Vaccines also affect the circulation of Covid: ideas for the government

Literature reviews, when updated, are particularly useful for taking stock of what we know about a given topic, and in some cases can help to better understand slippery and dangerous claims, such as those made by the Minister of Health Horace Schillaci, who in an interview with Libero yesterday recommended the fourth dose against Covid-19 only to the frail and not to others and then stated that he saw no reason to be in favor of compulsory vaccination. We advise Schillaci to examine an article published on December 2 in Nature Reviews Microbiology dedicated to the data we have on the measurable viral load after SARS-CoV-2 infection and on the recovery of infectious virus from infected subjects: these are, in fact, two of the most important parameters that influence the ability of a virus to propagate in a population.

Let’s focus on the data presented for Omicron. First of all, it is reiterated that vaccination, and especially a recent booster dose, substantially decreases the chances of serious consequences of the infection. As regards the amount of viral RNA recoverable in Omicron-infected subjects, no differences were found, whatever the vaccine dose, with the non-vaccinated, both for BA.1 and for BA.2. Furthermore, the length of time within which it is possible to recover infectious viral particles is equally indifferent to the vaccination status, as is the fraction of infected patients from which such particles are recovered.

However, the review highlights an important point: after Omicron infection, those who received at least one booster dose show a reduced total amount of infectious virus 5 days after the first symptoms. Therefore, even if in vitro infectious virus is recovered regardless of the vaccination status, the amount that is found is different. Since then, despite what is said in Italy in the political rooms, the infectivity window reaches 10 days after the symptoms, the 5-day data shows that those who have taken at least one booster dose are potentially less infectious the same time elapsed from the onset of symptoms.

Now we already know that the protection from infection conferred by a booster dose of current vaccines, against Omicron, is nothing, even if it expires after two months. This means that, by carefully modulating the recall times with respect to the epidemic waves, the maximum effect is obtained on viral circulation, both in terms of infection and in terms of transmission, as we have seen for the five-day figure.

Furthermore, the five-day quarantine for the infected, even on the basis of the latest available revision, is insufficient if the aim is to hinder viral circulation as much as possible. In conclusion, therefore, there is still a limited infection and transmission prevention effect of the available vaccines, together with a demonstrable effect of an isolation longer than five days. It is therefore a question of temporally calibrating public health interventions, also taking into account this latest revision; provided, on the other hand, that it is not decided to let SARS-CoV-2 circulate freely, assuming the responsibility for hospitalizations and preventable deaths on the increase.