Mumps on ice

The mumps vaccine was licensed in the US in 1967 and recommendations regarding use of the vaccine have varied since its introduction. As described in the CDC Manual for the Surveillance of Vaccine-Preventable Diseases, the Advisory Committee on Immunization Practices (ACIP)

made an official recommendation for one dose of mumps vaccine for all children at any age after 12 months in 1977. In 1989, children began receiving two doses of mumps vaccine because of the implementation of a two-dose measles vaccination policy using the combined measles, mumps, and rubella vaccine (MMR) vaccine. In 2006, a two-dose mumps vaccine policy was recommended for school-aged children, students at post high school educational institutions, healthcare personnel, and international travelers.

Mumps vaccine has had a profound impact on the annual incidence of mumps in the US. In 1968 more than 152,000 cases reported, while in 2003 only 231 cases were reported. Recently, however, the nation has witnessed a resurgence of the disease, and an apparently ongoing outbreak of mumps in the National Hockey League (NHL) illustrates how the mumps virus continues to circulate in the general population. The NHL outbreak has, so far, affected 15 players on five teams, and another three cases are suspected. A timeline of events surrounding the cases suggests the outbreak originated in October.

Doni Bloomfield wrote an article this week (which also contains "mumps on ice" in the title) that, in one vivid passage, illustrates potential infection pathways for mumps virus in professional hockey. Bloomfield quotes James Conway of the University of Wisconsin School of Medicine and Public Health:

You watch these guys taking a big hit up against the boards, there’s snot and boogers and all sorts of stuff flying around as the guy gets hit hard enough, so I don’t think it would surprise me at all that there’s some transmission just by stuff flying around during the games. It’s a sloppy, messy sport.

That's colorful imagery for sure, but in addition to how, it's important to ask why this and other recent outbreaks are occurring. Mumps is, after all, a vaccine preventable disease. 

It's possible that this group of players belongs to a demographic that has lower vaccine coverage, potentially due to parental reticence to vaccinate. However, at least one player is known to have had two doses of vaccine: one childhood dose, consistent with ACIP guidelines in the late 1980s, and another in preparation for foreign travel in February of 2014. Tara Haelle wrote an article recently on the mumps vaccine in which she quotes Paul Offit discussing the rate of waning immunity associated with this vaccine. Offit notes that

If you look at the three [MMR component] vaccines, measles and rubella induce larger memory in B and T cells . . . They have longer lasting immunity. Mumps is the weak sister of the three. You start to see vulnerability 10 years after the first dose and 10 years after the second dose.

Waning vaccine-associated immunity could thus play a role in this outbreak, and in potential future ones as well. Boosters have been used to compensate for waning immunity in past mumps outbreaks. Might a third dose of vaccine be appropriate for the general population at some point in the future?

(image source: CDC)

Influenza vaccine recommendations: Stop needling me!

Seasonal influenza is responsible for an estimated 200,000 hospitalizations and 23,000 deaths in the US annually. Each year influenza vaccines are produced based on the viruses forecast to become prevalent. There are two types of vaccine: inactivated influenza vaccine (IIV), delivered via injection, and live attenuated influenza vaccine (LAIV), delivered via a mist sprayed into the nose. Influenza vaccines typically have efficacies exceeding 60% and an estimated 46% of the American public relieves vaccine annually.

While many people are vaccinated each year, it is desirable to increase vaccination rates for at least two reasons. First, vaccine-associated immunity protects individuals from developing potentially serious or fatal disease. Second, high population coverage produces a herd immunity effect: those possessing vaccine-associated immunity cannot become infected and thus cannot infect others. This is especially important for protecting individuals for whom vaccines are contraindicated.

Individuals who are immunocompromised or immunosuppressed are such a group. Consider, for example, patients recovering from hematopoietic stem cell transplantation (HSCT) following myeloablative conditioning. In cases of imperfect donor-recipient match, patients may take immunosuppressive medications as prophylaxis against, or treatment for, graft versus host disease. During this process of immunologic tolerization, which can last months or longer, patients must avoid crowds and limit work/school and social interactions in order to avoid potentially fatal infections. And during this period it is critically important for caregivers and contacts to be vaccinated against influenza and other vaccine-preventable diseases so that they do not become infectious.

LAIV is contraindicated for caregivers of such persons in the Advisory Committee on Immunization Practices (ACIP) guidelines. Because LAIV contains live influenza viruses, a potential exists for transmission of vaccine strain viruses from vaccinees to other persons. The period of viral shedding in vaccinees is variable and relatively short lived. Vaccinated immunocompetent children, for example, shed vaccine viruses for less than 3 weeks, and evidence suggests that shedding may be much shorter lived than that. LAIV-associated shedding occurs in lower titers than is typically observed in disease-associated shedding caused by wild-type influenza viruses.

As several studies have demonstrated higher efficacy of LAIV relative to IIV in children (but see the footnote below), the ACIP has expressed

a preference for the use, when immediately available, of live attenuated influenza vaccine (LAIV) for healthy children aged 2 through 8 years, to be implemented as feasible for the 2014–15 season but not later than the 2015–16 season.

Higher protective efficacy of LAIV in children provides strong rationale for the ACIP statement. Moreover, promoting LAIV as an alternative to IIV in older patient populations may result in increased coverage in those who avoid vaccination due to fear of needles. I wonder if increased use of LAIV might pose additional risk to immunocompromised persons, however, in terms of inadvertent exposure to recent vaccinees shedding live, though attenuated, influenza viruses. Such patients may need to become more meticulous in screening visitors and contacts who may have received LAIV recently.

Footnote: During 2013-2014 there was no measurable effectiveness for LAIV against influenza A (H1N1) among children enrolled in effectiveness studies. The reasons for this are unclear.

(image source: Wikipedia)