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New research from a team of scientists in Australia suggests that the second ‘booster’ dose of the Pfizer-BioNTech vaccine may not increase the effectiveness of the vaccine against severe acute respiratory syndrome (SARS-CoV-2), the causative agent. of coronavirus disease 2019 (COVID -19).
The results suggest that one dose of the vaccine could be sufficient to provide a robust immune response 11 days after inoculation.
The findings could help shape policy, as launch of the vaccine has been slow in countries like the United States and Canada. This could also increase with vaccine distribution efforts in developing countries where supplies have been tight.
This opens up possibilities for rapid short-term protection that could be used for “ring fencing” vaccination after an outbreak or cluster. In addition, it could be delivered to travelers in the fortnight before their planned trip. Since no immediate improvement was shown by giving a second vaccine after 3-4 weeks, it also increases the possibility of providing a single dose (at least in the short term when supplies are limited) and giving health services more flexibility in the administration of vaccines and at the time of a second dose if it is considered justified “.
The study “Reanalysis of Pfizer mRNA BNT162b2 SARS-CoV-2 Vaccine Data Fails to Find Greater Post-Booster Efficacy: Implications for Vaccination Policy and Our Understanding of Mode of Action” is available as a pre-print medRxiv* server, while the article undergoes peer review.
How they did it
The research team re-examined the Pfizer-BioNTech phase III trial data from day 1 to day 111 in the placebo and experimental groups. They also analyzed data from Moderna’s vaccine trial. However, since the number of COVID-19 cases in Moderna’s trial was low in the first weeks, they did not have enough data to assess it. Instead, the data from the Moderna trial was used for comparison purposes with the data from the Pfizer trial.
They studied the efficacy of vaccination from day 11 to day 28 and compared the efficacy of the second dose of vaccine administered on day 28 to day 111.
Pfizer vaccine shows full efficacy 11 days after vaccination
The results showed that the Pfizer-BioNTech mRNA vaccine provided a robust protective immune response 11 days after the first dose of vaccination. They also found that the second vaccination did not help increase efficacy.
Specifically, the first dose of vaccine helped develop detectable neutralizing antibodies before the second dose.
Although Moderna’s sample size was limited, compared to the Pfizer-BioNTech mRNA vaccine, there continued to be no significant difference in vaccine efficacy between days 11 to 35 and 7 days after administration of the vaccine. second vaccine.
Results Raise More Questions About the Vaccine
Previous studies have found that the Pfizer-BioNTech vaccine increased immunoglobulin binding to the S1 domain on days 21 and 28 after vaccination. Since the study found a lack of effect in the second vaccine dose, it raises questions about the underlying protective mechanism of the two vaccines.
For example, mRNA vaccines can be potent inducers of innate immunity. SARS-CoV-2-specific secreted IgA has been proposed to be important after natural infection. The effector functions of antibodies can also contribute to protection. A better understanding of potential multifactorial protection mechanisms other than serum antibody or serum neutralizing antibody binding may be important in optimizing vaccination programs, assessing the potential impact of new antigenic variants, and developing new anti-COVID-19 vaccines. generation, ”the researchers write.
The team’s reanalysis also looked at long-term immunity up to day 111, but only after the second dose was given. If a single vaccine can elicit complete immunity, researchers wonder how long the vaccine’s immunity will last.
Potentially, having long-lasting immunity with a single injection would help the vaccine launch and people who have trouble finding or scheduling a second vaccine on a specific day.
Given the number of global cases exceeding 114.7 million and the number of global deaths exceeding 2.5 million, a one-dose vaccine could help expand access to vaccine-induced immunity against SARS-CoV -two.
*Important news
medRxiv publishes preliminary scientific reports that are not peer-reviewed and therefore should not be considered conclusive, guide clinical practice / health-related behavior, or be treated as established information.
