Japan is in the midst of a rubella outbreak that has already infected over 5,000 people in just the first four months of this year. Since the early 2000s, the country has undergone cyclical five-year rubella epidemics, with community-wide outbreaks cresting in the spring and summer. But in the past two years the number of infections has surged dramatically from a hundred-odd cases every year into the thousands, and a weird epidemiological pattern has emerged thanks to a quirk in Japan’s vaccination policy in the 1970s: 77% of cases in the rubella outbreak have occurred in men over the age of 20 (1).

A transmission electron micrograph (TEM) showing an assemblage of rubella virions. Image: Dr. Erskine Palmer, CDC. Since the 1970s, many of us have had the option of being vaccinated against this fever and rash-causing virus through combination inoculations such as the measles-mumps-rubella (MMR) vaccine or the measles-rubella (MR) vaccine. But in 1976, Japan began a national immunization campaign using a vaccine protective exclusively for rubella, a “single-antigen rubella vaccine,” and targeted schoolgirls enrolled in junior high. It may seem baffling to exclude an entire gender from vaccination of a disease that is decidedly not gender-neutral in its pattern of infection but this program was implemented for the purposes of preventing rubella infection in unborn children, known as congenital rubella virus infection (CRS). A fetal infection with the virus in the first 16 weeks of pregnancy may result in miscarriages, stillbirths, and birth defects such as cataracts, hearing impairments, and heart defects. By vaccinating only girls, the problem of CRS and its attendant tragedies in future Japanese generations would be effectively nullified. This tactic was used for 13 years until the introduction of the MMR and then the MR vaccines that would then take care of a gang of childhood diseases in one swift shot to the arm. Now Japanese children are well protected against the transmission of rubella - a survey of population immunity against the virus found that over 80% of those aged 1 to 18 years were protected, with infants and toddlers reaching protection levels of over 90% (1). In the ongoing 2013 outbreak, only 5.6% of the cases were children aged under 15 years.

Whoa now!: The number of rubella cases, by sex and age group in Japan from 2009–2013. In 2012, the number of rubella cases sharply increased to 2,392, with the rise in cases continuing into 2013. Image: CDC, see Reference 1. But there still exists a massive gap in vaccination coverage among the population, specifically this susceptible cohort of boys who are now grown men that missed out on the rubella vaccination party in the late ‘70s and early ‘80s. It turns out that a good number of these men have suffered from a bout of a rubella in the past two years. As the CDC noted in their June report on the outbreak,

In the current outbreak, males aged 20–39 years, many of whom had not been vaccinated in the initial rubella vaccination program for male junior high students offered only in clinics and hospitals, have accounted for 46% of reported cases (1).

An article on the outbreak in the New York Times noted that many outbreaks have occurred in the workplace, a setting ripe with men in the 20-39 age group (2).

An evident gender disparity: The number of rubella cases among Japanese males and females, by age and vaccination history, for the first seventeen weeks of 2013. As we know all too well, history relishes repeating itself ad nauseam. What will happen to the generation of boys and men who were not vaccinated against human papillomavirus (HPV) alongside their female peers in the past decade? In the United States, nearly 10,000 men are diagnosed with HPV-associated head-and-neck cancers annually (3). In two to three decades will we see the echoes of a similar “girls only” vaccination policy among men infected with HPV and suffering from HPV-associated cancers? As Maggie Koerth-Baker writes in an article for Boing Boing examining both the known and unknown unknowns of HPV-associated cancers in men,

From a biological perspective, HPV doesn't much care about what you have going on between your legs and we're doing ourselves a disservice by ignoring that reality. In fact, as we've focused on preventing cancer of the cervix (which, for obvious reasons, really only affects women) we've overlooked a growing problem that disproportionately affects men (4).

As both the rubella outbreak and the the biological realities of HPV infection underscore, it’s worth remembering that public health is not always a clearly delineated matter of age, gender, or race. For most infectious diseases the only matter of importance in its host-seeking behavior is that a human being has a pulse. Resources From the NYT, a report on the 2011 endorsement for the HPV vaccine for boys. The Case for a Gender-Neutral (Universal) Human Papillomavirus Vaccination Policy in the United States It's hard convincing people to get vaccines nowadays but maybe Star Wars could once again lend a (robot) hand to the public health world. References 1) Centers for Disease Control and Prevention (CDC). (June 14, 2013) Nationwide Rubella Epidemic — Japan, 2013.Morb Mortal Wkly Rep; 62(23): 457-62 2)DG McNeil Jr (June 24, 2013) Rubella Epidemics in Japan and Poland. The New York Times [Online]. Accessed here. 3) Division of Cancer, Centers for Disease Control and Prevention (CDC) (2012) Human papillomavirus–associated cancers—United States, 2004–2008. Morb Mortal Wkly Rep; 61(15): 258–261 4) M Koerth-Baker (July 9, 2013) HPV cancers a mystery in men. Boing Boing [Online]. Accessed here.

Centers for Disease Control and Prevention (CDC) (2013). Nationwide rubella epidemic - Japan, 2013. MMWR. Morbidity and mortality weekly report, 62 (23), 457-62 PMID: 23760185