A study published today in the Lancet brings some exciting news on the polio vaccine front. There has been tremendous progress globally at eradicating polio since a global eradication effort was launched in 1988, but as the polio folks have learned all to well is that progress against this disease is not a linear battle (take note malaria folks). In essentially the first 20 of the eradication effort years, cases of polio were reduced by 99%, however, the last 1% has remained elusive.
Part of the problem stems with the effectiveness of current vaccine formulations. There are three strains of the polio virus that cause significant illness: type 1, type 2, and type 3. One can develop a vaccine against one or more of these strains, however, in general adding another strain means reducing the overall effectiveness of the vaccine against the included strains. Coverage is traded off with effectiveness. Until recently, we had monovalent (meaning one strain) vaccine formulations against each of these strains as well as a trivalent formulation which contained all three.
The trivalent vaccine was the workhorse of the eradication effort – it was what helped get us to where we are today, But because the trivalent vaccine is not perfectly effective there are always enough cases of the diseases to allow it to continue to spread in the population. The solution to date is to switch to the monovalent vaccine, usually for type 1, which is much more effective than the trivalent vaccine. The problem, of course, is that if only the type 1 vaccine is given, people are not protected against the other strains of the virus, leaving them vulnerable.
The type 2 strain of the virus has essentially been eliminated and is therefore no longer a priority. The inclusion of this strain in the vaccine might therefore be interfering more than it is helping. This new study investigated the effectiveness of a bivalent vaccine – against types 1 and 3 and found that it was nearly as effective as the monovalent formulation of either strain and more effective than the trivalent vaccine. In this case two is company but three is a crowd. This is good news – it is believed that this new vaccine could be adopted quickly and could be used in this next phase of the eradication effort.
Polio eradication still faces many important challenges going forward – perhaps most notably the fact that the effort is only funded at the level of about half of what is needed to carry on for the next few years – but this is clearly good news that will move the effort one more step ahead.
Photo Credit: Julien HarneisShare on Facebook