After last year’s poor flu vaccine efficacy, public health officials think they have a much better match for the 2015-2016 season and are urging healthcare workers to be immunized to protect themselves and patients.

To drive home that point, a physician recently told a personal anecdote about possible healthcare-worker-to-patient flu transmission at a seasonal flu vaccine forum held by the National Foundation for Infectious Diseases (NFID) in Washington, DC.

“I was asked to see an older patient, who had been in the chronic care portion of our facility for about six months,” said Kathleen Neuzil, MD, professor of medicine and director of the Center for Vaccine Development at the University of Maryland School of Medicine. “We diagnosed him with a pretty severe influenza pneumonia. Then we started to ask the question: How did he get the flu? He’s not out there going to the store. The only way he could have gotten influenza is because somebody brought it to him. That could have been a healthcare worker. It could have been a family member or a friend visiting him. And so, for young and middle-aged healthy adults, protecting others should be as compelling a reason to get the influenza vaccine as protecting yourselves.”

During the 2014-15 flu season an H3N2 variant strain emerged that eluded the H3N2 coverage in the vaccine, resulting in a severe flu season.

“The 2014/2015 season had the highest hospitalization rate among seniors that we’ve ever documented,” said Tom Frieden, MD, director of the Centers for Disease Control and Prevention. “There were also 145 documented deaths from influenza among children last year. We know that the actual number is much higher, because not all flu deaths are diagnosed and detected as having flu.”

Prevailing flu strains globally are tracked before the seasonal flu vaccine is made, but influenza is notorious for mutating.

“Unfortunately, last year it changed when the flu vaccine was already being made,” Frieden said at the NFID forum. “So at that point, there was nothing really that could have been done practically. Along with manufacturers and other entities, we’re cutting down the time it takes to make a flu vaccine so that we can start making it later in the season. … Influenza is always changing. So far, what we’ve seen in the Southern Hemisphere and over the summer in the U.S. suggests that this year’s vaccine should be a good match against this year’s circulating influenza. But only time will tell for sure.”

With a stock of 171 million doses, there should be ample vaccine available.

“Overall, the flu vaccine is usually about 50% to 60% effective,” he said. “So it’s not nearly as effective as most of our other major vaccines, but it’s far more effective than anything else you can do to prevent the flu. Last year, the vaccine effectiveness of flu vaccine overall was quite low, and for H3N2 strains was very low; only about 13%,” Frieden said. “I will say that for healthcare workers, it’s particularly important to get vaccinated yourself. … We’re also concerned by the proportion of people vaccinated among those who work in long-term care facilities, such as nursing homes. Prior studies have suggested that if the people who work in nursing homes don’t get a flu vaccine, the [residents] are much more likely to get the flu and become severely ill.”

Of course nursing home residents should be immunized as well unless medically contraindicated. This recommendation may have saved a few lives last year when residents immunized with the subpar flu vaccine still managed to survive an outbreak of H3N2 influenza A at a nursing home in Canada.

“Even with the challenge of the 2014/15 vaccine drift, the likelihood of contracting influenza was lower in immunized compared to unimmunized residents, although the difference was not statistically significant,” investigators reported.1 “Lack of detection of a significant effect may be explained, however, by low power given the small sample size.”

Overall, 32 of 45 nursing home residents had received the influenza vaccine more than two weeks prior to the outbreak. Twenty-two of the 45 residents developed influenza-like illness. The attack rate was higher in the unimmunized residents (62%) compared to the immunized residents (44%). Similarly, the hospitalization rate was higher in the unimmunized (25%) than in the immunized (7%).

The drifted H3N2 virus is included in the 2015-16 vaccine, which was based on an analysis of the primary viruses circulating in the Southern Hemisphere and the U.S.

“There were 199 analyzed specimens,” Frieden said. “Of those, most [118] were the H3N2 type that is closely related to this year’s vaccine strain. Another 20 were the H1N1 that’s still circulating from back in 2009 — also, very closely related to what’s in the vaccine strain. And then there were 61 influenza B strains that were evenly matched between two different strains that are included in the quadrivalent vaccine. Also, all of the strains analyzed were susceptible to the antivirals — oseltamivir, zanamivir and peramivir.”

REFERENCE

  1. Eruvwetaghware E and Winquist B. 2014 flu shot, vaccine drift: A retrospective cohort study of an outbreak of influenza A (H3N2) in a nursing home. IPAC Canada 2015 National Education Conference. Victoria BC: Jun 14-17, 2015.