COVID-19 vaccines: November 2020 report
Statement by the Lincei Committee on Covid-19 
Introduction
The hope and hype that the media and public at large are placing on having as soon as possible a vaccine that protects against COVID-19 is the result of the great triumphs that vaccines have had and are having in the control of infectious diseases. However, there is a long series of infectious diseases in which vaccines are only partially effective and we have a series of sensational vaccine defeats.
Indeed, each disease is an immunological problem in itself: even today, with all the data in our possession, it is difficult to predict what kind of vaccine can be truly effective. This difficulty is even greater for COVID-19, a young disease in which ongoing studies in laboratories worldwide are bringing new data. In addition, RNA viruses generally have a high mutation rate. This is one reason why it is difficult to develop effective vaccines to prevent diseases caused by RNA viruses. However, data on the SARS-CoV-2 RNA sequence suggest that this virus does not undergo frequent mutations, thanks to its efficient proofreading system.
In many cases, recovery from a viral disease rests on the combined action of antibodies in the biological fluids that neutralize viral particles and the killer activity of lymphocytes that track down and kill the body's cells infected with the virus. However, there are viral diseases whose healing depends mainly, if not exclusively, on the antibody response and others where the destructive action of the killer lymphocytes is fundamental. What is the case with COVID-19 is not yet defined. First data on T cell reactivity are only recently being published.
Often, healed patients display high titers of SARS-CoV-2 neutralizing antibodies. However, there are also healed patients with a low antibody titer3. Data on the role of secretory IgA and IgM are scarce. Furthermore, we cannot yet know how long the protection acquired by recovered patients lasts. Often the duration of protection after healing somewhat corresponds to the duration of the protection provided by the vaccine.
Despite the impressive amount of studies carried out since the virus was first characterized, there are still a large number of unknowns about this disease. And it is precisely these unknowns that fully justify the very different conceptual and technological strategies that are currently pursued in the preparation of vaccines against COVID-19. This diversification appeared essential precisely because, for many diseases, but mainly in the case of a new disease as COVD-19, it is difficult to predict which type of immune response and therefore vaccine will be more effective.
November 2020
Responsibility for the information and views expressed in this document lies solely with the Covid-19 Committee.
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June 2020