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Published on 2 Comments on Is There a Problem with This Year’s Flu Vaccine?

I know I'm in trouble when I first hear about an infectious disease problem through the lay press. In the case of this year's flu vaccine, it was NPR, about a week ago. It looks like it started turning up on some national news feeds a few days earlier, and the message was that estimates of vaccine efficacy from Australia (the southern hemisphere flu season is winding down) were around 10%.

As is my usual practice, I go to the source data, which in this instance wasn't easy since virtually none of the lay press announcements included a link to that source. I finally traced it back to an online publication from October 26, 2017, and I'm still wondering why it didn't make more a splash back then, rather than 6 weeks later.

Based on interim reports of flu activity in Australia through late September, investigators did determine vaccine efficacy to be 10% (95% confidence interval -16 to 31) for influenza A H3 strains for all age groups; A H3 are the most common strains circulating this season. They used a test-negative study design for flu-positive patients seeking medical attention in sentinel clinics, which is a standard approach for flu vaccine efficacy research. Overall vaccine efficacy against all subtypes of influenza A and B was a more respectable 33% (17 to 46). Efficacy against A H3 strains varied by age. Children under 15 years of age and adults 15-64 years experienced rates of about 15% efficacy, while adults 65 and older having essentially no efficacy for A H3 strains. These numbers, if true, are not unprecedented with A H3 strains and have resulted in heavier flu seasons in the past.

It's too early to tell whether these estimates will hold for Australia once all data are available, and of course it's still too early to make an estimate for the US. A season with lower vaccine efficacy can mean greater risk of serious outcomes in high-risk populations, and this risk will be even greater if news about the lower efficacy results in fewer people seeking immunization this year. For now, it's important to stress that everyone should be immunized for influenza.

You can keep track of influenza season at the CDC and the Maryland Department of Health websites.

Published on Leave a comment on Why Do We Vaccinate Against Mumps?

At the Montgomery County Pediatric Society meeting on December 4, 2017, Dr. Stuart Taylor asked me a very thought-provoking question. During a discussion of the numerous mumps outbreaks on college campuses and elsewhere recently, he wondered whether the effort and expense of tracking cases and immunizing in special situations was worthwhile, considering that mumps is a relatively mild illness. He recalled being told some decades ago that the mumps vaccine was included with the measles and rubella vaccines, both of which protect against infections with very serious complications, more out of convenience than for a compelling public health benefit. That question sent me back to the medical literature, and I learned (or maybe re-learned) some interesting points. Bottom line: mumps isn't as mild as most pediatricians think.

I wanted to first find recent information on mumps in more industrialized countries, but that isn't as easy as it sounds. However, studies on mumps outbreaks primarily in adolescents in England in 2004-5 offer some sobering statistics. In the United Kingdom, MMR vaccine was introduced in 1988 as a single dose for children 12-15 months of age, followed by a recommendation in 1996 to add a second dose to the routine immunization schedule. The 2004-5 epidemic largely affected individuals who were born too early to be offered the initial vaccine, but also protected somewhat during their childhood by a high vaccination rate in younger children, such that they weren't as likely to be exposed to the wild virus. Yung et al mined various databases in England and Wales from 2002-2006 and estimated that mumps infection resulted in 2647 case-patients being hospitalized, or about 6% of all mumps cases. That alone certainly would justify universal mumps immunization programs. These investigators also estimated hospitalization rates for some of the mumps complications: 4.4% for orchitis, 0.35% for meningitis (note aseptic meningitis is very common in mumps, about 50%, but is very mild usually), and 0.33% for mumps pancreatitis.

Mumps also is a cause of hearing loss, sometimes severe. A recent Japanese study was able to locate and confirm 67 cases of mumps hearing loss. Only 15 of them had obvious clinical mumps infection by history, and over 90% of these cases had severe hearing loss, though this latter figure may be inflated due to ascertainment bias. It is important to note that Japan is an outlier among developed countries in how they immunize for measles, mumps, and rubella.

A few interesting references:
Hviid A, et al. Mumps. Lancet 2008; 371:932-44.
IASR. Mumps (infectious parotitis) in Japan, as of September 2016. IASR 2016; 37:185-6. Online at https://www.niid.go.jp/niid/en/index-e/865-iasr/6843-440te.html.
Morita S, et al. The clinical features and prognosis of mumps-associated hearing loss: a retrospective, multi-institutional investigation in Japan. Acta Oto-laryngol 2017; 137 (Suppl 565):S44-7.
Yung C, Ramsay M. Estimating true hospital morbidity of complications associated with mumps outbreak, England, 2004/5. Euro Surveill 2016; 21, online at https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4998425/.
Yung C-F, et al. Mumps complications and effects of mumps vaccination, England and Wales, 2002-2006. Emerg Infect Dis 2011; 17:661-7.

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