As cases of the coronavirus continue to climb, new evidence is showing that the vaccines are less effective at preventing infection from the delta variant.
The delta variant is more contagious than the previous strains of COVID-19 that have been detected in the U.S. It's also causing more severe illness and causing hospitalizations to increase. Those states that have lower COVID-19 vaccination rates are where the delta variant is spreading the most.
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New data from the Mayo Clinic indicates that the effectiveness of the two-dose Pfizer vaccine dropped from 76% earlier this year to 42% in July amid the emergence of the delta variant. The Moderna vaccine declined from 86% to 76%. Researchers examined the records of more than 25,000 patients in Minnesota to reach their conclusion.
According to the study, individuals who received the Moderna vaccine are about half as likely to experience breakthrough infections as those who received the Pfizer vaccine.
While research suggests that COVID-19 vaccines are less effective against preventing breakthrough infections involving the delta variant, scientists say the vaccines still appear to provide protection against severe COVID-19 symptoms and hospitalization.
The Pfizer vaccine was 85% effective at preventing hospitalizations earlier this year -- that dropped down to 75% in July, according to the study. For Moderna, it was 91% effective at preventing hospitalizations earlier this year and 81% effective in July.
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The study authors said both vaccines "were originally designed, tested, and proven to reduce the burden of symptomatic disease, hospitalization, and death related to SARS-CoV-2 infection. This study further supports the effectiveness of both vaccines in doing so, even despite the evolution of more transmissible viral variants."
The authors also point out that most vaccines are not 100% effective, particularly against asymptomatic infections.
"For example, the estimated effectiveness of seasonal influenza vaccines has ranged from 19-60% over the past decade," the authors said. "While COVID-19 mRNA vaccines have been shown to be drastically more effective than this, the occurrence of breakthrough infections is indeed still expected."
The study did not look at the effectiveness of the one-dose Johnson and Johnson vaccine. The authors also note that further research is needed with more diverse populations to guide public health decisions, such as the optimal timing for booster doses and which vaccines should be administered to individuals who have not yet received one dose.
Latest figures from the Centers for Disease Control and Prevention show 71.5% of U.S. adults have received at least one dose of vaccine and 61.3% are considered fully vaccinated. Of those who are vaccinated, 89.6 million have received the Pfizer vaccine, 64 million have received the Moderna vaccine and 13.5 million have received the Johnson and Johnson vaccine.
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