Each winter, people are strongly encouraged to get vaccinated against the flu. But this year's version of the vaccine may not be as effective as in most years.
This year's flu vaccine does not protect well against a specific H3N2 strain of flu that has been seen most often this year. Worse, it is a strain being seen that tends to cause more hospitalizations and deaths. However, this year's vaccine provides some protection. The Centers for Disease Control and Prevention (CDC) is still strongly urging people to get vaccinated against the flu.
Flu vaccine is created months before each flu season, which usually starts in fall and lasts until spring. Each year, the vaccine is built from several components to combat the strains of flu that are predicted to be most common in the coming given flu season. Some brands of flu vaccine combat three strains of flu while others are effective against four strains.
Each year's flu vaccines always includes a version of H3N2 virus, since that is a common and severe strain. Production starts early because it takes time to make vaccine. This year, after one version of H3N2 was chosen and vaccine production started, a different version was found to be spreading. This strain has been seen in about half of the samples of flu virus tested this year. However, the other half of virus samples are a match the one used in this year's vaccine.
Even though it looks like the different H3N2 flu strain is more common now, this may change as the flu season progresses. Flu seasons can involve a second wave of illness caused by a different strain of the virus.
Last year's flu vaccine was about 55% effective, which is considered relatively good.
Flu, more formally called influenza, is considered one of the leading infectious causes of death in the United States. In most years, about 24,000 people die of the flu each flu season, according to the CDC.
