The influenza vaccine is only about 36% effective this year, preventing infections in just over a third of people who receive it, according to the Feb. 16 issue of Morbidity and Mortality Weekly Report.

The elderly are not among them. Although the vaccine was somewhat protective in children and adults up to 49 years old, “no statistically significant protection was observed in other age groups,” including people 65 years and older, reported investigators led by Brendan Flannery, PhD, of the Centers for Disease Control and Prevention influenza division.

That’s a concern because influenza is a killer in older people more than any other group; it sets them up for a fatal pneumonia that was once considered “the old man’s friend” because it looked like a painless way to die. The elderly are pushed more than any other group to get the shot, but it isn’t helping them this season. According to Alicia P. Budd, MPH, and her colleagues at the CDC, from Oct. 1, 2017, to Jan. 20, 2018, the weekly percentage of deaths attributed to pneumonia and influenza-related deaths has ranged from 5.8% to 10.1% and has exceeded the epidemic threshold for 5 consecutive weeks.

They also reported that the cumulative hospitalization rate attributed to laboratory-confirmed influenza for the week ending Feb. 3, 2018 (59.9/100,000), exceeded the rate for the same week in 2014-2015 (50.9/100,000), an A(H3N2) virus–predominant season, and is the highest rate observed for this week since the system expanded to include adults during the 2005-2006 season.

This year’s overall effectiveness rating was in contrast to the 2016-2017 seasonal effectiveness of 48% ( MMWR. 2017 Feb 17;66[6];167-71 ).

The CDC noted that influenza is going to be active for several more weeks, so “vaccination is still recommended,” but “treatment with influenza antiviral medications, where appropriate, is especially important this season.” Meanwhile, “influenza vaccines with improved effectiveness are needed,” the CDC said.

The estimates are based on 4,562 patients 6 months to over 65 years old presenting with acute respiratory illness in 2018 from Nov. 2 to Feb. 3 at five outpatient medical clinics scattered across the United States. Nasal and oropharyngeal swabs were tested with reverse transcription polymerase chain reaction for the presence of influenza viruses; 413 subjects were 65 years or older.

The current vaccine proved 25% effective overall for the most common cause of the flu this year, the A(H3N2) virus.

Vaccine effectiveness against the less common virus A(H1N1)pdm09 was 67%, and 42% against the even rarer influenza B viruses. Estimates were adjusted for a range of confounders, including study site, age, general health, and week of illness. Vaccination rates ranged from 45% to 59% across the study sites; 38% of the subjects tested positive for influenza, most for type A viruses. The shot didn’t work too well: 43% of the influenza cases had gotten it.

The 25% effectiveness against A(H3N2) is a bit higher than recent reports of 17% from Canada and 10% from Australia, but similar to the 32% efficacy reported in the United States for the 2016-2017 season.

“These interim estimates reflect ongoing challenges with the A(H3N2) vaccine component since the 2011-12 season,” the investigators wrote. “Multiple factors might be contributing to the reported [vaccine effectiveness] against A(H3N2) viruses this season. … Genetic changes in the vaccine virus hemagglutinin protein that arise during passage in eggs might result in a vaccine immune response that is less effective against circulating viruses.”

The investigators had no conflicts of interest.

SOURCE: Flannery B. et al. MMWR. 2018 Feb 16;67(6):180-5 ; Budd A. et al. MMWR. 2018 Feb 16;67(6):169-79.