Filenews 14 August 2021
The administration of booster doses of vaccines against SARS-CoV-2 is a particularly topical topic of discussion for developed countries that have vaccinated most of their population. The emergence and prevalence of the SARS-CoV-2 "Delta" strain, even in countries with a high level of vaccination coverage, has prompted many countries to launch vaccination programs with additional booster doses. Countries such as Israel, Germany, France, the United Arab Emirates, China and Russia have already started or will begin administering a third booster dose mainly to population groups with weakened immune systems.
Similarly, the U.S. Food and Drug Administration (FDA) recently advocated the administration of a third booster dose to transplant patients diagnosed with malignancies or HIV infection. However, other scientists argue that data on the additional benefit of an additional booster dose is rather insufficient at the moment and regulators should expect further data to be collected before making decisions.
The Doctors of the Therapeutic Clinic of the Medical School of the National and Kapodistrian University of Athens, Theodora Psaltopoulou, Giannis Danasis, Panos Malandrakis and Thanos Dimopoulos (Rector of ekpa) summarize a recent publication in the reputable scientific journal Nature 596, 178-180 (2021). In this context, 5 important questions are raised about the administration of booster doses of the vaccine against SARS-CoV-2:
What is the benefit of administering an additional booster dose of vaccine against SARS-CoV-2?
Administration of a third dose to already vaccinated patients may lead to a faster and stronger immune response against SARS-CoV-2. The results of studies confirming just that have begun and are being published. Third doses of vaccines developed by Moderna, Pfizer – BioNTech, Oxford – AstraZeneca and Sinevac led to an increase in the levels of "neutralizing" antibodies fighting SARS-CoV-2 when administered several months after the second dose. An ongoing clinical trial in the UK will test several combinations of booster doses of vaccines, including the administration of a different type of vaccine compared to the initial vaccination. Preliminary studies of the heterologous vaccination approach show that strong immune responses are released, characterized by high levels of antibodies and T lymphocytes, which have a strong anti-virus effect.
Is immunity from vaccines declining?
To determine the level of immunity, the levels of antibodies after vaccination are usually examined. These usually increase along with the increase in B lymphocytes and then decrease as these cells have a short half-life and decrease. B memory lymphocytes and bone marrow plasma cells continue to create antibodies for decades but at reduced levels. This is the natural course of immunity. From the available data on post-vaccination immunity against SARS-CoV-2 we know that post-vaccination antibody levels decrease over time. However, what has not been clearly defined and is the subject of intensive scientific research is the association of antibody reduction with protection against SARS-CoV-2 infection and severe COVID-19 disease.
Prevents vaccination of COVID-19 infection even after several months;
Since the level of antibody response beyond which COVID-19 protection is reduced has not been determined, we rely on data from observational studies and clinical studies. According to Israel's Ministry of Health, a country with one of the highest vaccination coverage rates in the world, rough data show a drop in vaccine protection from more than 90% at the beginning of the vaccination program to below 50% at the end of June. This may be due both to the prevalence of the "Delta" strain and to the lifting of restrictive measures to prevent the transmission of SARS-CoV-2. Another analysis in Israel showed that those who had been vaccinated in January and February 2021 were 51% more likely to be infected with SARS-CoV-2 than those who had been vaccinated in March and April 2021. It is worth noting, however, that these elements have limitations on the effect of various confounding factors such as the fact that health workers vaccinated as a priority in January 2021 are more likely to be exposed to SARS-CoV-2 and can more easily and more frequently carry out diagnostic tests. Data from randomized clinical studies show that the effectiveness of the Pfizer/BioNTech vaccine has decreased from 96% to 84% after 6 months. Corresponding data for the Moderna vaccine show that the effectiveness of the vaccine has been reduced to 'over 90%' from the original 'over 94%'.
Protect vaccines from severe COVID-19 infection;
It is clear that clinical trial data show that protection against severe COVID-19 disease remains high. Pfizer – BioNTech and Moderna mRNA vaccines show persistent efficacy in severe COVID-19 infection at levels above 90% at 6 months after completion of vaccination with two doses. In addition, data from Israel and the United Kingdom also show that vaccines are extremely effective and those vaccinated with COVID-19 remain out of hospital, even infected with the SARS-CoV-2 Delta strain.
What other factors may influence the decision to administer booster doses of COVID-19 vaccines?
Despite the limited data available on the additional protection that booster doses of vaccines can offer, the advent of the new pandemic wave with the prevalence of the "Delta" strain in many countries around the world puts additional pressure on regulators. Some countries have based their vaccination programme on vaccines based on an inactivated virus, which appear to be less effective at preventing symptomatic COVID-19 infection compared to mRNA-based vaccines and viral vectors such as adenoma. These countries are one of the first to implement booster vaccine administrations. The United Arab Emirates plans to administer a booster dose with Pfizer/BioNTech's mRNA vaccine to those previously vaccinated with the Sinopharm inactivated virus vaccine. China plans to proceed with the production of domestic mRNA vaccines and protein-based vaccines to be administered as booster doses to those previously vaccinated with inactivated virus vaccines. However, there is no clear evidence to suggest that countries that have vaccinated their population with vaccines containing an inactivated virus have worse epidemiological data during the current wave of the COVID-19 pandemic than other countries that have been vaccinated with mRNA vaccines and/or adeno-based vaccines. Despite the limited data available, it is very likely that regulators will act on the role of prevention and approve booster doses of vaccines at least for high-risk population groups for severe COVID-19 disease given that the risk of adverse reactions from vaccination continues to be small and manageable.
