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A study published Monday in the medical journal The Lancet found that the effectiveness of the Pfizer-BioNTech COVID-19 vaccine fell below 50% after about six months after the second dose.
The Pfizer-funded study found that Pfizer’s vaccine was 88 percent effective in the first month after the full vaccination, but fell to 47 percent effectiveness after about six months. The vaccine was also found to be very effective against the delta variant, which was found to be over 90 percent effective in the first few months before dropping to 53 percent after four months.
The researchers determined that the decline in immunity was related to the time since an individual received the second injection rather than the highly infectious delta strain.
“Our results confirm the high efficacy of [Pfizer-BioNTech COVID-19 vaccine] against hospital admissions for up to about 6 months after being fully immunized, even in the face of widespread spread of the delta variant, ”the researchers wrote. “The reduction in vaccine efficacy against SARS-CoV-2 infections over time is likely primarily due to the decline in immunity over time rather than the delta variant escaping vaccine protection.”
Protection against hospitalization remained high throughout treatment, being 93 percent effective for up to six months after administration.
For the study, researchers examined electronic records from the Kaiser Permanente Southern California (KPSC) health system, examining all patients in the system aged 12 and older. The researchers looked at 3.4 million people in the KPSC healthcare system that they studied from December 2020 to last August.
Researchers determined that people fully vaccinated with the Pfizer-BioNTech vaccine had 73% effective overall protection against COVID-19 infection and 90% effective protection against COVID-19-related hospitalizations.
“Our results reiterate in a real American context that vaccination with [the Pfizer-BioNTech COVID-19 vaccine] remains an essential tool to prevent COVID-19, particularly hospitalizations associated with COVID-19, caused by all current variants of concern, ”they wrote.
The results of these studies reiterate the findings of Pfizer and BioNTech that were published in July. The preprint study found that the vaccine’s efficacy peaked at 96.2% within two months of the second dose, with the vaccine’s efficacy decreasing at the time by about 6 percentage points every two months thereafter.
The results of this study are released just weeks after the Food and Drug Administration approved a booster dose of Pfizer’s coronavirus vaccine for the elderly and those at high risk of infection, with the decision being made in light previous data suggesting that the vaccine’s efficacy dropped after a few months.
“We believe boosters have an important role to play in tackling the continuing threat of this disease, alongside efforts to increase global access and adoption among the unvaccinated,” said at the time the CEO of Pfizer, Albert Bourla.
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