Flu vaccines are based largely on information that lags.
The panel bases its decisions on data about the common strains circulating around the globe throughout the year. In some years, the vaccine is a better match to strains that hit the US than others. Even in a good year, the effectiveness of the vaccine is about 60%. Other times, it can be as low as 10%.
This season, based on data from 3,636 kids and adults who got the flu between October and mid-February, the vaccine did not seem to reduce their risk of getting sick from the influenza A (H3N2) viruses that have been predominant. The overall vaccine effectiveness against infection was 16%, which is considered not statistically significant. However, there was not enough enrollment in the study for a reliable understanding of how effective it was.
The details were published Thursday in the CDC’s Morbidity and Mortality Weekly Report.
“I can not remember an ineffectiveness that was much lower than that,” said Dr. William Schaffner, a professor in the Division of Infectious Disease at Vanderbilt University Medical Center, who did not work on the report. “It was definitely off-target this year.”
The CDC is studying how well the current vaccine protects against severe illness. That’s largely why the agency still recommends that people get the vaccine. Even if it may not keep you from being infected, “vaccination can prevent serious influenza-related complications caused by viruses that might circulate later in the season, including 2009 pandemic A (H1N1) and influenza B viruses,” the study said.
CDC spokesperson Kristen Nordlund also told CNN in an email that the agency recommends the shot “even when protection against one virus is reduced since flu vaccines protect against four different viruses.”
Final data about the effectiveness of this vaccine will be released later this year. Nordlund said people should look at the current information with bail.
“Assessing [vaccine effectiveness[ when there has been little flu circulating and in the midst of the Covid-19 pandemic is complicated and the estimates are not as rigorous as when there is more flu circulation,” Nordlund said.
“As we say in this business: If you’ve seen one flu season, you’ve seen one flu season,” he said.
“We need to continue funding the research to create a better influenza vaccine,” Schaffner said. “Going forward, flu is going to continue to appear around the world and make annual epidemics that cause incredible amounts of illness, social and economic disruption, so we clearly need a better influenza vaccine.”