Real-World Data Suggests Two Doses of Pfizer Vaccine Provides Over 95% Protection

An observational study published in The Lancet has explored the real-world effectiveness of the Pfizer–BioNTech mRNA COVID-19 vaccine (BNT162b2) against a variety of outcomes.

Vaccines in exchange for data

As of May 6, Israel has vaccinated the highest proportion of its population compared to any other country in the world.

While there are now several COVID-19 vaccines authorized, Israel is administering only BNT162b2 as part of an exclusive agreement between the Israeli Ministry of Health and Pfizer/BioNTech. The agreement would secure vaccine supplies for the country in exchange for real-world epidemiological data, such as the new study published today in The Lancet.

BNT162b2 "highly effective" according to real-world data

The study used national surveillance data from Jan 24 to April 3, 2021 to investigate the effectiveness of BNT162b2 in a real-world setting against six different outcomes, including:

• Asymptomatic infection
  
  
• Symptomatic infection
  
  
• COVID-19-related hospitalization
  
  
• Severe or critical hospitalization and
  
  
• Death
  

As of April 3, 72% of adults aged 16 years and over, and 90% of adults aged 65 and over had received two doses of BNT162b2. Israel opted to conform to the clinical trial schedule and administered the second dose of the vaccine 21 days after the initial dose. "The start of the study period corresponded to 14 days after the first individuals received their second BNT162b2 dose," the authors write.

During the study period, there were 232,268 SARS-CoV-2 infections, 7,694 COVID-19 hospitalizations, 4,481 severe or critical COVID-19 hospitalizations and 1,113 COVID-19 deaths in individuals aged 16 years and over. Analysis of this data suggests that two doses of the mRNA-based vaccine prove 95% effective against SARS-CoV-2 infection, hospitalization and death resulting from infection.

In contrast, one dose of the vaccine provided 58% protection against infection, 76% against hospitalization and 77% against death. "The results show that people need to receive the second dose for full effectiveness," Dr Gillies O’Bryan-Tear, from the Faculty of Pharmaceutical Medicine said.

O'Bryan-Tear added, "These results mirror the clinical trial data (although the trial did not analyse asymptomatic infection) and were seen across all age groups above 16 years and demonstrate the outstanding effectiveness of this mRNA vaccine in a real-world vaccination campaign."

Protection against variants

The data demonstrates BNT162b2's effectiveness against variants of the SARS-CoV-2 virus. During the study period, the B.1.1.7 strain (also known as the "Kent" variant") was dominant in Israel. Cases of the B.1.351 variant were also reported during the study, however these figures were too small to conduct efficacy analysis.

The authors acknowledge that the observational nature of the research incurs several limitations: "In the absence of randomization, there could have been unmeasured differences between vaccinated and unvaccinated persons (e.g., different test-seeking behaviors or levels of adherence to non-pharmaceutical interventions) which might have confounded our vaccine effectiveness estimates," they write.

Discussing these potential limitations, Dr Peter English, retired consultant in communicable disease control, stated, “The authors address these clearly in their discussion; in short, while cofounders are not completely eliminated, the quality of Israel’s data collection systems and the large numbers mean that they are unlikely to have contributed significantly to the results, and the results are thus robust."

"This population study provides something for everyone: for those who have been critical of the UK stance of providing first doses to as many as possible and delaying the second dose, the results show that people need to receive the second dose for full effectiveness (duration of effect is not addressed in this study since follow up was insufficient)," added O'Bryan-Tear. He continued by stating that proponents of delaying the second dose can "draw comfort" from the fact that even one dose of the mRNA COVID-19 vaccine was substantial against the severe endpoints of the study: hospitalization and death.

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Reference: Haas EJ, Angulo FJ, McLaughlin JM, et al. Impact and effectiveness of mRNA BNT162b2 vaccine against SARS-CoV-2 infections and COVID-19 cases, hospitalisations, and deaths following a nationwide vaccination campaign in Israel: an observational study using national surveillance data. The Lancet. doi:10.1016/S0140-6736(21)00947-8.