Coronavirus Facts and Myth Buster

With inputs from Dr Monica Vasudev

US FDA cautions about antibody tests to assess immunity among the vaccinated

In a safety communication, the US FDA has recommended against using currently authorized SARS-CoV-2 antibody tests to assess immunity after COVID-19 Vaccination.

  • A positive antibody test helps identify people who may have had a prior SARS-CoV-2 infection; however, more research is needed in people who have received a COVID-19 vaccination to understand the meaning of a positive or negative antibody test, beyond the presence or absence of antibodies.
  • A positive antibody test can indicate an immune response has occurred (seroconversion); failure to detect such a response may suggest a lack of immune response. More research is needed.
  • Vaccines trigger antibodies to specific viral protein targets. COVID-19 vaccinated people who have not had previous natural infection will receive a negative antibody test result if the antibody test does not detect the antibodies induced by the COVID-19 vaccine.
  • Currently authorized SARS-CoV-2 antibody tests have not been evaluated to assess the level of protection provided by an immune response to COVID-19 vaccination.
  • If antibody test results are interpreted incorrectly, there is a potential risk that people may take fewer precautions against SARS-CoV-2 exposure, which can increase their risk of SARS-CoV-2 infection and may result in the increased spread of SARS-CoV-2.

(Source: US FDA, May 19, 2021)

New CDC definition of post-vaccine “Breakthrough case” 

The CDC has changed its definition of a breakthrough case after COVID-19 vaccination. As of May 1, 2021, CDC has shifted its approach from monitoring all reported vaccine breakthrough cases to focus on identifying and investigating only hospitalized or fatal cases due to any cause. The is to focus on cases of clinical and public health importance.

“For the purpose of this surveillance, a vaccine breakthrough infection is defined as the detection of SARS-CoV-2 RNA or antigen in a respiratory specimen collected from a person ≥14 days after they have completed all recommended doses of a U.S. Food and Drug Administration (FDA)-authorized COVID-19 vaccine.”

Out of 101 million fully vaccinated individuals, around 10,000 reported a breakthrough infection. Of specimens available for sequencing, 64% were variants of concern, as per data from the Morbidity and Mortality Weekly Report (Source: CDC).

Cancer or COVID vaccine? Pitfalls of PET imaging after recent Covid-19 vaccination in cancer patients

Positron emission tomography (PET) imaging of cancer patients after COVID-19 vaccination has shown abnormal radiotracer uptake in lymph nodes.

  • In a retrospective study, 67 patients (mean age 76 years) underwent PET imaging from December 14, 2020 to March 10, 2021, following vaccination with either the Pfizer or Moderna COVID-19 vaccine. They had no visible axillary node uptake on pre-vaccination PET.
  • PET was performed a median of 13 days after vaccination in 44 patients who had received one vaccine dose, and 10 days in 23 patients who had received two doses.
  • Positive axillary lymph node uptake was seen in seven (10.4%) patients, four of whom had FDG-PET exams (out of 54 patients), and three of whom had choline C-11 exams (out of 13).
  • Ipsilateral deltoid uptake was observed in 14.5% of patients with documented injection laterality, including three of the seven patients with positive axillary lymph nodes.
  • One patient exhibited extra-axillary lymph node uptake (ipsilateral supraclavicular uptake on FDG PET).
  • This “could prompt unnecessary biopsies and treatments unless appropriately recognized by interpreting physicians”, say study authors.
  • Physicians should recognize characteristics of abnormal uptake on PET after COVID-19 vaccination to guide optimal follow-up management and reduce unnecessary biopsies.

(Source: Schroeder DG, et al. Frequency and characteristics of nodal and deltoid fdg and 11c-choline uptake on PET imaging performed after COVID-19 vaccination. AJR Am J Roentgenol. 2021 May 19. doi: 10.2214/AJR.21.25928).

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