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The United States is gearing up to provide boosters to all Americans who received the Pfizer-BioNTech and Moderna vaccines after recent reports suggested immunity wanes after 8 months.

In a small study published in the medRxiv* preprint server, people given a booster Johnson & Johnson shot showed elevated and robust antibody levels.

The authors write:

While it remains to be seen whether a third booster dose is needed, we illustrate here that should it be required, such a strategy strongly bolsters antibody responses and could therefore be another instrument in the arsenal for full control of this pandemic.”

The results suggest a booster shot can augment immunity against severe acute respiratory syndrome 2 (SARS-CoV-2) – the virus that causes coronavirus disease 2019 (COVID-19) – and may increase protection against multiple variants, including the Delta (B.1.617.2) variant.

Study: A third COVID-19 vaccine shot markedly boosts neutralizing antibody potency and breadth. Image Credit: Kateryna Kon / Shutterstock

Study details

The study followed four healthy individuals with no antibodies against SARS-CoV-2, indicating that any antibody levels came solely from vaccination. All four individuals received a Johnson & Johnson booster shot after being fully vaccinated with the two-dose Pfizer vaccine.

Previous studies showed practical benefits for using a mix-and-match vaccine schedule, supporting the decision to use a Johnson & Johnson for the third vaccination.

The first Pfizer-BioNTech dose was administered in December 2020, and the second dose was given 3 weeks after the first dose in January 2021. The Johnson & Johnson booster shot was administered 4 months after the second vaccination in May 2021.

Convalescent plasma was taken from all four individuals to assess antibody levels. Samples were taken after the second vaccination, 16 weeks after the second vaccination, 2 weeks after the third vaccination, topamax pill and 4 weeks after the third vaccination. Antibodies specific for SARS-CoV-2 spike protein and nucleoprotein were assessed using enzyme-linked immunosorbent assay (ELISA).


All 4 individuals had antibodies specific for the SARS-CoV-2 spike protein after all tested time points. In addition, antibodies were detected for both the non-variant SARS-CoV-2 strain and the Beta (B.1.351) variant.

Four months after their second vaccination, antibody levels dropped. However, antibody levels increased and remained high after a third vaccination.

The Johnson & Johnson booster shot increased antibody levels to a level higher than observed with two vaccines.

Except for one volunteer, antibodies after the third vaccination had strong neutralizing activity against all variant pseudoviruses, including the Delta variant. Only one volunteer did not have sufficient neutralizing antibodies against the Beta variant.

The highest antibody titers were against the non-variant strain and the Alpha (B.1.1.7) variant.

The increases in plasma neutralization titers (ID50) ranged from 10.9 to 21.1-fold in the pseudovirus neutralization assay and 14.8 to 32.4-fold in the authentic virus neutralization assay. One individual, Volunteer #1, even had heightened neutralizing titer against SARS-CoV.”

*Important notice

medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

Journal reference:
  • Iketani S, et al. A third COVID-19 vaccine shot markedly boosts neutralizing antibody potency and breadth. medRxiv, 2021. doi:,

Posted in: Medical Science News | Medical Research News | Disease/Infection News

Tags: Antibodies, Antibody, Assay, Convalescent Plasma, Coronavirus, Coronavirus Disease COVID-19, Enzyme, immunity, Pandemic, Protein, Pseudovirus, Respiratory, SARS, SARS-CoV-2, Severe Acute Respiratory, Severe Acute Respiratory Syndrome, Spike Protein, Syndrome, Vaccine, Virus

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Jocelyn Solis-Moreira

Jocelyn Solis-Moreira graduated with a Bachelor's in Integrative Neuroscience, where she then pursued graduate research looking at the long-term effects of adolescent binge drinking on the brain's neurochemistry in adulthood.

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