October 7, 2021

Study suggests waning of BNT162b2 vaccine protection against SARS-CoV-2 infection, but protection against hospitalisation and death persists for 6 months

BNT162b2-induced (Pfizer-BioNTech) protection against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection appeared to wane rapidly following its peak after the second dose, but protection against hospitalisation and death persisted at a “robust level” for 6 months after the second dose, according to a study published in The New England Journal of Medicine

“BNT162b2-induced protection against infection builds rapidly after the first dose, peaks in the first month after the second dose, and then gradually wanes in subsequent months. The waning appears to accelerate after the fourth month, to reach a low level of approximately 20% in subsequent months,” reported Hiam Chemaitelly, Weill Cornell Medicine–Qatar, Doha, Qatar, and colleagues. 

Nonetheless, the researchers pointed out that “although the protection against asymptomatic infection diminished more quickly than that against symptomatic infection, as would be expected in a vaccine that prevents symptoms given infection, no evidence was found for an appreciable waning of protection against hospitalisation and death, which remained robust — generally at 90% or higher — for 6 months after the second dose.”

For the study, the researchers used a matched test-negative, case-control design to estimate vaccine effectiveness against any SARS-CoV-2 infection and against any severe, critical, or fatal case of coronavirus disease 2019 (COVID-19) from January 1 to September 5, 2021. Case participants (PCR-positive persons; n = 142,300) and controls (PCR-negative persons; n = 848,240) were matched according to sex, 10-year age group, nationality, reason for SARS-CoV-2 PCR testing, and calendar week of PCR test. The median age of the study participants was 31 years and approximately 69% were male, with the researchers noting that “study samples were representative of the distinct demographic characteristics of the population of Qatar.”

Overall, study data demonstrated that the estimated BNT162b2 effectiveness against any SARS-CoV-2 infection was negligible for the first 2 weeks after the first dose, increasing to 36.8% (95% confidence interval [CI], 33.2 to 40.2) in the third week after the first dose, and reaching its peak at 77.5% (76.4 to 78.6) in the first month after the second dose. However, effectiveness declined gradually, thereafter, to 73.2% (71.3 to 75.0) in the second month and to 69.6% (66.7 to 72.3) in the third month after the second dose. The decline accelerated after the fourth month (51.7% [45.0 to 57.6]), reaching approximately 20% in months 5 through 7 after the second dose.

Meanwhile, effectiveness against symptomatic infection was higher than effectiveness against asymptomatic infection but waned similarly. When the researchers assessed the effectiveness according to age (<60 years and ≥60 years), they observed that results for both age groups were largely similar in scale and in the pattern of declining effectiveness, and were similar to those for all participants in all age groups. 

On the other hand, assessment of effectiveness against infections by the B.1.1.7 (alpha), B.1.351 (beta), and B.1.617.2 (delta) variants revealed a similar waning pattern to that seen against any SARS-CoV-2 infection.

As for the estimated BNT162b2 effectiveness against any severe, critical, or fatal disease due to any SARS-CoV-2 infection, the researchers found that the effectiveness was negligible for the first 2 weeks after the first dose, with the effectiveness increasing rapidly to 66.1% (95% CI, 56.8 to 73.5) in the third week after the first dose and reached 96% or higher in the first 2 months after the second dose. However, unlike effectiveness against infection, effectiveness against hospitalisation and death did not decline over time, whereby the effectiveness persisted at approximately this level for 6 months. Effectiveness according to age group also showed similar results.

“In this study, we found that BNT162b2-induced protection against infection peaked in the first month after the second dose and then gradually waned month by month, before reaching low levels 5 to 7 months after the second dose. Meanwhile, BNT162b2-induced protection against hospitalisation and death persisted with hardly any waning for 6 months after the second dose,” the researchers noted. “These findings suggest that a large proportion of the vaccinated population could lose its protection against infection in the coming months, perhaps increasing the potential for new epidemic waves.”

SOURCE: The New England Journal of Medicine
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