Scientists from Kaiser Permanente found that Pfizer BioNTech COVID-19 booster doses strongly improve protection against omicron.
But the protection seems to wane after 3 months against emergency room visits, and even for hospitalization.
The research is published in The Lancet Respiratory Medicine and was conducted by Sara Y. Tartof et al.
In the study, the team found a booster dose of the Pfizer COVID-19 vaccine provides strong protection, roughly 80% to 90%, in the first few months against severe diseases caused by the delta and omicron variants.
However, against omicron, this protection wanes over time—even after a third dose.
Trends in waning against delta-related outcomes were generally similar to omicron, but with higher effectiveness at each time point than those seen for omicron.
In this study, the team analyzed 11,123 hospital admissions and emergency department visits that did not result in hospital admission for acute respiratory infection.
The study focused on patient records in Southern California from December 1, 2021, through February 6, 2022, when both the delta and omicron variants were circulating.
They found after 2 doses of the Pfizer COVID-19 vaccine effectiveness against omicron was 41% against hospital admission and 31% against emergency department visits at 9 months.
After 3 doses, effectiveness against omicron-related hospitalization was 85% at less than 3 months but fell to 55% at 3 months or longer.
The team also found vaccine effectiveness of 3 doses against omicron was 77% at less than 3 months but fell to 53% at 3 months or longer.
They say although the Pfizer COVID-19 protection levels against omicron after 3 doses are substantially higher than those seen after 2 doses, they are less than those observed for delta or other COVID-19 strains.
Additional doses of current, adapted, or novel COVID-19 vaccines may be needed to maintain high levels of protection against subsequent waves of COVID-19 caused by omicron or future variants with similar potential to escape protection.
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