Maximum protection against Covid is observed with the so-called ‘hybrid’ immunity, i.e. the one obtained due to the combined effect of vaccination and a previous infection with Sars-Cov-2. This is suggested by a report just published by the Higher Institute of Health (ISS), in which the risk of infection and severe disease is calculated taking into account factors such as previous vaccinations and diagnoses and the time elapsed since the infection or last dose of vaccine. The most protective shield both from contagion with Sars-CoV-2 and from the severe Covid disease is therefore conferred by having had both vaccines and infection. However, it should be noted that a recent vaccination significantly reduces the risks. But let’s see what the report says in detail.
With vaccine and previous infection the risk of serious illness is 80 times lower
Experts point out that the overall risk of infection and severe disease is influenced by both factors, both by vaccination status and by previous infections (documented through a diagnosis). In particular, the risk of severe disease is 80 times greater in those who are not vaccinated and have not had a diagnosis than in those who are vaccinated and have a recent diagnosis. Various significant elements emerge from the report: that in any case, for the same age group and previous infection, vaccination further reduces the risk of severe Covid disease; and, again, that the recent vaccine systematically reduces the risk.
The analysis used data from the integrated Covid surveillance of the ISS, the vaccination registry and the Istat population relating to October 2022, a period in which the Omicron 5 variant (BA.5) was predominant, data that were processed through a statistical model. Based on the results, in all age groups over 12 years, with the same age group and previous infection condition, a reduction in the risk of severe Covid disease associated with vaccination is observed. If, for example, an over 80 person has had a recent diagnosis, the risk of a new severe disease is 100 out of 100,000 if he is not vaccinated, 49 out of 100,000 if he has had a dose for more than 6 months and 42 out of 100,000 if he has had one dose less of 6 months.
It is also observed – the authors of the Iss report point out – a loss of the protective effect against Sars-CoV-2 infection over time, both for previous infection and for vaccination. A decrease in the protective effect of previous infection and vaccination against severe disease is also observed, although this loss is less evident than against infection. The results described, the experts conclude, “confirm the validity of the most recent indications of the Ministry of Health relating to the administration of booster doses”. Updates of the analyzes reported in this document will be published in the extended report of the integrated Covid surveillance system.