Waning of Pfizer-BioNTech Vaccine against COVID-19 Infection in Qatar

Vaccine efficacy waning over time is a growing international concern. While two doses of the Pfizer-BioNTech (BNT162b2) vaccine have been proven effective for at least six months, many fully vaccinated populations are reaching this cutoff and experiencing a loss of COVID-19 immunity.

Qatar launched a widescale immunization campaign in late December 2020, first with the Pfizer-BioNTech vaccine and then with the Moderna (mRNA-12733) vaccine three months later.

As of September 7, 2021, an estimated 90% of people 12 years and older had received at least one vaccine dose, and 80% were fully vaccinated, giving Qatar the highest mRNA coverage worldwide.

However, Qatar experienced two extreme waves of COVID-19 January-June 2021. By the summer of 2021, the Delta (B.1.617.2) variant had become the dominant strain.

A study published today in The New England Journal of Medicine sought to assess the real-world efficacy of the Pfizer-BioNTech vaccine against COVID-19 infection, hospitalization, and death.

Funded by Weill Cornell Medicine-Qatar, investigators used a matched test-negative, case-control study, a technique commonly used to estimate vaccine effectiveness against influenza. They extracted data on the resident population of Qatar from their comprehensive COVID-19 database.

Case participants (PCR-positive people) and controls (PCR-negative people) were matched one-to-one by sex, 10-year age group, nationality, reason for PCR testing, and calendar week of PCR test.

By the end of the study on September 5, 2021, a total of 8203 breakthrough infections were recorded among people with one dose of the vaccine, and 10543 breakthrough infections among people who received both doses of the vaccine. The daily percentage of breakthrough infections eventually reached 36.4% on the final day of the study.

Investigators found that 77.2% of Qatar’s breakthrough infections were recorded for the Pfizer-BioNTech vaccine. Efficacy of Pfizer-BioNTech against COVID-19 reached its peak at 77.5% (95% CI, 76.4 to 78.6) the first month after the second dose. Subsequently, vaccine efficacy declined gradually, accelerating after the fourth month, and reaching a low of 20% 5-7 months after full vaccination.

At its peak, Pfizer-BioNTech was 81.5% effective against symptomatic COVID-19, and 73.1% effective against asymptomatic infection. Protection against severe, critical, or fatal COVID-19 peaked at 96% or higher two months after a second Pfizer-BioNTech dose. Notably, effectiveness against hospitalization and death did not decline over time, except potentially in the seventh month after full vaccination. Age did not appear to have any significant effect on vaccine efficacy.

The findings suggest that a large portion of the vaccinated population will lose protection against COVID-19 infection in the coming months, which may be accelerated by a false sense of security in fully vaccinated individuals, leading them believe they can fully resume normal social contact and do not have to adherence to safety measures.