Viruses are microorganisms with relatively simple structures, basically composed of proteins and genetic information. This characteristic makes them have a high mutation capacity.
With the coronavirus it is no different. The extensive circulation of the virus that causes Covid-19 contributes to the emergence of new variants. Since the discovery of Ômicron in November 2021, the coronavirus has continued to evolve, giving rise to many descendant and also recombinant lineages.
According to the World Health Organization (WHO), which continuously monitors the different strains, the genetic diversification of Ômicron indicates a pressure on the virus to adapt to human hosts.
Most viral mutations are located in the Spike protein, used by the virus to invade human cells. Some of these mutations can make the virus less susceptible to the immune response expected by vaccines.
The vaccines against Covid-19 in use around the world were developed from the strains of the virus that circulated at the beginning of the pandemic and that did not have the same amount of mutations as the circulating strains at the time.
However, ongoing studies indicate that even in the face of mutations, immunizers remain effective in protecting against serious conditions, hospitalizations and death from the disease. The analyzes also indicate that the booster dose significantly increases the level of protection against infection, which tends to decrease after six months.
What contributes to the maintenance of protection
The immunologist Cristina Bonorino, a professor at the Federal University of Health Sciences of Porto Alegre (UFCSPA), explains some of the factors that contribute to maintaining the effectiveness of vaccines in use.
According to the specialist, the effectiveness of vaccines is related to the production of specific neutralizing antibodies against the coronavirus and the induction of other mechanisms related to the body’s defense, such as the activation of lymphocytes, or T cells.
The so-called cellular response generated by immunizers involves memory cells of the immune system that remain in the body. Thus, when the individual comes into contact with the coronavirus through a natural infection, they activate the production of antibodies that respond against the infection, mainly preventing the worsening of the disease.
“There are two types of immune protection against viruses that generate memory. One of these are antibodies, the other is T lymphocytes, which are in the tissues, lungs and other organs, protecting the disease. This immunity was not affected by the variants in any way as far as we were able to measure”, says Cristina.
As most of the mutations are found in the Spike protein, the main impacts reflect mainly on the ability of the virus to invade human cells, and not on the worsening of the disease.
“Most of the mutations are in the part of the Spike protein we call RBD, which is the part that binds in the receptor. Omicron mutations are mostly there. If you look at, say, T lymphocytes, the mutations don’t affect the areas that they recognize. Because they recognize very small pieces”, explains the immunologist.
Researchers at Imperial College, London, carried out a large study that supports the importance of vaccination. Although the human body is able to produce defenses against the coronavirus during natural infection, the level of protection may not be that high depending on the variant involved, according to the research.
In the British study, which included the participation of health professionals, researchers investigated T and B cell immunity against Omicron in vaccinates with different histories of SARS-CoV-2 infection.
The results of the study, published in the journal Sciencepointed out that the Ômicron infection was not able to reinforce the mechanisms of action of the immune system.
What the effectiveness studies say
Unlike efficacy trials, which pertain to studies conducted in controlled environments, such as those conducted during vaccine development, effectiveness data reflect the results of vaccination in practice in large populations.
At least 33 studies from 14 countries (Argentina, Brazil, Canada, Chile, Czech Republic, Denmark, Finland, Norway, Israel, Qatar, South Africa, United Kingdom, United States and Zambia) have broadly evaluated the protection of six vaccines against Covid-19 in the face of infection by the Ômicron variant.
Among the surveys, 12 studies contributed with estimates of effectiveness only for the primary vaccination schedule, four presented data only for the first booster dose, and 17 contributed for both.
The results of these studies show reduced effectiveness of vaccines against the Ômicron variant, with only the primary series, for all outcomes (severe illness, symptomatic illness and infection) compared to what was observed for the other four variants of concern of the coronavirus: Alpha, Beta, Gamma and Delta.
However, estimates of effectiveness against Ômicron remain higher for severe disease than other clinical conditions in most studies. The analyzes also show that the first booster dose significantly improves vaccine effectiveness for all clinical outcomes.
The results of the studies indicate that, after the first booster dose, the effectiveness of vaccines decreases more for symptomatic disease and infection than for severe disease over time. However, studies evaluating the effectiveness of booster vaccination over a period longer than six months are not yet available.
For severe disease, the effectiveness of the primary vaccination schedule showed little decline over six months.
The rate was greater than or equal to 70% during the first three months after vaccination for 7 of 13 (54%) effectiveness estimates for Pfizer and Moderna’s messenger RNA vaccines.
Of the two available viral vector vaccine studies, both had less than 70% effectiveness: one reported less than 70% effectiveness for AstraZeneca and the other indicated less than 50% effectiveness for Janssen. Regarding inactivated virus vaccines, estimates indicate that Coronavac presented effectiveness greater than or equal to 50%.
New generation of vaccines
For the experts consulted by the CNN the development of a new generation of vaccines against Covid-19 is an expected move by the pharmaceutical industry in search of improvement – which does not necessarily mean that the immunizers in use have lost their ability to protect.
Considering the viral evolution over time, the update of vaccines will allow the development of formulations with more comprehensive protection, capable of reducing even the infection more robustly, and also for a longer period, as with other types of immunizers.
“The immunity that the variants affected was the ability of the antibody to prevent the virus from entering the cell. So even if he gets in, you’ll still be protected. Up-to-date vaccines will decrease the chance of him getting in”, says Cristina.
Pfizer and Moderna, pharmaceutical companies that use messenger RNA technology against Covid-19, presented results of specific vaccine candidates for the Ômicron variant.
In June, Pfizer released promising data on the adapted version of two vaccines, one monovalent and one bivalent. While one is a combination of Pfizer’s vaccine, the other is targeted at the Spike protein of the BA.1 lineage of Ômicron.
According to Pfizer, data from the Phase 2 and 3 study indicated that a booster dose of both adapted vaccine candidates elicited a substantially greater immune response against BA.1 from Omicron BA.1 compared to the current vaccine. Robust immune response was observed at two dose levels of 30 and 60 micrograms.
On July 8, Moderna presented new clinical data on the messenger RNA vaccine targeting the Ômicron variant. Results show expressive antibody responses compared to the current booster dose. The booster dose of 50 micrograms showed a safety profile in the study that involved 437 volunteers.
booster dose
The first booster dose improved protection against severe illness in all studies. The effectiveness of the vaccine was equal to or greater than 70% in 94% of the estimates that evaluated protection between 14 days and three months after receiving the booster.
Three to six months after booster with messenger RNA vaccines, the rate was equal to or greater than 70% for 21 of 26 estimates.
Considering only the initial vaccination schedule, the effectiveness of immunizers against symptomatic infection in the first three months was lower compared to severe disease. Furthermore, effectiveness declined more significantly over time.
“Vaccines decrease protection over time and according to the variant that is circulating, but when we apply boosters, both the first and second boosters for those who are already indicated, it restores this protection. For Ômicron, this booster dose is essential”, says Juarez Cunha, president of the Brazilian Society of Immunizations (SBIm).
Studies show that booster dose of messenger RNA vaccines after completion of a primary series of a vaccine of the same type, AstraZeneca or Coronavac, improved protection against symptomatic disease.
However, the protection of the first booster dose rapidly diminished over time: only three of the 13 estimates available at three to six months after receiving a booster dose had an effectiveness greater than or equal to 50%, and none were equal to or greater than 50%. greater than 70%.
“With complete vaccination, which takes into account when people even have boosters, the possibility of having serious illness, hospitalization and death is much lower compared to those who only had the basic two-dose vaccination or to those who did not get vaccinated. ”, says Cunha.
Source: CNN Brasil
