Evolution has endowed us with a immune system able to remember. Thanks to this, we do not suffer with the same severity a second infection with the same pathogen and we can develop vaccines. But, as in Salvador Dalí’s work “The persistence of memory“, In which distorted and rotten clocks are shown, the passage of time deforms and vanishes our ability to remember. Perhaps this will allow us to save the energy necessary to deal with new pathogens.
Israel, a pioneer country in vaccination against COVID-19, verified how the incidence of the infection did not stop growing despite having a high percentage of vaccinated population. This was interpreted as a fading of the immunity provided by the Pfizer (Cominarty) vaccine, the majority in that country. As a solution, a third dose was administered to millions of citizens.
In Spain, while the Ministry of Health will offer a additional dose of vaccine in residences, nearly two million people who received a single dose of Johnson & Johnson vaccine (Ad26.COV2.S.) wonder if, over time, they are more vulnerable to COVID-19 compared with the rest.
ONE AND NO MORE?
The vaccine Johnson & Johnson (Janssen) consists of a harmless adenovirus that cannot replicate, but which our immune system recognizes as foreign. The genetic material of the virus carries the instructions that the infected cells translate into a fragment of the S protein (spike) of SARS-CoV-2.
Our lymphocytes recognize this protein as foreign and understand that it is dangerous due to the inflammation caused by adenovirus. Consequently, they will deal with the problem as they do best.
But not all lymphocytes are born equal. Some recognize fragments of the pathogen’s protein made inside an infected cell, killer, cytotoxic or CD8 T lymphocytes. Others use antibodies to fight pathogens when they are outside our cells, B lymphocytes.
The generation of neutralizing antibodies, those that actually prevent the pathogen from infecting its target cell, takes days, and sometimes weeks. After recognizing the antigen, and with the help of the T lymphocytes, the B lymphocyte undergoes a metamorphosis as it divides. Their genetic material changes and a Darwinian selection is produced in which only the best survive, those who produce the most related antibodies for their antigen.
Some B lymphocytes specialize in producing antibodies (plasma cells) that take refuge in the bone marrow, where they die after about two weeks. Others, the memory B lymphocytes, become a backup and sit idle for years waiting to be reunited with their enemy. After the second dose, the memory B lymphocytes, which already have antibodies with high affinity for the antigen, recognize it and rapidly undergo a second metamorphosis. They then divide and differentiate into plasma cells to mature their affinity for the antigen.
Therefore, two doses of vaccine provide us with more lymphocytes than one dose and highly affinity antibodies. However, if after a first dose the antigen remains in our body for a sufficient time, enough neutralizing antibodies can also be produced with good affinity.
On the other hand, a part of the CD8 lymphocytes activated by the vaccine also differentiate into memory cells that wait to find cells infected with the virus. But, unlike B lymphocytes, the genetic material of cytotoxic lymphocytes does not mutate. After a second dose of vaccine, these lymphocytes multiply, increase the number of memory cells, but do not improve their affinity.
THE EFFECTIVENESS OF A DOSE IS MAINTAINED
Data can kill a good story. In clinical trials of the Janssen vaccine, volunteers were vaccinated with one dose (ENSEMBLE trial) or two (ENSEMBLE2 trial, not yet completed). Single dose immunogenicity was very good. This was a great advantage in the face of logistical and production problems that made vaccine administration difficult.
Perhaps because it is a single-dose vaccine, its efficacy in the European population against moderate, severe or critical effects was close to 70 percent, below its competitors based on messenger RNA (Pfizer / Moderna). But perhaps this is because memory lymphocytes remember the adenovirus in the vaccine, reducing its effectiveness.
However, the largest real-world (preliminary) efficacy study (390,500 vaccinated) with a single dose of Janssen conducted in the US has shown 79 percent effectiveness for infections and 81 percent for related hospitalizations. COVID-19.
Most importantly, there was no evidence of reduced effectiveness for the duration of the study, even when the Delta variant was dominant in the US. These data indicate that people vaccinated with a dose of Janssen are sufficiently protected against COVID-19.
Although the preliminary results of the two-dose trial indicate that the amount of neutralizing antibody against the virus increases up to nine times, and despite the recent outbreaks in prisons in our country, which on the other hand seem asymptomatic, it is reasonable to ask whether right now it is necessary and, especially, if it is urgent to give a second dose. Perhaps it is justified in the most vulnerable groups (over 70 years and other vulnerable groups), but not in a general way.