Single-injection vaccine for polio virus developed

MIT scientists have developed a new nanoparticle vaccine that could assist efforts to eradicate polio worldwide.

The vaccine, which delivers multiple doses in just one injection, could make it easier to immunise children in remote regions of Pakistan and other countries where the disease is still found.

While the number of reported cases of polio dropped by 99 per cent worldwide between 1988 and 2013, according to the US Centers for Disease Control, the disease has not been completely eradicated, in part 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.

"Having a one-shot vaccine that can elicit full protection could be very valuable in being able to achieve eradication," said Ana Jaklenec, a research scientist at Massachusetts Institute of Technology (MIT) in the US.

"We are very excited about the approaches and results in this paper, which I hope will someday lead to better vaccines for patients around the world," Langer said.

There are no drugs against poliovirus, and in about one per cent of cases, it enters the nervous system, where it can cause paralysis. The first polio vaccine, also 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.

The oral vaccine, which consists of a virus that has reduced virulence but is still viable, has been phased out in most countries because in very rare cases, it can mutate to a virulent form and cause infection.

It is still used in some developing countries, however, because it is easier to administer the drops than to reach children for multiple injections of the Salk vaccine.

For polio eradication efforts to succeed, the oral vaccine must be completely phased out, to eliminate the chance of the virus reactivating in an immunised person.

"The goal is to ensure that everyone globally is immunized. Children in some of these hard-to-reach developing world locations tend to not get the full series of shots necessary for protection," Ana Jaklenec, a research scientist at MIT.

To create a single-injection vaccine, researchers 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.

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, and found that the blood samples had an antibody response against poliovirus just as strong as, or stronger than, antibodies from rats that received two injections of Salk polio vaccine.

Researchers said that they could design vaccines that deliver more than two doses - each a month apart.

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