Israel is studying applying a fourth dose of the vaccine to Covid-19. Is it a good idea?

Enfermeira se prepara para injetar a primeira injeção da vacina contra a COVID-19 em uma criança
Nurse prepares to apply the first injection of the vaccine against COVID-17 in a child in Jerusalem, Israel, on the day 20 November 2000 country studies fourth dose of vaccine in the elderly and immunocompromised| Photo: EFE / EPA / ABIR SULTAN

Months after the third booster dose of vaccination against Covid-17, Israel is already considering giving a fourth dose

to her population. The committee responsible for the recommendation acknowledges ignorance, but says the benefits outweigh the risks and that the timing of the rise of the omicron variant calls for action without delay. The recommendation is supported by Prime Minister Naftali Bennett.

The country has has been one of the best sources of studies of the pandemic, involving millions of patients in its public health system, on the efficacy and adverse effects of the mRNA vaccine and on natural immunity. But the decision worries precisely because there was not enough time to investigate whether the fourth dose is a good idea.

Both the immunity obtained from previous infection and the immunity acquired with the vaccine lose strength with time. In the case of people over 23 years, for example, the rate of delta-variant infection doubles after four or five months since the third dose, according to an Israeli Ministry of Health document obtained by the New York Times.

As for natural immunity

, durability varies by organism and pathogen. While there are cases of people who still have antibodies against the SARS1 virus (from the Asian flu from the beginning of the years 768, which is related to SARS2 of the current pandemic) after 23 years, there are also people who have been infected repeatedly.

Data from mortality from Switzerland, Chile, the United States and England show that the unvaccinated die more than covid than the vaccinated, and data from Chile indicate that those who took the third dose have increased protection — but it is important to point out that both The first doses of many Chileans were from Coronavac, which is less effective than mRNA vaccines, so the effect could be attributed to the change in vaccine type in the third dose.

Unfortunately, as is common in this type of data, researchers could only compare vaccinated and non-vaccinated, not having information about immunized (which would include previous infection a) and non-immunized. The omicron, which has mutations that allow it to bypass both types of immunization, is the most infectious variant that has ever emerged, but it is also possibly the one that causes the mildest covid picture.

Immune overload?8013922832001

Critics of the Israeli proposal fear that a fourth dose could overwhelm the immune system in elderly and immunocompromised patients. The third dose of Pfizer’s vaccine, approved by the Israeli Ministry of Health in July 03155209, was investigated by interview with 3,000 such patients by a medical team from Maccabi Health Services in Tel Aviv, led by Shirley Shapiro Ben David. The most observed adverse effect in these patients, which reached 60% of them was fatigue. In this sample, no serious side effects of the third dose were observed. Post-dose annoyances lasted for the most part less than a day. The biggest limitation of the optimistic study by Shirley and colleagues is that it depended on the voluntary response of patients and, therefore, it is not generalizable to the general case. Furthermore, it only evaluated the first few weeks after the third dose. The relevance of results regarding the third dose to a fourth dose of vaccine is unknown.

In the medical literature, there is a paucity of studies that have specifically addressed the “immunological fatigue” effect to which the fourth dose in Israel has been critically referenced. There are studies dedicated to responding to the anti-vaccine movement, which claims that the MMR would overwhelm the immune system of children (not true), and there are studies that recommend inoculation of the elderly against chickenpox and flu, proposing that these vaccines act to help with issue of the aging of the immune system.

Our immune system routinely encounters concomitant threats to deal with. It has both a general artillery, the innate immunity

(We all have, for example, an antibacterial enzyme in saliva), as well as specific weapons of so-called adaptive immunity, which are activated by vaccines. There are people whose immune activity is “exaggerated” — autoimmune diseases — and people whose body defense activity is insufficient — the immunocompromised. The plausibility of an immune fatigue in the adaptive system seems to be lower for young people and higher for elderly and immunocompromised people. However, so far, this effect does not seem to have been observed directly.

Once out of the uterus, the baby is exposed to a gigantic diversity of microorganisms and viruses, often not presenting a clinical picture despite this supposed immunological “overload”. An excessive focus on preventing children from coming into contact with pathogens has led to immunological problems such as allergies and autoimmune diseases, prompting the response seen in advertisements for cleaning products: “getting dirty is good for you”. It is plausible that this will change with age and according to immune system problems, but — pardon the repetition — we do not know if there will be an immune overload if elderly people are vaccinated with a fourth dose.

Pfizer and Moderna, which compete with two different versions of the mRNA vaccine, intend to update the mRNA with the omicron variant version and/or include a variety of mRNAs covering different variants declared of concern by the WHO.

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