The flu vaccine has flopped again due to a virus that prevailed after the season had begun.
National health experts reported Thursday an overall influenza vaccine effectiveness rate of 29%, a drop from a 47% effectiveness rate in February.
There was no “significant protection” against illnesses that emerged from a new viral strain, according to a presentation by the Centers for Disease Control and Prevention.
Last season, the flu was caused by the H1N1 and H3N2 viruses in roughly equal proportion, the CDC told The Washington Times. While the vaccine reduced the risk posed by the H1N1 viruses, it did not protect against H3N2 viruses that rose to prominence, the agency said.
This year saw the lowest effectiveness rate since the 2014-2015 season, when the vaccine was 19% effective. The CDC said it saw a “drifted H3N2 strain” that season as well.
Barbara Loe Fisher, president of the National Vaccine Information Center, said health experts have had problems with influenza vaccines for years, with effective rates usually below 50%.
“Every year, they basically have to guess which influenza strains are going to be most prevalent,” said Ms. Fisher. “Because the influenza virus, it changes rapidly.”
“Historically, they’ve had a problem ever since the influenza vaccine was first used decades ago. They’ve had a problem with getting it right, and this is a recurrent problem,” she said. “I think that part of the issue is that there are some gaps in the science.”
The influenza has caused between 9.3 million and 49 million illnesses, between 140,000 and 960,000 hospitalizations, and between 12,000 and 79,000 deaths in the United States each year since 2010, the CDC estimates.
For this flu season, there were between 37 million to 42.9 million illnesses, 531,000 to 647,000 hospitalizations and 36,400 to 61,200 deaths in the U.S.
Ms. Fisher said people have the wrong idea that they won’t get the flu if they got the shot.
“It’s important for people to understand when they get a flu shot, they need to understand that shot may not protect them,” she said.
But the CDC said the flu vaccine can alleviate the severity of illnesses in people who are vaccinated but still get sick. The health agency added that vaccinations can reduce hospitalizations, ward off serious medical events associated with some chronic conditions, protect pregnant people before and after birth, save lives and prevent others from contracting the flu.
The CDC recommends everyone 6 months or get a flu shot each year.
The World Health Organization already has made a selection for the H1N1 virus for the 2019-2020 flu vaccine, but it is delaying a decision on the H3N2 vaccine. The CDC has recommended the components that vaccines should included for the next flu season.
Ms. Fisher said looking at the flu season in Australia and New Zealand can help predict how serious the flu season in the U.S. will be and the effectiveness of the vaccine.
Vaccine effectiveness rates average around 40%. The highest flu vaccine effectiveness rate was 60% from 2010-2011 while the lowest was 10% from 2004-2005, the CDC reports.