Study Finds Half-Dose of COVID-19 Booster Equally Effective as Full Dose
The study found that a half-dose of the Pfizer COVID-19 booster vaccine can elicit a comparable immune response in adults compared to a full dose, with fewer side effects. New research led by the Murdoch Institute and the National Centre for Communicable Diseases in Mongolia involved 601 participants over 18 years old from Mongolia. It is the first to compare widely used COVID-19 vaccines in low- and middle-income countries and focused on adults who had previously received AstraZeneca or Sinopharm COVID-19 shots. Reduced doses would make booster programs more cost-effective and may improve COVID-19 booster acceptability and uptake. Policymakers and immunisation advisory committees can use this data to make flexible boosting schedule decisions.
However, the study noted that half-dose boosting may be less effective in adults primed with the Russian COVID-19 vaccine, Sputnik V. Participants receiving half doses reported fewer side effects compared to those receiving full doses, highlighting the potential benefits of this approach. Among half-dose boosted participants, 60 percent reported local reactions including pain and tenderness, and 25 percent reported systemic reactions including fevers, vomiting, diarrhea, and headaches. On the other hand, 72 percent of full-dose boosted participants reported local reactions, and 32 percent reported system reactions. The study will continue to follow up on participants at six and 12-month intervals to explore their immune response, such as waning rates and breakthrough infections.
This comes amid recommendations from the Food and Drug Administration’s (FDA) vaccine adviser Dr. Paul Offit, who stated that most people do not need another COVID-19 booster. An international clinical trial funded by the Coalition for Epidemic Preparedness Innovations (CEPI) involving 3,300 healthy adults across Australia, Indonesia, and Mongolia is investigating the impact of administering a reduced dose of COVID-19 booster shots. The efficacy, side effects, and acceptability of fractional doses explored will inform flexible booster strategies and address global vaccine supply challenges. CEPI receives funding from the Australian government.
