Flu season has just hits its peak in 2014 - the number of deaths related to flu infections have reached epidemic threshold, according to a report from the Centers for Disease Control and Prevention, with fifteen child deaths so far. One possible reason for this is a less effective flu vaccine against new mutations in 2014.

The Huffington Post reports that 6.8 percent of all deaths reported during the 51st week of the year (ending Dec. 20) were related to pneumonia and influenza. Four of those fatalities were pediatric patients, which makes a total of 15 pediatric deaths related to the flu so far for the 2014-2015 flu season beginning Oct. 1, according to the authors of the CDC report. A pediatric death means a person who lives in the U.S. and is younger than 18.

A possible reason for the high number of pediatric deaths this year is that the flu vaccine administered in 2014 was not very effective against new mutations in this year's flu strain:

CDC director Tom Frieden addressed the issue Dec. 4 in a press conference: "We know that in seasons when H3 viruses predominant, we tend to have seasons that are the worst flu years, with more hospitalizations from flu and more deaths from the flu. Unfortunately, about half of the H3N2 viruses that we've analyzed this season are different from the H3N2 virus that's included in this year's flu vaccine. They are different enough that we're concerned that protection from vaccinations against these drifted H3N2 viruses may be lower than we usually see."

However, Frieden emphasized that the flu vaccine is still the best way to protect against illness, even if the flu shot effectiveness might be lower than expected.

In 2013 around this time there had been four child deaths and in 2012 that number reached 16, according to Michael Jhung, medical officer for the CDC, USA Today reports.