Scientists from Penn State found that protection against symptomatic COVID-19 begins to decrease after one month from initial vaccination, while immunity against severe COVID-19 remains high for about six months.
The research is published in BMC Infectious Diseases and was conducted by Dr. Catharine Paules et al.
In the study, the researchers analyzed data from 7 million unvaccinated and vaccinated people.
The latter received Pfizer-BioNTech, Moderna or Johnson & Johnson doses of the COVID-19 vaccine.
The team found the vaccines provided strong protection against COVID-19, but effectiveness waned over time.
The findings revealed that after full vaccination, immunity against COVID-19 infection decreased from 83% after the first month to 22% after five or more months.
The research included data on adults and children, aged 12 and older. The findings showed that recipients of the Moderna vaccine experienced the highest levels of protection.
Fully vaccinated individuals are defined as those who received two doses of either the Moderna or Pfizer vaccines, as well as individuals who received one dose of the Johnson & Johnson vaccine.
The researchers did not have data beyond six months, and the study did not include data on booster vaccines.
The team says it is reassuring to see that individuals vaccinated against COVID-19 maintained strong protection against hospitalization and death over time even when effectiveness against infection waned.
The researchers said that vaccines remained 90% effective against severe COVID for up to six months.
However, protection against severe COVID-19 was lower (74%) for individuals who received the Johnson & Johnson vaccine.
According to the study, immunity against COVID-19 decreased more rapidly for individuals 65 or older regardless of which vaccine they received.
The researchers noted that overall efficacy could depend on several factors, including vaccine type, patient age, emerging variants and geographic areas.
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