This Vaccine's Effectiveness Against COVID Drops the Most, New Study Says

New research shows this vaccine loses the most protection against infection over time.

While vaccinated people still remain heavily protected against severe COVID cases, it's become clear over the past few months that protection against any infection may not be as strong as it once was. Breakthrough COVID cases have hit millions of people in the U.S., and while the vast majority are mild, you still probably want to know how protected you are against getting sick. Recent research has shown that time, age, and the Delta variant have all played a role in these breakthrough cases, but now a new study has found that your ability to stave off infection over time may also depend on which COVID vaccine you received.

RELATED: If You Got Pfizer, This Is When Your Protection Plummets, New Research Says.

Researchers from the New York State Department of Health (DOH) released what they're dubbing the largest U.S. study by vaccine type and timing of vaccination on Oct. 9, as a preprint on medRxiv. The DOH determined vaccine effectiveness by analyzing more than 8.8 million New York adults from January to August through statewide testing, hospital, and vaccine registry databases.

The researchers recorded more than 38,000 breakthrough infections among the more than 5.7 million fully vaccinated individuals in the study. According to the study, Pfizer's vaccine effectiveness decreased the most over time for all age groups. For Pfizer recipients 18 to 49 years old, there was a 24.6 percent reduction in vaccine effectiveness, a 19.1 percent decrease for those 50 to 64 years old, and a 14.1 percent reduction for those 65 years and older.

Moderna and Johnson & Johnson's effectiveness got lower over time as well, but only 18 percent and 19.2 percent, respectively, for those 18 to 49 years old; 11.6 percent and 10.8 percent, respectively, for those 50 to 64 years old; and 9 percent and 10.9 percent, respectively, for those 65 years and older.

"By analyzing large cohorts of [New York State] residents, we observed substantial declines in [vaccine effectiveness] for COVID-19 cases from May to August 2021. These declines occurred simultaneously across age, product, and time-cohort, with the largest declines seen for Pfizer-BioNTech recipients," the study authors concluded.

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The researchers say that their findings largely align with recent decisions to approve an additional Pfizer booster shot for certain individuals. "Pfizer-BioNTech booster doses have been demonstrated safe and to increase short-term protection against the Delta variant," the study authors wrote, nothing that their study demonstrates the need for Pfizer boosters in those over 65 years old.

According to the study, Pfizer still remains quite protective against severe COVID for younger individuals, but they did find "modest declines" for hospitalization rates among Pfizer and Moderna recipients 65 years or older. For this older age group, vaccine effectiveness against hospitalization during May to August dropped from 95 percent to 89.2 percent for Pfizer recipients, and from 97.2 percent to 94.1 percent for Moderna recipients.

"We saw limited evidence of decline in effectiveness against severe disease for people ages 18 to 64 years old," lead study author Eli Rosenberg, MD, said in a statement. "While we did observe early declines in effectiveness against infections for this age group, this appears to have leveled off when the Delta variant became the predominant strain in New York. Together, this suggests that ongoing waning protection may be less of a current concern for adults younger than 65 years."

RELATED: This Is the Only COVID Vaccine That's More Effective Over Time, CDC Says.

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