CDC: Flu vaccine matches early strains; 40 million doses distributed

Issue: October 2015

At least 40 million doses of the influenza vaccine have been distributed this season, and early diseases indicate that the vaccine formula is in close correspondence with circulating viruses, according to the CDC.

During a press conference, CDC Director Thomas R. Frieden, MD, MPH, said there will be more influenza vaccines produced by manufacturers than ever before — at least 171 million doses.

Thomas R. Frieden

The vaccines have been updated to better match the predominant H3N2 strain that circulated last season. As previously reported, the formula composition for 2015-2016 trivalent vaccine includes hemagglutinin (HA) derived from an A/California/7/2009 (H1N1)-like virus, an A/Switzerland/9715293/2013 (H3N2)-like virus, and a B/Phuket/3073/2013-like (Yamagata lineage) virus. These vaccines will be included in quadrivalent influenza vaccines, along with a B/Brisbane/60/2008-like (Victoria lineage) virus.

“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,” Frieden said. “But only time will tell for sure. Even in a year when the [influenza] virus isn’t well matched, [vaccination] remains the single-best thing you can do to protect yourself, your family, and your community against influenza.”

According to a recent MMWR, 118 out of 199 influenza specimens collected between May 24 and Sept. 5 contained the H3N2 type. The remaining specimens included 20 H1N1 strains and 61 influenza B viruses.

The efficacy of last season’s vaccines for H3N2 strains was 13%, which was much lower than the typical 50% to 60% range, Frieden said.

“Last season was unusual,” William Schaffner, MD, Infectious Disease News Editorial Board member from Vanderbilt University School of Medicine, said during the conference. “Not only did we have one strain of influenza that caused almost all of the reported [influenza] cases, but it was different; it had mutated.

William Schaffner

“I’m pleased to say that so far, as we track influenza viruses, this year the ones that are causing very early disease are exactly as was predicted So it looks to me as through the vaccine is going to be well [protective].”

Forty-seven percent of the U.S. population was vaccinated during the 2014-2015 season, according to the National Foundation for Infectious Diseases (NFID). The highest coverage rate was in children aged 6 to 23 months at 75% — the only age group to meet the public health vaccination coverage goal of 70%. The vaccination coverage rate was 68% in children aged 2 to 4 years; 62% in children 5 to 12 years; less than 40% in adults 18 to 49 years; and 67% in seniors 65 years and older.

Although influenza vaccination rates have increased over the past few years, Frieden said more coverage is warranted, particularly among young and middle-aged adults. He confirmed that at least 145 pediatric deaths were due to influenza last year, and there were more hospitalizations among seniors than ever recorded. Another “concerning” trend was observed in pregnant women, who had an estimated 50% coverage rate despite their increased risk for complications.

The CDC highlighted the critical role of health care providers in vaccination efforts among pregnant women. Women who had at least one visit to a health care provider since July 2014, including those with negative attitudes, were more likely to receive the influenza vaccine when it was recommended and offered to them by a health care provider (67.9%) compared with women who were only recommended the vaccine (33.5%) or were not recommended the vaccine at all (8.5%), according to another MMWR.

The NFID is urging health care professionals to lead by example and make influenza prevention a public health priority, Schaffner said. A separate MMWR showed there was increase in vaccination coverage among health care providers (77.3%). The highest coverage rate was in hospital staff at 95% and the lowest rate was in long-term care facility staff at 63.9%.

“We’re also concerned by the proportion of people vaccinated among those who work in long-term care facilities, such as nursing homes,” Frieden said. “Prior studies have suggested that if the people who work in nursing homes don’t get [an influenza] vaccine, the people who are living in the nursing home are much more likely to get [influenza] and become severely ill.”

Frieden and Schaffner also emphasized the importance of pneumococcal vaccinations, which are recommended for patients older than 65 years and patients with certain chronic health conditions, such as diabetes or lung disease. In June, the Advisory Committee on Immunization Practices voted to extend the recommended interval for adults receiving Prevnar 13, the 13-valent pneumococcal conjugate vaccine (PCV13, Pfizer); and Pneumovax 23, the 23-valent pneumococcal polysaccharide vaccine (PPSV23, Merck); from 6 months to at least 1 year apart, regardless of sequence.

Frieden concluded the conference with three “call to action” steps: get vaccinated; prevent the spread of influenza by staying home when sick; and take antiviral medications when needed.

“Let’s hope for an uneventful [influenza] season,” Schaffner said. “But as we’ve heard from these experts, our best defense is a good offense. Get vaccinated.” – by Stephanie Viguers

Disclosure: The researchers report no relevant financial disclosures.

Reference:

Black CL, et al. MMWR. 2015;64:993-999.

Blanton L, et al. MMWR. 2015;64:1011-1016.

Ding H, et al. MMWR. 2015;64:1000-1005.