How effective the vaccine is in preventing the flu depends on how good a match it is to the strains of flu virus circulating that year. Most years, the vaccine is between 40 percent and 60 percent effective, according to the CDC.
Last year, the vaccine offered little protection against the most common flu strain that circulated, an H3N2 virus, Jhung said.
That happened because the virus that experts predicted to be the predominant strain wasn’t, and the new H3N2 virus was not included in the vaccine, he explained.
This mismatch caused a severe flu season, especially for the very old and very young, and led to a record number of hospitalizations for flu among the elderly, according to the CDC.
This year’s vaccine contains the new H3N2 strain, but it’s too early to tell which strains will dominate, Jhung said. “If things continue as they are right now, we will see a season where the vaccine is a good match for the circulating flu viruses,” he said.
This year’s vaccine also includes two other strains that are expected to be around as well, according to CDC officials.
“Tons of vaccines are available,” Jhung said. Manufacturers are expected to produce 170 million to 180 million doses.
Dr. Marc Siegel, an associate professor of medicine at NYU Langone Medical Center in New York City, said “everyone needs to get a flu shot, because it creates a ring of immunity inside your household and protects your pregnant wife or your young child or your elderly parent.”
The more people who are vaccinated, there is less circulating virus and fewer people are at risk, he said.