by Kristina Fiore, Director of Enterprise & Investigative Reporting, MedPage Today August 3, 2021
With the threat of the more transmissible Delta variant and questions around waning immunity following vaccination, healthcare workers are thinking more and more about a third dose of the COVID-19 vaccine.
That's despite the many unknowns on what the true "correlates of protection" are when it comes to immunity, and a lack of hard clinical data that vaccine effectiveness is truly waning.
Still, physicians have been watching as many countries -- including Israel, and Germany, France, and the U.K. -- have pulled the trigger on booster doses, especially for more vulnerable populations. Now, they are talking about getting a "booster" for themselves -- even if they're not immunocompromised, and especially if they're 65 and older or if their antibody titers are low.
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The Caveats
The CDC warns that antibody testing shouldn't be used to determine immunity after vaccination, noted Christina Wojewoda, MD, chair of the College of American Pathologists' microbiology committee and director of the clinical microbiology laboratory at the University of Vermont Medical Center in Burlington.
There are many different assays that can measure antibody levels, and some don't even measure antibodies against the spike protein, which is what the vaccine induces. Instead, these tests look for antibodies to the nucleocapsid protein, which would only turn up positive if a person had a prior infection, Wojewoda said.