The benefits of using the Oxford / AstraZeneca vaccine greatly outweigh the associated risks. This is affirmed by a team led by the London Mathematical Laboratory (UK) in a study published in the journal Chaos that also shows that the relative benefits are greater in situations in which the number of reproduction is greater and increases with the temporary ban on the vaccine.
In April 2021, the European Medicines Agency (EMA) confirmed that the vaccine of Oxford/AstraZeneca against Covid-19, it could be linked to very rare cases of thrombosis.
This made some countries of the European Union, such as Spain, decided to paralyze the administration of this drug, despite the fact that the EMA insisted that the benefit of vaccination is much greater than the possible harm that this very rare side effect may cause. .
Now this group has explored what consequences this decision would have on the health of the population and on the situation of the pandemic. To do this, they have used an epidemiological model called SEIR with which they have estimated the excess mortality from Covid-19 and possible sequelae in two scenarios: France and Italy.
The main conclusion of the model is that the excess mortality due to the interruption of this vaccine far exceeds the deaths caused by thrombosis, even in the worst scenarios of frequency and severity of the side effects of the drug.
“Our work shows that stopping vaccinations with AstraZeneca for three days, without replacing them with another option, leads to 260 additional deaths in France and 130 in Italy,” says Davide Faranda, lead author of the work. The difference is due to the fact that, as of March 15, 2021, both countries have epidemiological situations and a different reproduction number or R0.
Davide Faranda explained to SINC that the SEIR model assumes that the population can be divided into four groups: those who can contract the virus (susceptible), those infected asymptomatic (exposed), those infected with symptoms (infected) and those who have recovered. “” In this last compartment we not only count those who have overcome the disease, but also the deceased and those vaccinated, “he says.
Through the movements of the model, the excess mortality from Covid-19 and from these side effects related to the vaccine can be estimated
Thus, the model ‘moves’ the population from one compartment to another according to the epidemiological situation, the spread, the time it takes to show symptoms and to be cured of the virus.
Through these movements, the authors write, excess mortality from Covid-19 and these vaccine-related side effects can be estimated.
Due to the large number of uncertainties of these thromboses with thrombocytopenia, for which it is not yet known which groups are most vulnerable or their actual incidence in the vaccinated population, the researchers calculated the worst-case scenario and assumed that these side effects would have higher associated mortality than currently reported.
The model interprets that, if vaccination is resumed at the same rate as before the interruption, there will continue to be excess mortality: This is a clear result of the non-linear effects of epidemiological dynamics, they write: those who have not been vaccinated can infect other individuals before vaccination is resumed.
In other words, the researchers note: “a few unvaccinated individuals can produce a large number of infected individuals. The process can only be stopped if a large number of daily vaccinations are carried out. ‘
Furthermore, even if the campaign was resumed with double the doses injected during the same number of days of the break, the excess mortality would continue in the coming days, although with somewhat lower figures than in the standard restart.
The report shows that the effects of the disruption are difficult to counteract and would continue over time. To all this is added that public confidence in vaccines will decline, something that directly affects public health but that this study does not include.
In this sense, they acknowledge that the “estimates are conservative and possibly underestimate the excess deaths derived from disbelief in vaccination policies observed in the largest European countries. The analysis presented here has been performed with a thorough but well thought out and tested model, and we hope that the results will be the starting point for more detailed, more advanced and mature investigations with sophisticated models and data collection exercises. ‘
Faranda acknowledges to SINC that this mathematical interpretation has several strong limitations: the model assumes that there is only one vaccine with the Oxford / AstraZeneca characteristics and forgets the rest of the options approved in Europe and does not include age as a risk factor. something that the EMA is evaluating in the case of side effects related to this vaccine.