The flu vaccine reduces mortality from this disease by half, especially in people over 65 years of age, although it cannot always prevent the disease. This is the main conclusion of a Spanish study published in the journal European Respiratory Review, which analyzes data on the effectiveness of vaccination against influenza more than 38 countries and 6.5 million patients.
The research, carried out by the CEU San Pablo University with the collaboration of the Carlos III Health Institute (ISCIII), concludes that preventing infection may not be the main benefit of vaccines, but it does reduce the associated complications.
As the authors explain, many studies quantify the effectiveness of the vaccine by calculating the probability of infection of vaccinated versus unvaccinated people. However, in this research other parameters have been used, such as calculating how much serious cases are prevented, hospital admissions, the probability of being admitted to the ICU, and the probability of dying.
“We have quantified the protection against infection, and what we see is that the vaccine, especially in the case of the H3N2 subtype, is usually not very effective in protecting against infection, especially in older people. But, in regards to protect against hospitalization and death, is highly effective“says Estanislao Nistal, lead author of the study. “The message is that, whether or not they work to prevent infection, vaccines against all influenza viruses that infect humans are effective in preventing the worsening of the disease.” he insists.
Variations according to age
In fact, the effectiveness of infection varies depending on age. For example, usually avoid infections against the H1N1 subtype of the influenza A virus and against the influenza B virus in all age groups, from children under five years of age to people over 65. However, the vaccine protects less against infection in adults compared to another subtype of influenza A, H3N2. .
In addition, the study also marks another milestone related to the risk factors that worsen the course of this virus. “Cardiovascular and neurodegenerative diseases are the main factors associated with deaths caused by the flu, but, when these people are vaccinated, the risk of dying is reduced by three or even four“, declared the leader of the study.
The meta-analysis that these researchers have developed included 192,705 patients to collect data on the incidence and severity of influenza, as well as the impact of annual vaccination, subsequently validating their findings with an additional sample of more than 6.5 million patients from the TriNetX database.
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