Studies made by the U.S. Centers for Disease Control and Prevention and British scientists seem to point that the effectiveness of COVID-19 vaccines declines over time as the highly transmissible Delta variant sweeps across the United States.
Protection offered by two doses of the Oxford/AstraZeneca and Pfizer/BioNTech vaccines starts to wane within six months, highlighting the need for booster shots, researchers in Britain said.
One study, which focused on frontline medical care personnel, found that vaccine effectiveness decreased by almost 30 percentage points since the Delta variant emerged as the dominant strain in the U.S.
The analysis, published in the CDC's Mortality and Morbidity Weekly Report, also concluded that the vaccines were 80 % effective in preventing infection among frontline health workers.
A second study found that 25% of cases between May and July in Los Angeles were breakthrough ones, but that hospitalizations significantly dropped for people who had been immunized, The Politico reported.
Those that have not been inoculated were nearly 30 times more likely to be hospitalized than immunized people, and about five times more likely to get the virus.
However, researchers at CDC said the trend should be "interpreted with caution" because a drop in vaccine effectiveness could be the result of "poor precision" in estimates because of limited observation period and few cases among patients.
According to Dr. Eric Topol, a professor of molecular medicine, the analysis shows the importance of being fully inoculated because the benefit of being vaccinated when it comes to being hospitalized did not decrease even with the recent wave of COVID-19.
"The benefit of being fully immunized is still there despite the breakthrough cases because hospitalizations are really markedly protected," Topol, who is also vice president for research at the Scripps Research Institute, said in quotes by USA Today.
Meanwhile, an analysis from the United Kingdom's ZOE COVID-19 app study of more than 400,000 participants who had been administered with shots of the Pfizer/BioNTech vaccine, showed it was 88% effective in protecting against the virus a month after receiving both jabs. However, its effectiveness declined to 75% five or six months after receiving both shots of the vaccine.
