Vaccines, what (and why) has changed. Timing, age, recall rules

Different drugs for age groups. How does the administration work now?

The vaccination campaign against Covid-19 can count on four products, all authorized first by the European Medicines Agency (Ema) and then by the Italian Medicines Agency (Aifa). Two are mRna vaccines, an innovative mechanism of action: one produced by Pfizer-BioNtech (Comirnaty) and one by Moderna. The first was authorized in the European Union on 21 December 2020 by Ema and the day after by Aifa. It is indicated for adults and adolescents from 12 years of age. The second on 6 January by the EMA and on 7 January by Aifa. It is suitable for adults from 18 years of age. For both of these vaccines, maximum efficacy is achieved after administration of the second dose. Two others are adenoviral vector vaccines: in the AstraZeneca product (Vaxzevria) it is a chimpanzee adenovirus; in Johnson & Johnson (Janssen) of a human adenovirus. The first was authorized by the EMA on 29 January and by Aifa on 30 January. Since yesterday its administration is indicated in adults over 60 years of age. Two doses are provided to achieve maximum immunizing efficacy. The second viral vector vaccine was authorized by the EMA on 11 March and by Aifa the day after. Administered in a single dose, it is authorized for adults from 18 years of age, but the Ministry of Health recommends its preferential use for those over 60.

The CTS recommends that even for the open days organized by the Regions, the age guidelines just issued should be respected, limiting AstraZeneca to over 60s.

The second dose with the same vaccine or with a different one? What the CTS decided and what science says

After blocking the administration of AstraZeneca to those under the age of 60, the Technical-Scientific Committee (CTS) for an attitude of extreme caution – although no cases of thrombosis have been recorded in Italy after the second dose of this vaccine – recommended to also give the second dose of AstraZeneca only to people over 60. Completing the vaccination process with another product (“heterologous vaccination”) affects approximately 900,000 people under 60 who received the first dose of AstraZeneca. The circular from the Ministry of Health prescribes to administer the second dose with an mRna vaccine (Pfizer or Moderna) at a distance of between 8 and 12 weeks from the first dose. The CTS – it is explained again in the circular of the ministry – observes that although no studies have been published that include a large number of subjects; nor are there any randomized studies in which the control arm is represented by two administrations of the AstraZeneca vaccine “it can be said, on the basis of the available evidence, that the described” heterologous “vaccination finds its solid immunological and biological rationale and not appears to be inadvisable neither on the safety front (reactogenicity), nor on that of immunogenicity ». The data currently available deriving from studies conducted in various European countries – adds the CTS – indicate “the ability of this approach to induce a good antibody response and an overall acceptable reactogenicity profile and not dissimilar to that observed by administering two doses of the same type of vaccine”.

Why has AstraZeneca been limited to people over 60?

The Technical-Scientific Committee (CTS) has recommended limiting the use of the AstraZeneca vaccine (chimpanzee adenoviral vector vaccine) to those who are 60 years of age or older because the best epidemiological picture is the lowest circulation of the Sars-CoV-2 virus in our country changes the risk-benefit ratio. The potential risks of thrombosis in unusual locations (cerebral venous sinuses, arteries, district of the large abdominal vessels) associated with thrombocytopenia had already been addressed by the CTS last May 12 based on an EMA analysis of April 23, but at epoch the viral circulation was framed in an intermediate scenario. Now, in the light of the changed epidemiological context and of “some recent adverse events chronologically – reports the circular of the Ministry of Health – and, probably, also etiologically, linked to the administration of this type of vaccine”, the CTS has evaluated to modify the indications . Also in light of the prevalent availability of mRna vaccines (Pfizer and Moderna), the Technical-Scientific Committee has decided to strengthen the recommendation for the use of the first dose of the AstraZeneca vaccine in subjects over 60 years of age, in whom the benefit resulting from vaccination overcomes the potential risks associated with the development of thrombosis phenomena associated with vaccination.

Johnson is also a viral vector vaccine. Why can it still be given to under 60s?

The Johnson & Johnson vaccine is an adenoviral vector, similar to the AstraZeneca product and is authorized for adults over 18 years of age: the Ministry of Health has recommended its preferential use over the age of 60, but has not prohibited it below this age threshold. In the United States, after an initial suspension, the Centers for Disease Control and Prevention (CDC) had proposed to resume administering this vaccine, but proposing a warning for women under 50, for the occurrence of some adverse events in this vaccine. segment of the population that made the risk-benefit ratio unfavorable. While taking into account the similarities between AstraZeneca and Johnson products, explains the CTS, “the current state of knowledge, the number of just over a million doses administered in the country today and the rarity, even in Europe, of reports of thrombosis in available today, do not allow to draw conclusive assessments with respect to the benefit / risk ratio “relative to the Johnson vaccine. With the advantage of being effective in a single dose, which makes it useful for certain categories of the population, the Johnson & Johnson product is recommended for people over 60, but not prohibited under that age.

Population immunity. When will we reach it?

The vaccination campaign designed by the Covid-19 emergency commissioner, General Francesco Paolo Figliuolo, expects to reach 80 percent of the Italian population immunized by the end of September. The goal is based on the possibility of carrying out at least 500 thousand inoculations per day – a figure increasingly reached and exceeded in recent weeks – and of guaranteeing a constant supply of vaccines, according to the centralized purchasing and distribution plan by the European Union. Even if the EU itself has started a dispute with AstraZeneca – accusing it of delays and contractual breaches – and has therefore interrupted the further supply of vaccines from this pharmaceutical company, Italy remains – between doses already at home and others still to be received – about 15 million doses of this vaccine. On Friday, Commissioner Figliuolo did not hide that this stop at AstraZeneca for the under 60s will have some “minimal impact” on the plan, which could translate into delays in the administration. His hope, however, is to be able to recover them by July-August, to finish the campaign regularly in September. However, for the objective to be achieved, it will be necessary that there is no crisis of distrust towards the AstraZeneca vaccine in the population that can receive it. And that the same problems as for AstraZeneca do not occur for the Johnson & Johnson vaccine.

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