We’re spending National Infant Immunization Week in Baltimore at the National Foundation for Infectious Diseases Annual Conference on Vaccine Research. It’s three full days of sessions focused on research into existing and new vaccines, as well as research on epidemiologic and public health aspects of infectious diseases and vaccines. One of the main threads at the first day of the conference was disease eradication.
DA Henderson, MD, opened the conference with a keynote address on the feat of smallpox eradication through vaccination. He highlighted the unique qualities of smallpox that made it an ideal candidate for eradication and compared some of these factors with parallel characteristics of polio. (Dr. Henderson discussed some of these characteristics of smallpox in our interview with him.) In every category, polio is a more complicated disease
Henderson suggested that the campaign against polio needs what was so important in eradicating smallpox: a more antigenic and heat stable vaccine. And though the WHO ultimately was able to defeat smallpox, Henderson reminded the audience that it was a tremendously difficult task given the unstable political situations in endemic countries – especially Bangladesh – in the 1970s. The complicated situation in Pakistan now may present challenges to polio eradication that can’t be overcome.
Walter Orenstein, MD, followed Henderson’s talk with a look at the potential for measles and rubella eradication. He noted that it seemed fair to start by asking whether measles and rubella can be eradicated, whether they should be eradicated, and whether they will be eradicated. The last question is, of course, the most complicated
Strebel and Moss (2011) introduced a set of criteria to determine whether a disease is potentially eradicable, and Orenstein expanded on them:
- Is there an effective, practical intervention for the disease?
- Are there practical diagnostic tools?
- Are humans essential for the pathogen’s life cycle, or are there other hosts?
- Has there been success in eliminated the disease from a large geographic area?
For all questions, the answers point to the possibility of eradicating measles and rubella.
- Both measles vaccine and rubella vaccine are highly effective at preventing disease and preventing transmission (measles especially so after two doses).
- For both diseases, we have reliable antibody assays for diagnostic use.
- There is no other primary animal host for either pathogen (although some nonhuman primates can be infected with measles, humans are essential for continuous transmission). Moreover, there is no chronic carrier stage with measles or rubella as there is with a pathogen such as hepatitis B).
- The Americas have successfully eliminated measles and rubella (occasional importations aside).
Therefore, says Orenstein, both measles and rubella meet the biologic criteria for eradication. And in terms of global morbidity and mortality, they certainly deserve the attention that eradication campaigns would bring. In 2011, there were still about 158,000 deaths from measles – down a great deal in 10 years, but still a significant burden. Estimates have put the cost for eradicating measles by 2020 at a discounted $7.8 billion, which would avert a discounted 346 million disability-adjusted life years between 2010 and 2050, which is fairly good cost effectiveness.
WHO’s recommended strategy for addressing measles and rubella is routine two-dose immunization with measles and rubella-containing vaccines via routine immunization, supplemented by mass campaigns where vaccine uptake is low. (Not all countries use rubella-containing vaccine yet, but the WHO recommendation is that they add it once their measles vaccine coverage is about 80%.)
Challenges to measles eradication by WHO region include
- The Americas face the risk of importations from abroad, plus pockets of low vaccine coverage in certain communities
- Africa’s challenges include a weak immunization and health infrastructure, as well as security concerns limiting access to undervaccinated pockets
- Europe faces vaccine hesitancy in its western areas
- The Southeast Asian region has large decentralized countries like India and Indonesia, which make routine immunization difficult, as well as the problem of vaccine hesitancy in Japan.
Orenstein concluded by saying that he hopes he demonstrated that measles and rubella can and should be eradicated. The question of whether they will be eradicated can be answered with “yes” provided that we’re willing to extend the timeframe farther into the future.
Philip Minor, PhD, from the National Institute for Biological Standards and Control in the UK addressed the complex problem of polio eradication. Much of his talk focused on the need to eradicate vaccine-type viruses once the wild viruses are eradicated. This is already the situation with Type 2 poliovirus, which has not been seen in its wild form since 1999. Type 3 poliovirus may be heading this way as well: Minor noted that no wild Type 3 virus has been detected in about five months.
WHO has recently accepted recommendations from SAGE to introduce a single dose of inactivated polio vaccine to target vaccine-derived Type 2 polio before administration of Types 1 and 3 oral polio vaccine. As the other types are eliminated in the wild, OPV will cease to be used and will be entirely replaced by IPV.
Minor closed with musings on the safety of the vaccine viruses used in producing IPV, suggesting that less virulent viruses should be used to avoid another Cutter-like incident. Indeed, he is working on modified Sabin-type vaccine viruses that are not capable of causing disease in humans.
Tomorrow we’ll post on Day 2 proceedings from the conference, many of which concerned immunization for diseases that affect pregnant women and young infants.