Coronavirus - Do we need to get a third dose of the vaccine? - Experts answer five "hot" questions

Commemorative doses of SARS-CoV-2 vaccines are a very topical issue for developed countries that have vaccinated most of their population.

The emergence and dominance of the SARS-CoV-2 Delta strain, even in countries with a high level of vaccination coverage, has prompted many countries to start vaccination programs with additional booster doses. Countries such as Israel, Germany, France, the United Arab Emirates, China and Russia have already started or will start giving a third booster dose mainly to populations with weakened immune systems.

Similarly, the US Food and Drug Administration (FDA) recently advocated giving a third booster dose to transplant patients, patients diagnosed with malignancies or HIV infection. However, other scientists argue that data on the additional benefit of an extra booster dose are rather inadequate at present, 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 relevant recent publication in the prestigious scientific journal Nature 596, 178-180 (2021).

In this context, they are set 5 important questions for booster of SARS-CoV-2 vaccine:

What is the benefit of receiving an extra booster dose of SARS-CoV-2 vaccine?

Administration of a third dose to those already vaccinated may result in a faster and stronger immune response to SARS-CoV-2. The results of studies that confirm exactly this have started and are being published. Third doses of vaccines developed by Moderna, Pfizer - BioNTech, Oxford - AstraZeneca and Sinovac led to an increase in the levels of "neutralizing" antibodies that fight SARS-CoV-2, when administered several months after the second dose.

An ongoing clinical trial in the United Kingdom will test different combinations of booster vaccine doses, including different types of vaccine compared to the original vaccine. 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 strong antiviral activity.

Is immunity declining from vaccines?

To determine the level of immunity, titers or antibody levels are usually tested after vaccination. 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 make antibodies for decades but at reduced levels. This is the natural course of immunity.

From the available data on post-vaccination immunity to SARS-CoV-2 we know that antibody levels after vaccination decrease over time. However, what is not 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 disease. COVID-19.

Vaccination prevents infection COVID-19 even after several months?

As the level of antibody response beyond which protection against COVID-19, we rely on data from observational studies and clinical trials. According to the Israeli 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 over 90% at the beginning of the vaccination program to less than 50% in end of June. This may be due to both the prevalence of the Delta strain and the lifting of restrictive measures to prevent the transmission of SARS-CoV-2.

Another analysis in Israel showed that those vaccinated in January and February 2021 were 51% more likely to be infected with SARS-CoV-2 than those vaccinated in March and April 2021. However, it is worth noting that these data have limitations on the effect of various confusing factors such as the fact that primary care vaccinators in January 2021 are more likely to be exposed to SARS-CoV-2 and can more easily and frequently perform diagnostic tests. Data from randomized clinical trials 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%".

Vaccines protect against serious infection COVID-19;

It is clear that clinical trial data show that protection against serious disease COVID-19 remains high. Pfizer - BioNTech and Moderna mRNA vaccines show persistent efficacy in severe infection COVID-19 at levels above 90% at 6 months after completion of the two-dose vaccination. In addition, data from Israel and the United Kingdom also show that vaccines are extremely effective and that vaccinated 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? COVID-19;

Despite the limited data available on the additional protection that booster doses can provide, the advent of a new wave of pandemic with the Delta strain prevailing in many countries around the world is putting additional pressure on regulators. . Some countries have based their vaccination program on inactivated virus-based vaccines, which appear to be less effective in preventing symptomatic infection. COVID-19 compared to mRNA-based vaccines and viral vectors such as adenoids. These countries are among the first to implement booster vaccinations.

The United Arab Emirates plans to give a booster dose of the Pfizer / BioNTech mRNA vaccine to those who have previously been vaccinated with the Sinopharm Inactivated Virus Vaccine. China plans to produce domestic mRNA vaccines and protein-based vaccines to be given as booster doses to those who have previously been vaccinated with inactivated virus vaccines. However, there is no clear evidence that countries that have vaccinated their populations with inactivated virus vaccines are experiencing worse epidemiological data during the current pandemic wave. COVID-19 compared to other countries that have been vaccinated with mRNA vaccines and / or adenosine-based vaccines.

Despite the limited data available, regulators are more likely to act on the role of prevention and to approve booster doses of vaccines, at least for high-risk populations. COVID-19 given that the risk of side effects from vaccination remains small and manageable.

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