COVID vaccine effectiveness declines after 6 months without boosters: Providence study
A study released in The Lancet Respiratory Medicine by Providence, one of the largest health systems in the United States, confirms the overall effectiveness of vaccines in preventing severe infection resulting in hospitalization from Covid-19, but also shows a substantial decline in protection after six months. Completed by a team of clinicians and scientists in the Providence Research Network, the study examined data from nearly 50,000 hospital admissions between April and November of 2021, finding that vaccines were 94% effective at preventing hospitalization 50-100 days after receiving the shot but fell to 80.4% 200-250 days later, with even more rapid declines after 250 days.
In addition to examining the effectiveness of vaccines over time, the Providence study was also able to identify factors associated with reduced vaccine effectiveness. Key risk factors for a severe "breakthrough" infection included advanced age (80+), comorbidities such as cancer, transplants, chronic kidney disease, hypertension, or heart failure, the amount of time that had elapsed since being vaccinated, and the type of vaccine one received. For the latter factor, the study found that the Moderna vaccine offered the best overall protection over time, while the Pfizer-BioNTech vaccine offered initial protection equivalent to Moderna's but declined more rapidly over time. Persons receiving the Janssen vaccine also had higher odds of experiencing a severe breakthrough infection compared to Moderna.
https://www.thelancet.com/journals/lanres/article/PIIS2213-2600
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