A single-injection vaccine for the polio virus

A new nanoparticle vaccine developed by MIT researchers could assist efforts to eradicate polio worldwide, according to a study published in the journal Proceedings of the National Academy of Sciences. The new vaccine developed an injectable microparticle formulation of the inactivated polio vaccine (IPV) that releases multiple pulses of stable antigen over time. The vaccine delivers multiple doses in just one injection which will make it easier to immunize children in remote regions where the disease still exists.

Although the number of reported cases of polio dropped by 99 percent worldwide between 1988 and 2013, according to the Centers for Disease Control, but the disease has not been completely eradicated, because of the difficulty in reaching children in remote areas to give them the two to four polio vaccine injections required to build up immunity.

To create a single-injection vaccine, the MIT team encapsulated the inactivated polio vaccine in a biodegradable polymer known as PLGA. This polymer can be designed to degrade after a certain period of time, allowing the researchers to control when the vaccine is released.

There's always a little bit of vaccine that's left on the surface or very close to the surface of the particle, and when it is put inside the body, whatever is at the surface just diffuses away. This is called the initial burst. The particles then sit at the injection site and over time, as the polymer degrades, they release the vaccine in bursts at defined time points, based on the degradation rate of the polymer.

Earlier the researchers had to face one major obstacle that had hindered the efforts to use PLGA for polio vaccine delivery. The polymer breaks down into byproducts called glycolic acid and lactic acid, and these acids can harm the virus so that it no longer triggers the right kind of antibody response.

To prevent this, the MIT team added positively charged polymers to their particles. These polymers act as "proton sponges," sopping up extra protons and making the environment less acidic, allowing the virus to remain stable in the body.

In the PNAS study, the researchers designed particles that would deliver an initial burst at the time of injection, followed by a second release about 25 days later. They injected the particles into rats, then sent blood samples from the immunized rats to the Centers for Disease Control for testing. Those studies revealed that the blood samples from rats immunized with the single-injection particle vaccine had an antibody response against poliovirus just as strong as, or stronger than, antibodies from rats that received two injections of Salk polio vaccine.

To deliver more than two doses, the researchers say they could design particles that release vaccine at injection and one month later, and mix them with particles that release at injection and two months later, resulting in three overall doses, each a month apart. The polymers that the researchers used in the vaccines are already FDA-approved for use in humans, so it is more likely to be tested in clinical trials in near future.

Going a step further the researchers are also working on applying this approach to create stable, single-injection vaccines for other viruses such as Ebola and HIV.

There are no drugs against poliovirus, and in about 1 percent of cases, it enters the nervous system, where it can cause paralysis. The first polio vaccine, called the Salk vaccine, was developed in the 1950s. This vaccine consists of an inactivated version of the virus, which is usually given as a series of two to four injections, beginning at 2 months of age. In 1961, an oral vaccine was developed, which offers some protection with only one dose but is more effective with two to three doses.