The deadly flu season could be linked to low vaccination rates

De Lena H. Sun | Washington Post

In the United States, fewer than 4 in 10 adults were vaccinated against influenza last winter, the lowest rate in seven seasons and one of the reasons the 2017-2018 season was the deadliest in decades.

The reports released Thursday by the Centers for Disease Control and Prevention provide new details describing the severity of the influenza season in which more people have been killed than any other seasonal flu since the 1970s.

Vaccination against influenza is the main way to prevent illness and death caused by influenza. But last season, adult vaccination coverage was 37.1%, a decrease of 6.2 percentage points from the previous season. This is the lowest rate for adults aged 18 and over since 2010-2011.

"It's huge – it's a striking inflection from the previous year," said William Schaffner, infectious disease specialist at Vanderbilt University and medical director of the National Foundation for Infectious Diseases.

Data released on Thursday also provides a complete picture of the impact of last year's fatal respiratory virus. Some data on deaths and hospitalizations were released last month, but new details show how tough last season was. The CDC believes that:

-49 million people were affected by the flu, about the total population of Texas and Florida.

– 960,000 people were hospitalized, more than the total number of hospital beds staffed in the United States.

79,000 people died, the average number of people attending the Super Bowl. According to analyzes conducted more than three decades ago, the previous peak for a normal influenza season was 56,000 deaths.

Last winter's flu season was so devastating for a number of reasons. He was dominated by a particularly fierce viral strain. According to the experts, the seasons when H3N2 is dominant generally result in the greatest number of complications, especially for the very young and the oldest. Vaccines are also less effective against H3N2. The virus is changing rapidly, requiring new seasonal vaccine updates and making the immune system much more difficult to generate a good response.

The drop in immunization coverage could also have contributed to the severity of last season, said Alicia Fry, head of epidemiology and prevention in the CDC's influenza division. Although far from perfect, the influenza vaccine reduces the number of serious illnesses and complications such as hospitalization and admission to intensive care units.

Schaffner and CDC officials said the decline in immunization coverage may be linked to preliminary reports of low vaccine effectiveness in Australia. Influenza activity in the southern hemisphere can often predict the expectations of Americans.

"I think it really discouraged a lot of people from getting vaccinated," said Schaffner, who also noted that the initial data was incorrect.

It is too early to know if people "always keep this in mind," he said.

It is too early to predict what will be the next flu season. Influenza activity is low, but a child death has already been reported. Last season, the flu killed 183 children, the highest number since the federal health authorities started tracking child deaths 14 years ago.

This year, CDC officials hope to improve immunization coverage by helping doctors and nurses convince their patients to get the flu shot. A strong recommendation from a clinician makes all the difference in whether a person is vaccinated against the flu.

Cindy Weinbaum, Deputy Director of CDC's Division of Immunization Services, may have thought that last season would not have been worthwhile to get vaccinated.