the methodology, conflicts of interest, the evidence analysis behind each claim, and the raw study data.
Overview
What the study found
The study in plain English — the bottom line, every takeaway we extracted, and what to do with them.
Not medical advice. For informational purposes only. Always consult a healthcare professional. Terms
Researchers tested the BNT162b2 Covid-19 vaccine in a large randomized trial. People were assigned by chance to get the vaccine or a placebo. The vaccine was 95% effective at reducing relative risk of getting Covid-19. In absolute terms, far fewer vaccinated people got Covid-19 than placebo recipients. Side effects were mostly short-term and mild to moderate.
Research results
The vaccine had a 95% relative risk reduction for laboratory-confirmed Covid-19 (95% credible interval 90.3 to 97.6). Absolute: 8 of 21,720 vaccine recipients got Covid-19 versus 162 of 21,728 placebo recipients, about 7 fewer cases per 1,000 people over median 2 months. Among 10 severe Covid-19 cases after the first dose, 9 were in the placebo group and 1 in the vaccine group. Side effects: short-term, mild-to-moderate injection-site pain, fatigue, headache; serious adverse events were low and similar between groups.
What this means - more context
In a group of 1,000 people followed for about 2 months, roughly 7 people who would have gotten Covid-19 without the vaccine were protected. The study did not report longer-term safety or efficacy beyond a median of 2 months. The absolute risk reduction was about 7 fewer cases per 1,000 people over that period.
To evaluate the efficacy and safety of the BNT162b2 mRNA Covid-19 vaccine against laboratory-confirmed Covid-19 in persons 16 years of age or older.
In this randomized, placebo-controlled, observer-blinded trial, BNT162b2 conferred a 95% relative risk reduction against laboratory-confirmed Covid-19. In absolute terms, 8 cases occurred among 21,720 vaccine recipients versus 162 cases among 21,728 placebo recipients, or about 7 fewer cases per 1,000 people over a median follow-up of 2 months. Similar relative efficacy (generally 90% to 100%) was observed across subgroups. Safety was characterized by short-term, mild-to-moderate injection-site pain, fatigue, and headache; serious adverse events were low and similar between groups. Note: This study has published corrections/errata; readers should check correction notices for updated information.
Methods Used
Multinational, placebo-controlled, observer-blinded, pivotal efficacy trial. Persons 16 years of age or older were randomly assigned in a 1:1 ratio to receive two doses, 21 days apart, of either placebo or BNT162b2 (30 μg per dose). Primary endpoints were efficacy against laboratory-confirmed Covid-19 and safety. Methodology details not available in abstract.
Main Finding
BNT162b2 conferred a 95% relative risk reduction against laboratory-confirmed Covid-19 (95% credible interval, 90.3 to 97.6). Absolute: 8 cases among 21,720 vaccine recipients versus 162 cases among 21,728 placebo recipients, about 7 fewer cases per 1,000 people over median 2 months. Among 10 cases of severe Covid-19 with onset after the first dose, 9 occurred in placebo recipients and 1 in a vaccine recipient. Safety profile was short-term, mild-to-moderate injection-site pain, fatigue, and headache; serious adverse events were low and similar between groups.
Confidence Level
Limited - based on abstract only, full methodology not available
Study Flags
Red Flags
- •Full text not available - methodology details cannot be verified
- •Published corrections/errata exist; check correction notices for updated information
- •Safety data limited to median 2 months; longer-term safety not assessed in abstract
Practical Takeaways
If eligible, consider getting vaccinated against Covid-19 after discussing with a healthcare provider.
RCT reviewsReviews of RCTs (Meta-analyses)
Max 100Randomized TrialsRandomized Trials
Max 90Reviews of Cohort StudiesReviews of Cohort Studies
Max 85Cohort StudiesCohort Studies
Max 72Reviews of Case-Control StudiesReviews of Case-Control Studies
Max 63Case-Control StudiesCase-Control Studies
Max 58Cross-Sectional & Case SeriesCross-Sectional & Case Series
Max 50Expert OpinionExpert Opinion
Max 572 / 100
Probability of being correct
Participants are randomly assigned to treatment or control groups, minimizing bias. The gold standard for testing whether an intervention causes an effect.
Human RCT
Subject
High probability
on the GRADE evidence scale
This study is like a fair test where people were randomly split into two groups: one got the real vaccine, the other got a fake shot. Because the groups were otherwise similar, we can be confident that the vaccine itself caused the reduction in Covid-19 cases. But it only looked at short-term results and didn't test everything, like whether it stops people from spreading the virus.
Major conflicts — industry funding with significant control over the research. Reporting score and overall score cap have been reduced.
Strengths
- Randomized, placebo-controlled, observer-blinded design
- Large sample size (43,548 randomized)
- Primary endpoint of laboratory-confirmed Covid-19
Weaknesses
- Full methodology not available - based on abstract only
- Observer-blinded only, not double-blind
- Short median follow-up of 2 months for safety and durability
Methodology
Evidence Keywords
Statistical Reporting
Not medical advice. For informational purposes only. Always consult a healthcare professional. Terms
Researchers tested the BNT162b2 Covid-19 vaccine in a large randomized trial. People were assigned by chance to get the vaccine or a placebo. The vaccine was 95% effective at reducing relative risk of getting Covid-19. In absolute terms, far fewer vaccinated people got Covid-19 than placebo recipients. Side effects were mostly short-term and mild to moderate.
Research results
The vaccine had a 95% relative risk reduction for laboratory-confirmed Covid-19 (95% credible interval 90.3 to 97.6). Absolute: 8 of 21,720 vaccine recipients got Covid-19 versus 162 of 21,728 placebo recipients, about 7 fewer cases per 1,000 people over median 2 months. Among 10 severe Covid-19 cases after the first dose, 9 were in the placebo group and 1 in the vaccine group. Side effects: short-term, mild-to-moderate injection-site pain, fatigue, headache; serious adverse events were low and similar between groups.
What this means - more context
In a group of 1,000 people followed for about 2 months, roughly 7 people who would have gotten Covid-19 without the vaccine were protected. The study did not report longer-term safety or efficacy beyond a median of 2 months. The absolute risk reduction was about 7 fewer cases per 1,000 people over that period.
To evaluate the efficacy and safety of the BNT162b2 mRNA Covid-19 vaccine against laboratory-confirmed Covid-19 in persons 16 years of age or older.
In this randomized, placebo-controlled, observer-blinded trial, BNT162b2 conferred a 95% relative risk reduction against laboratory-confirmed Covid-19. In absolute terms, 8 cases occurred among 21,720 vaccine recipients versus 162 cases among 21,728 placebo recipients, or about 7 fewer cases per 1,000 people over a median follow-up of 2 months. Similar relative efficacy (generally 90% to 100%) was observed across subgroups. Safety was characterized by short-term, mild-to-moderate injection-site pain, fatigue, and headache; serious adverse events were low and similar between groups. Note: This study has published corrections/errata; readers should check correction notices for updated information.
Methods Used
Multinational, placebo-controlled, observer-blinded, pivotal efficacy trial. Persons 16 years of age or older were randomly assigned in a 1:1 ratio to receive two doses, 21 days apart, of either placebo or BNT162b2 (30 μg per dose). Primary endpoints were efficacy against laboratory-confirmed Covid-19 and safety. Methodology details not available in abstract.
Main Finding
BNT162b2 conferred a 95% relative risk reduction against laboratory-confirmed Covid-19 (95% credible interval, 90.3 to 97.6). Absolute: 8 cases among 21,720 vaccine recipients versus 162 cases among 21,728 placebo recipients, about 7 fewer cases per 1,000 people over median 2 months. Among 10 cases of severe Covid-19 with onset after the first dose, 9 occurred in placebo recipients and 1 in a vaccine recipient. Safety profile was short-term, mild-to-moderate injection-site pain, fatigue, and headache; serious adverse events were low and similar between groups.
Confidence Level
Limited - based on abstract only, full methodology not available
Study Flags
Red Flags
- •Full text not available - methodology details cannot be verified
- •Published corrections/errata exist; check correction notices for updated information
- •Safety data limited to median 2 months; longer-term safety not assessed in abstract
Practical Takeaways
If eligible, consider getting vaccinated against Covid-19 after discussing with a healthcare provider.
RCT reviewsReviews of RCTs (Meta-analyses)
Max 100Randomized TrialsRandomized Trials
Max 90Reviews of Cohort StudiesReviews of Cohort Studies
Max 85Cohort StudiesCohort Studies
Max 72Reviews of Case-Control StudiesReviews of Case-Control Studies
Max 63Case-Control StudiesCase-Control Studies
Max 58Cross-Sectional & Case SeriesCross-Sectional & Case Series
Max 50Expert OpinionExpert Opinion
Max 572 / 100
Probability of being correct
Participants are randomly assigned to treatment or control groups, minimizing bias. The gold standard for testing whether an intervention causes an effect.
Human RCT
Subject
High probability
on the GRADE evidence scale
This study is like a fair test where people were randomly split into two groups: one got the real vaccine, the other got a fake shot. Because the groups were otherwise similar, we can be confident that the vaccine itself caused the reduction in Covid-19 cases. But it only looked at short-term results and didn't test everything, like whether it stops people from spreading the virus.
Major conflicts — industry funding with significant control over the research. Reporting score and overall score cap have been reduced.
Strengths
- Randomized, placebo-controlled, observer-blinded design
- Large sample size (43,548 randomized)
- Primary endpoint of laboratory-confirmed Covid-19
Weaknesses
- Full methodology not available - based on abstract only
- Observer-blinded only, not double-blind
- Short median follow-up of 2 months for safety and durability
Methodology
Evidence Keywords
Statistical Reporting
Scoring
How strong is this study?
The study was very well done because it was large and randomized, which is the best way to compare two treatments. However, we only have the summary, not the full details, and it only followed people for about two months, so we can't be sure about long-term effects or rare side effects.
0 / 100
- COI disclosureconflicts of interest not disclosed
- Data availabilitydata not shared
- Code availabilitycode not shared
93 / 100
- Randomization+20/20
- Blinding+9/15
- Control group+15/15
- Sample size (n=43548)+20/20
- Follow-up+10/10
100 / 100
77 / 100
- P-valuesno p-values reported
- Effect size+20/20
- Confidence intervals+15/15
- Pre-registration+15/15
Each component is scored out of 100 and then capped by the study design — a case series cannot reach the ceiling a randomised trial can, however well it is reported.
Where it sits
RCT reviewsReviews of RCTs (Meta-analyses)
Max 100Randomized TrialsRandomized Trials
Max 90Reviews of Cohort StudiesReviews of Cohort Studies
Max 85Cohort StudiesCohort Studies
Max 72Reviews of Case-Control StudiesReviews of Case-Control Studies
Max 63Case-Control StudiesCase-Control Studies
Max 58Cross-Sectional & Case SeriesCross-Sectional & Case Series
Max 50Expert OpinionExpert Opinion
Max 572 / 100
Probability of being correct
Participants are randomly assigned to treatment or control groups, minimizing bias. The gold standard for testing whether an intervention causes an effect.
This design can establish causation. The study is a randomized, placebo-controlled, observer-blinded trial, which supports causal inference for the primary efficacy endpoint (prevention of laboratory-confirmed Covid-19). However, limitations include observer-blinding only, short median follow-up of 2 months, and abstract-only review, so causal claims should be restricted to the specific endpoint and population studied.
Major COI
Major conflicts that significantly reduce study credibility
The study was funded by BioNTech and Pfizer, the manufacturers of the vaccine being tested, indicating a major conflict of interest due to industry sponsorship.
Funders
Conflict Details
BioNTech and Pfizer: Funded the study (sponsor)
The study is a pivotal efficacy trial for the BNT162b2 vaccine, funded by its manufacturers. No conflict of interest or author affiliation disclosures are included in the provided text, so author employment by the funders cannot be confirmed from this excerpt. The funders' role in study design, data analysis, or publication decisions is not described. The trial is registered (NCT04368728).
Standing
The people behind it
The researchers who wrote the study this analysis is built on.
Authored by
29 researchersIf this is your work, this is how we attribute it on Fit Body Science. Fernando P. Polack is listed as the lead author.