We all need a little good news from time to time. Vaccines have been a remarkably successful medical invention. Over the past year, just 12 cases of polio have been seen worldwide. Truly amazing. Also reported is that measles has fallen below 100,000 cases worldwide for the first time. A few weeks ago New Zealand was formally named as free from measles arising from within the country.
In 1998 there were 350,000 cases of polio from over 125 countries. For some patients the paralysis spreads to the muscles helping them to breathe, killing them (about 2-10% of cases). Polio most often affects kids younger than five years old, but there is post-polio syndrome where people can experience symptoms 15-40 years later.
Getting polio down to a dozen cases in just two countries looks damn good, but to prevent it from coming back we’ve got to eliminate it entirely. As long as there is a reservoir of the disease, it can come back at us.
If humans are the primary host of a vaccine-preventable disease, it can be eliminated with comprehensive worldwide vaccination.
As the WHO polio fact sheet says, “there is no cure for polio, only prevention.” To get rid of polio we have to prevent it out of existence.
Eradicating diseases are huge, long-haul efforts involving a wide range of expertise and on-the-ground work.
War-torn, very poor or remote areas are hard to vaccinate, and tend to be the last hold-outs of these diseases. For polio, the last two countries are Afghanistan and Pakistan. The Gates Foundation is putting $US450 million into the final stage: it’s a big effort to make sure the end-game sticks. Among other things, closing off polio involves a switch to a different vaccine.
There are three main types of polio. Type 2 has already been eliminated worldwide, and no wild type 3 polio virus case has been seen since 2012. Vaccination is being shifted to a vaccine for just the remaining two types of polio, types 1 and 3. A rare side effect is circulating vaccine-derived polioviruses (cVDPV), which is mostly (90% of the time) caused by type 2 poliovirus. Removing type 2 polio from the vaccine should reduce how often cVDPV occurs. There’s also a backup stockpile of a vaccine for just type 2 polio, just in case.
The Global Polio Eradication Initiative has an interactive map, comparing where polio was over a time frame.
The full situation is slightly more complicated.
In three countries—Afghanistan, Nigeria and Pakistan—polio is endemic, having never been eradicated. The two countries that have cases over the past year are Afghanistan and it’s neighbour Pakistan.
The Democratic Republic of the Congo and Syrian Arab Republic have stopped poliovirus cases from within their country, but are experiencing re-infection from other countries. In some (most) cases this is from vaccine-derived poliovirus.
On top of this there are also 17 key at-risk countries, countries with low levels of immunity and/or low levels of disease surveillance. (I’m writing this in one of them, the Lao People’s Democratic Republic.)
While the end of “wild” polio looks to be in sight, in the case of measles the end is some way off but it’s great to learn worldwide cases have fallen to fewer than 100,000 per year. Measles is often considered one of the most contagious diseases and can have serious consequences, but we can eliminate it. Measles is particularly common in parts of Africa and Asia. Other countries, like New Zealand, still have measles cases, but they don’t arise from within the country – instead they occur when people bring measles with them from overseas. Most of the people who subsequently get measles in these countries are those who have not completed a full measles vaccination schedule. For example in New Zealand, the Ministry of Health’s Acting Director of Public Health, Dr Stewart Jessamine, said about last year’s outbreak,
89 people contracted measles during the outbreak. Of those, 71 had not been vaccinated against the disease, nine had been vaccinated within two weeks of measles symptoms appearing and three were only partially vaccinated.
Earlier this month it was announced that New Zealand hasn’t seen any new cases from within New Zealand for three year. We’re free of measles from New Zealand. Yay! But to stop it spreading within New Zealand when someone brings it in from overseas, we need to keep vaccination levels high.
According to the NZ Ministry of Health, “Anyone born from 1 January 1969 who has not had two doses of the vaccine is eligible for free vaccination from their family doctor.”
The Unforgiving Math That Stops Epidemics, by professor of epidemiology and infectious-disease researcher Tara Smith is an excellent article looking at how maths can help tackle the spread of diseases. It’s promoted by no less than Chelsea Clinton, too! (Chelsea Clinton has a Masters in Public Health.) Measles has a particularly high rate of transmission to others,
For measles, with an R0 of 12 to 18, you need somewhere between 92 percent (1 – 1/12) and 95 percent (1 – 1/18) of the population to have effective immunity to keep the virus from spreading. For flu, it’s much lower — only around 50 percent. And yet we rarely attain even that level of immunity with vaccination.
One catch for the measles elimination effort is that coverage is stalled at about 85%, rather than the 92-95% coverage needed. Measles vaccination needs two shots for full protection. The second vaccine has only been taken up in 64% of people, a long way short of what is needed. Because measles is incredibly infectious—it’s considered the most contagious illnesses—large outbreaks can occur where there is poor vaccination.
Another catch with eliminating measles worldwide is that a lot of the work is done in conjunction with eliminating polio by giving out vaccines for measles and other illnesses such as rubella at the same time. Once the polio elimination effort is completed potentially there could be a rebound of measles in countries with poor measles coverage.
Rubella is part of the Measles and Rubella Initiative, a partnership of the American Red Cross, the US Centers for Disease Control and Prevention, the United Nations Foundation, UNICEF, and WHO formed in 2001. I won’t cover rubella here, but you can read a little about it in an earlier piece I’ve written, Rubella, not a benign disease if experienced during early pregnancy.
The feature image for this post shows Jonas Salk, a key figure in the development of the polio vaccine. Yesterday was his birthday. He’d have been impressed how far this has come, and the huge effort that has been put in.
Tackling diseases involves all kinds of expertise and contributions. Epidemiologists tracking outbreaks and modelling what happens if it’s tackled different ways. Logistics support. On-the-ground community efforts. Funding agencies and donors. Vaccine development and production teams. And many more. There’s also some very geeky laboratory and computational stuff that maybe I can present a little of some other time. In the meantime, let’s raise a cheer for all these people bringing on a world with less disease.
Other articles on Code for life
I’ve put up this while I work on glyphosate, genetic modification, gene therapy and other related things. I was going to add some recent research on influenza, but I need to get to other writing! I had wanted to get this up for the weekend, but it seems it’s too late. Time zone differences and other obstacles do that…
There’s poliovirus infection and there’s polio. If poliovirus infection causes paralysis we know as polio.
It perhaps gives some illustration of the importance of addressing low vitamin A levels in developing nations in that WHO estimate about 1.5 million lives have been saved through systematically giving out vitamin A along with the polio vaccine. This is relevant to me another way. I also write on genetic modification (GM). A number of GM efforts are aimed at increasing vitamin A levels in food to address deficiency in poorer nations. It’s a continuing frustration to some of us that some people who you could describe as ‘the worried Western wealthy’ oppose GM food, which it could do so much good.
There are other eradication efforts going on. Two diseases have been eradicated: smallpox and rinderpest (in cattle). Eradication is underway for polio (poliomyelitis) and guinea worm (dracunculiasis; only 13 cases reported so far this year). Some other diseases have been eradicated in particular regions. These include: hookworm, malaria, lymphatic filariasis, measles, rubella, onchocerciasis, yaws, bovine spongiform encephalopathy (BSE). (Source: Our world in data; data should be confirmed independently.)
Jonas Salk holding bottles of culture used to grow the polio vaccine. Source: Wikipedia, public domain. Yesterday (October 28th) was Jonas Salk’s birthday.