There has been some concern among scientists and, well, the general public, that the COVID-19 vaccines might not be working as well anymore. But researchers at the University of California San Diego may have found out why that is.

Why is COVID vaccine efficacy getting worse?

The UCSD researchers recently published a letter that talked about why the COVID-19 vaccines may wane over time, according to NBC San Diego.

The researchers identified two major reasons:

  1. The delta variant started to surge in the summer.
  2. The United States loosened masking and restrictions.

The researchers published the letter in The New England Journal of Medicine. They monitored how well the vaccine protected health care workers at UCSD, specifically looking at when the highly contagious delta variant started to rise.

  • The research team found that the vaccine effectiveness stops symptomatic COVID-19 infection by 90%. In July, that number dropped to 65%, NBC San Diego reports.
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Dr. Nancy Binkin, one of the study’s author and a professor of epidemiology in the school of medicine at UC San Diego, said a number of factors led to the vaccine being less effective.

  • “The dramatic change in vaccine effectiveness from June to July is likely due to a combination of factors,” Binkin said. “It’s the emergence of the delta variant and waning immunity over time, compounded by the end of broad masking requirements and the resulting greater exposure risk throughout the community.”

Is COVID immunity waning?

That said, there are some scientists who question whether vaccine and immunity is really waning among vaccinated people. Experts told The New York Times that immunity might drop off, but the fall off has not been as dramatic as we think it is.

Scientists told The New York Times that there is not enough data about the side effects of booster shots, or if booster shots are needed for everyone.

  • “There’s a big difference between needing another shot every six months versus every five years,” Dr. David Dowdy, an epidemiologist at Johns Hopkins University, told The New York Times. “So far, looking at the data we have, I’m not seeing much evidence that we’ve reached that point yet.”
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Deepta Bhattacharya, a bioimmunologist at the University of Arizona, recently told NPR that the reports of waning immunity might be overblown, too.

  • “If you get a big dose of delta, as the variant often gives, the virus can slip past the initial wall of antibodies,” he told NPR. “So I think we may be seeing some signs of that. But the (level of breakthrough infections) is probably not as dramatic as I think it’s being made out to be.”
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