According to an analysis of vaccine effectiveness carried out in Europe, the vaccine effectiveness of the influenza vaccine was moderate in Europe, but good in the population of people over 65 years of age who are the target of vaccination, because the most at risk with the sick.
According to a study byEurosurveillance, the 2017-2018 influenza vaccine had an efficacy of 25 to 52% for all those vaccinated, 53% for children and 36 to 40% for those aged 65 and over.
Study on interim 2017/18 flu VE combined results: Among all ages, VE against any medically attended influenza ranged between 25% (95% confidence interval (CI): −10 to 48) in UK study and 52% (95% CI: 29 to 67) in ES study:https://t.co/tv3BiCo30j
– Eurosurveillance (@Eurosurveillanc) March 3, 2018
In France, where the epidemic is declining very slowly due to bad weather conditions, the first estimates confirm its effectiveness in people over 65.
A partly probabilistic composition
Each year, the influenza virus changes and several viruses can be in circulation at the same time, this proportion can even change according to the country.
Each year, scientists must constitute a “small cocktail” of vaccine strains to try to cover all the viruses in circulation and capable of triggering epidemics.
This composition of the vaccine is partly based on analyzes of what happened in the southern hemisphere for the previous 6 months (during the Southern winter) and on clever probabilistic calculations (the reverse is of course in the case of ‘southern hemisphere).
Trivalent or quadrivalent vaccines
The 2017-2018 campaign vaccines in the northern hemisphere were directed against the A / Michigan / 45/2015 (H1N1) pdm09, A / Hong Kong / 4801/2014 (H3N2) and B / Brisbane / 60/2008 ( line B / Victoria) for the “trivalents”.
The “quadrivalent” vaccines were also directed against the virus B / Phuket / 3073/2013 (line B / Yamagata).
Variable efficacy depending on the strain
In practice, the estimated efficacy of the vaccine was 68% against H1N1 and 36 to 54% against B viruses if we consider them all together.
For the A (H3N2) virus, the vaccine has not been shown to be effective in the general population.
In France, this effectiveness was determined from hospital samples as well as samples in town. Vaccine efficacy in people 65 years of age and over is currently estimated at 57% in an outpatient setting, regardless of the virus, according to networks. Sentinels.
Differences over time and across countries
For European countries, Eurosurveillance reports that 33% of influenza would have been due to an A virus and 41% to a B virus, the majority of infections (50%) were due to an A (H1N1) virus (against 7% for the A (H3N2)) or B from the Yamagata line (38%).
https://t.co/tv3BiCFEoT: #Influenza viruses characterized by clade and study site, Europe, influenza season 2017/18 (n? =? 886) pic.twitter.com/FdGjem0A43
– Eurosurveillance (@Eurosurveillanc) March 4, 2018
In France, after a clear predominance of virus 1 (H1N1) at the start of the epidemic, it is the B virus which has predominated since February.
In the end, the study authors estimated that the efficacy of the 2017-2018 vaccine for the northern hemisphere was good to moderate for virus A (H1N1), moderate for virus B and low for virus A ( H3N2). So pretty good, but could do better for the A (H3N2) virus.
Vaccination remains the best protection against influenza and, above all, against complications and hospitalizations linked to influenza.
.
