Two Doses of Pfizer-BioNTech Vaccine Protect Against COVID-19 Hospitalizations for 6 Months


This study confirmed reports from the CDC and Israel Ministry of Health that found the Pfizer-BioNTech vaccine waned after 6 months.


Two doses of the Pfizer-BioNTech (BNT162b2) vaccine protect against COVID-19 hospitalization for at least 6 months, according to a study by Kaiser Permanente and Pfizer and the results published in The Lancet.

The study shows that vaccine efficacy waned significantly, from 88% within one month of receiving the second dose to 47% by the end of the six-month study period.

However, the vaccine’s protection against hospitalizations for the six-month study period was 90%.

The efficacy remained consistent for all strains of COVID-19, including the Delta variant. The investigators did not notice a difference in vaccine waning between variants, but this result may have been affected by Delta becoming the dominant variant by the middle of the study period.

The study examined 3,436,957 electronic health records from the Kaiser Permanente Southern California (KPSC) health system from December 4, 2020-August 8, 2021. During this study period, 5.4% (184,041) were infected with COVID-19, and among these 6.6% (12,130) were hospitalized. The average time since being fully vaccinated was three to four months.

Genome sequencing and viral lineage analysis of PCR-positive samples from the study cohort showed the more infectious Delta variant was responsible for 28% of the cases within the sample. As Delta became the dominant strain in the US, the proportion of positive cases increased from 0.6% in April 2021 to 87% in July 2021.

Vaccine efficacy against Delta was 93% one month after receiving both doses and 53% after four months. For other variants, efficacy was 97% after one month and 67% after four months. The vaccine remained 93% effective against Delta-related hospitalizations for the entirety of the study.

According to Luis Jodar, senior vice president and chief medical officer of Pfizer Vaccines, “COVID-19 infections in people who have received two vaccine doses are most likely due to waning and not caused by Delta or other variants escaping vaccine protection.”

Immunity waned for all age groups throughout the study period, reopening discussions about who should be eligible for a booster shot.

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