A report by Public Health England has unveiled that last winter's flu jab worked in 34% of cases. In the case of children under 18 years of age, it offered protect at 35% against the strains of influenza A.

Professor Paul Cosford, PHE's director for health protection and medical director, said, that in past few years, they have seen the vaccine to be around 50% effective in the UK. But last year, they have witnessed a little efficacy than usual with regard to vaccine.

"Whilst it's not possible to fully predict the strains that will circulate in any given season, flu vaccination remains the best protection we have against an unpredictable virus which can cause severe illness and deaths each year among at-risk group", said Cosford. At risk groups include elderly, pregnant women and the ones having a health condition.

As per a research, child's flu vaccine is 100% effective against influenza B. In the case of adult vaccines, the efficacy level varies between 29.3% and 46.3% against A and B strains. Generally, a flu vaccine works in 50 out of every 100 cases.

But experts affirmed that one strain has mutated so significantly that the vaccine offered much lower levels of protection. The strain that is bothering is H3N2 as it primarily kills the elderly.