In a new study from Johns Hopkins, researchers found that while COVID-19 vaccines lose some effectiveness in preventing SARS-CoV-2 infection, the vaccines retain nearly all of their ability to prevent severe disease up to six months after full vaccination.
They analyzed vaccination effectiveness data published last year from June 17 to December 2.
The data covered dozens of individual vaccine evaluations preceding the emergence of the currently dominant Omicron variant.
The researchers found that the level of protection from SARS-CoV-2 infection fell by about 21 percentage points, on average, in the interval from one to six months after full vaccination.
But the level of protection against severe COVID-19 fell by only about 10 percentage points in the same interval.
The authors defined “full vaccination” as one dose of the Janssen vaccine or two doses of other vaccines. Booster doses were not evaluated.
How long vaccines protect from infection and severe disease is one of the most urgent questions in the COVID-19 pandemic.
The finding that protection dropped against detected infection by an average of 21.0 percentage points over five months means that a vaccine providing 90 percent protection from infection at 1 month would provide only 69 percent protection at 6 months.
The average drop was essentially no different among vaccinated persons older than 50 when analyses were restricted to just their data.
Similarly, protection against symptomatic illness from SARS-CoV-2 infection—which includes both mild and severe illness—dropped on average by 24.9 percentage points among persons of all ages, and 32.0 percentage points among older persons, from one month to six months post-vaccination.
Public health officials often emphasize vaccination for its protection against severe COVID-19. F
or this more serious outcome, vaccine protection apparently was more durable, with effectiveness dropping on average by just 10 percentage points during the one- to the six-month interval.
The slight drop was similar for older persons who are at increased risk for severe COVID-19 outcomes.
The study is broadly consistent with others that have looked at vaccine effectiveness over time, and suggests that the four vaccines on average, during pre-Omicron waves, have provided good protection against the severe outcomes that are most relevant to public health concerns.
If you care about COVID, please read studies about new ways to predict who will get severe COVID-19 and die, and why people with blood Type O less likely to get COVID-19.
For more information about health, please see recent studies about new drug that could prevent COVID-19, and results showing that for people over 50, even ‘mild’ COVID 19 can cause dangerous health problems.
The study is published in The Lancet and was conducted by Melissa Higdon et al.
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