1. Despite waning effectiveness against SARS-CoV-2 infection, fully vaccinated patients continued to show low COVID-19 hospitalization rates up to 5 months after vaccination.
2. Vaccine effectiveness against infections decreased from 88% to 47% within first five months.
Evidence Rating Level: 2 (Good)
Study Rundown: There is limited evidence surrounding the efficacy of BNT162b2 (Pfizer-BioNTech vaccine) for novel SARS-CoV-2 strains, such as the delta (B.1.617.2) variant. Similarly, as vaccine distribution continues globally, more evidence is needed to elucidate the long-term efficacy of the BNT162b2 vaccine in the context of waning immunity. Moreover, whether the rise in SARS-CoV-2 is due to vaccine-resistant strains or waning vaccine-related immunity has not been unexplored. Consequently, this retrospective study aimed to determine the overall and variant-specific effectiveness of the BNT162b2 against SARS-CoV-2 infections. Co-primary endpoints included PCR-confirmed SARS-CoV-2 infections and COVID-19 related hospitalizations. According to the study results, full vaccination status was highly protective for SARS-CoV-2 infection and COVID-19-related hospital admission, although effectiveness decreased within the first five months of vaccination. Despite decreasing effectiveness against SARS-CoV-2 infection, protection from COVID-19 related hospitalizations remained high up to 5 months after vaccination. These trends in vaccine effectiveness were similar for both delta and non-delta variants. This study was strengthened by a large sample of patients, increasing the validity of findings.
Relevant Reading: Safety of the BNT162b2 mRNA Covid-19 Vaccine in a Nationwide Setting
In-depth [retrospective cohort]: Between Dec 14, 2020, and Aug 8, 2021, 4 920 549 patients were assessed for eligibility. Included were those ≥12 years old who were members of Kaiser Permanente Southern California (KPSC) for ≥1 year. Altogether, 3 436 957 patients were enrolled. Median age among those enrolled was 45 years (interquartile range [IQR] 29-61) and the majority (52.4%) were female. Co-primary endpoints of effectiveness against SARS-CoV-2 infections (73%, 95% confidence interval [CI] 72-74) and COVID-19 related hospital admissions (90%, 95% CI 89-92) were high among vaccinated patients. Overall vaccine effectiveness decreased from 88% (95% CI 86-89) to 47% (95% CI 43-51) within first five months, as did the effectiveness against delta (93%, 95% CI 85-97 to 53%, 95% CI 39-65) and non-delta (97%, 95% CI 95-99 to 67%, 95% CI 45-80) variants. Nevertheless, vaccine effectiveness against COVID-19 related hospitalization at 4-5 months after vaccination remained high for the delta variant (93% [84-96%]). Findings from this study suggest that BNT162b2 (Pfizer-BioNTech) vaccine is effective against most viral strains up to 6 months after the initial dose. However, study results may suggest a need to consider booster doses in the context of waning vaccine efficacy.
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