In Israel the third dose has been administered for some time and reminders are discussed every 6 months to renew the Green pass. In Italy everything is ready for the third and we will start with the immunosuppressed. To better understand the vaccination strategy Ilfattoquotidiano.it interviewed Lorenzo Moretta, director of the Immunology Department of the IRCCS Bambino Gesù in Rome, one of the most authoritative scientists on the subject.
In Israel six-monthly recalls are envisaged. From 1 October those who have only two doses of the vaccine will be considered as unvaccinated, for the purpose of the vaccination certificate. What do you expect from the future?
It seems to me an excessive measure for the general population. It is understandable for healthcare professionals and frail patients.
The decision on vaccine boosters is based on the antibody titer (number of antibodies detectable by serological), so is there a “number” that ensures protection from Covid?
There is no standard level. Currently, the antibody titer is an easily measurable parameter. But I stress that both natural infection and vaccination induce “memory cells”: B cells, plasma cells and helper and killer T cells that are not measured (except in specialized research centers). For example, there may be a very low antibody titer, but if you have “memory cells” they quickly produce many antibodies against the virus for which, in fact, you are immune and you are unlikely to get seriously ill following a new contagion.
Yet is the third dose of the vaccine scheduled because the antibodies “drop” after 4-5 months?
As I said there is no standard level, a number of antibodies that defines the safe protection from the virus. The number of antibodies are a kind of spy, important. But if you have “memory” cells, which are not currently measured, it prevents the virus from causing serious infections.
A study published by Nature has shown that B cells (of the immune memory, present in our marrow and lymph nodes) protect for long periods, even years. The study referred to both natural (recovered) and vaccine-induced immunity. So what is the choice of a third dose based on?
To date, the third dose is indicated above all for healthcare personnel and for fragile subjects: it is an extra lifesaver, which induces a rapid and abundant production of antibodies. In fact, many circulating antibodies prevent the virus from attaching to our cells, infecting them and replicating. If this happens, then we find it in the mucous secretions, especially of the nose. And this is a danger when it comes to healthcare personnel who can infect patients.
If a person has high antibodies should they do the same third dose?
In this case the third dose may not be strictly necessary or at least it could be postponed and used for those with few antibodies. However, given that the first to receive it will be the immunocompromised and then the elderly of the RSA who, on average, respond less to vaccines, so far everything is fine. Then, I think it will be decided based on the availability of the vaccine (and this does not seem to be a problem) and, above all, on the possibility of measuring antibodies on a large scale. I believe that healthcare professionals should receive the third dose to minimize the possibility of infecting patients.
According to a recent US study not yet reviewed on Medrxiv, it has been seen that vaccinated and non-vaccinated people have a comparable ability to infect others. Vaccines would serve for two reasons: to protect themselves and to block infections for the community
These are data relating to the Delta variant. There may be the presence of viruses in the upper airways even in infected vaccinates, both asymptomatic and with mild symptoms. Since it may be due to the time it takes for the memory cells to intervene and stop the infection. These data once again underline the importance that even vaccinated people maintain the use of masks and respect the physical distance in order not to spread the infection.
Vaccinated people have 13 times more risk of being infected with Delta than Covid “cured” according to a recent Israeli study
The Delta variant is mutated in the Spike receptor (against which the vaccine is directed). Those recovered from natural infection have made antibodies and have memory cells against other components of the virus as well. Therefore, the antibodies of the vaccinated may be less effective against the mutated Spike, while in the recovered the greater protection is guaranteed by antibodies against all the viral components. The vaccination of the recovered is navigated “on sight”, based on the data collected progressively and this also applies to the statistical aspects. We’ll see. It may be that in the future vaccination with a killed or attenuated virus is preferred, which would give immunity more similar to that conferred by natural infection.
So the “recovered” from Covid are more protected than the “vaccinated”?
Natural infection leads to an immune response against various parts of the Sars Cov 2 virus, so it can give you more protection. The vaccine, on the other hand, is built to target the spike receptor, which is crucial for infecting cells. Hence, all antibodies are directed against that single molecule. So protection can be better in the healed. Then, there are notable individual variations in the immune response.
If a variant pierced the vaccines and thus had a competitive advantage (over other mutations, Delta has part of this advantage) in the vaccine group, what would happen?
If a variant develops that increases the lethality of the virus then that would be a real problem. A serious problem for everyone, including the vaccinated. In this case it would be essential to recognize the variant and to prepare tailor-made vaccines as soon as possible. But I’ll make an important note: viruses select variants over time that increase their transmissibility. Then, in a much longer timeframe, a virus could reduce its lethality, or so viruses in nature have taught us so far. In fact, selecting a strain that kills the host (us) is not beneficial to the virus itself.
The Green pass after a dose, if not accompanied by distances and FFP2 masks, may not be enough?
A single dose of vaccine protects little and the Green pass can give the illusion of safety and favor the increase of infections, especially if the spacing and use of masks is not respected. But it must be said that it is a very important incentive to get people vaccinated. I repeat that everyone must understand that it is essential to maintain masks (FFP2) and distances, even with the Green pass.
The study in Nature
The Medrxiv study