How does the AstraZeneca vaccine work?
The Oxford-AstraZeneca vaccine, recently renamed Vaxzevria a viral vector vaccine, uses an incapable of replicating virus (a chimpanzee adenovirus) that delivers the genetic code of the SARS-CoV-2 Spike protein to human cells against which our immune system is activated. a very manageable vaccine that can be stored at 2-8 degrees for six months and has a low cost, less than three euros.
What are the efficacy data on the adult population and on the elderly?
According to the latest data, released on Thursday 25 March, the AstraZeneca vaccine has an efficacy of 76% on the general population (with a confidence interval ranging from 68% to 82%). In adults 65 years of age and older, 85% efficacy (with a confidence interval of 58% to 95%). The drug has been shown to prevent serious illness, hospitalization and death by 100%.
Where used?
At the end of March, the AstraZeneca vaccine received authorization in over 80 countries but was expected in around 140 countries: in fact one of the key vaccines provided by COVAX, the global vaccine facility that aims to reach middle and low income countries .
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Who do you recommend?
There was a ballet of figures on the age groups to use the vaccine. The European Medicines Agency (EMA) at the end of January approved AstraZeneca aged 18 and over, but at first some countries (including Germany and Italy) had chosen to allocate it to people under 55 because there was a lack of data on the effectiveness in the elderly population, which is why in our country it was initially intended for the teaching staff and the police forces. When the data arrived, and they were favorable, the use was liberalized for every age group from 18 years upwards. Recently the recommendation in some countries has gone in the opposite direction: it was decided to limit its use only to subjects over 55-60 years of age.
What problems have led to this change of destination?
Some cases of a very rare particular type of thrombosis (with widespread blood clots and a low platelet count, sometimes associated with bleeding) reported mainly in women aged 25 to 65 years. In Great Britain there have been 30 people out of 18 million vaccinated (with 7 deaths), in Germany 31 cases, in the Netherlands 5, in France 12: the unusual combination of symptoms has so far been detected in at least seven countries with highly variable incidence estimates . The latest report in Italy concerns a 32-year-old teacher hospitalized in Liguria with a cerebral hemorrhagic thrombotic picture.
Who has limited its use in relation to age?
Germany, France, the Netherlands, Sweden, Iceland, Finland and Canada have decided to limit the use of the vaccine to elderly people only (generally over 60). The Netherlands has suspended its use entirely to avoid waste and reorganize the vaccination campaign in the meantime. Thailand and Indonesia have temporarily suspended their use. The Democratic Republic of Congo and Cameroon have decided, for now, not to use it.
Is there a causal link between rare thrombosis and the AstraZeneca vaccine?
EMA’s risk assessment committee has already reviewed the issue and data on thrombosis and reiterated that, to date, there is no evidence to suggest the exclusion of certain age groups from drug administration. The vaccine was found to be safe and there are no causal links between the reported adverse effects and the drug. The EMA, however, has not even ruled out that there may be a link and continues the investigation. The data on the incidence of this type of thrombosis could be staggered due to the type of population vaccinated: many countries, in fact, have used AstraZeneca on people under 65 and groups such as health professionals and teachers, the majority of which are women.
What is the risk-benefit calculation by age group?
What emerges is that the people who develop the thrombotic problem are of such age that they probably would not die if they fell ill with Covid-19, while half of the thrombotic events linked to a low platelet level fatal, explains immunologist Sergio Abrignani, Professor of General Pathology at the University of Milan. While in the over 55s the benefit of the vaccine is enormously greater than the risk of thrombosis, in the younger population the figure deserves further reflection on the risk-benefit ratio, also because we have different vaccines to choose from.
Is it possible to use another vaccine for the second dose?
In Germany, plans are being made to complete the vaccination of under-60s who received the first dose of AstraZeneca with a second dose of an mRNA vaccine (Pfizer or Moderna), a decision that could affect 2.2 million Germans. According to Sergio Abrignani, one thing that makes sense, because it can work immunologically. I am sure that using one of the other two RNA vaccines approved in Europe for the second dose after the first dose with AstraZeneca will work because it induces a strong immune response. However, specific Phase 3 trials are needed on this procedure that are not yet available.
What are the ideal timing between the first and second dose?
Currently, the World Health Organization is instructed to provide the second dose of AstraZeneca within 8 to 12 weeks. At the moment in Italy, also given the shortage of vaccines, the booster with AstraZeneca is expected 3 months after the first administration.
Does it work against variants?
A preliminary analysis in a UK study found that AstraZeneca provides a level of protection similar to the standard one against the English variant (B.1.1.7), the one prevalent (90%) in our country. There are insufficient data on the Brazilian variant, while the efficacy against the South African variant has had very low percentages, so much so that South Africa has suspended the diffusion of the AstraZeneca vaccine, although the WHO still recommends its use for protection from severe illness.
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