An announcement from the UN's World Health Organization on Saturday made it official: India is no longer on the list of polio-endemic countries.

On Jan. 13, India celebrated a full 12 months with no new cases of polio reported. And if they can remain polio-free for two more years, they will be formally considered to have eradicated the virus.

According to WHO Communications Officer Sona Bari, defeating this disease in India was no easy endeavor; a uniquely high level of cooperation between India's government and the UN was essential to success. One of the interesting things we did was put together a joint project called the National Polio Surveillance Project (NPSP), she said. It was a really strong partnership, even more so than when WHO typically goes in with technical support. This was really an agency under joint authority.

The NPSP was launched in 1997, so the WHO announcement reflects 15 years of progress. There were a couple of key challenges, said Bari. Dense populations, high poverty, very poor sanitation and infrastructure...It's the perfect storm for the virus. We saw very high transmission rates, and we found that the vaccine was less efficient in those settings than it had been in others. In response, a more targeted version of the vaccine was developed. The winning formula targeted only type-1 and type-3 versions of the virus, since type-2 wild polio had been eradicated worldwide.

The other challenge was recognizing that certain communities were overrepresented in terms of polio cases. We focused on coming up with a strategy that would target under-served communities, said Bari.

Migrant groups, for instance, were uniquely hard to reach. There are a large number of people who are constantly on the road, so we had to come up with strategies to anticipate their travel patterns, said Bari. NPSP set up vaccination centers in key areas and encouraged migrant communities to get the vaccinations wherever they could.

There are two methods of polio vaccination: inactive polio-virus vaccines (IPV), injected intravenously, and oral polio-virus vaccines (OPV). Both are effective, but OPV carries a slight risk of infecting the recipient since it does deliver a live--albeit attenuated--strain of the virus. OPV was used in India since it is more efficient and inexpensive in large cases like these. OPV is the vaccine that has stopped polio in most of the world, said Bari.

Polio primarily affects infants and young children.  It is highly infectious, which makes its containment a global challenge. It is caused by a virus that tends to enter the body orally and multiply inside the intestine before entering the nervous system. Many infected children do not suffer any symptoms, but those who do typically experience a spell of flu-like symptoms followed by temporary or permanent paralysis. There is no cure, but a vaccine can offer lifelong protection. WHO reports that since 1988, polio cases have decreased by over 99 percent. The disease was essentially eliminated in developed countries after the vaccine was developed in the 1950s.

Now that India has essentially eliminated the disease, only three countries remain on the polio endemic list: Afghanistan, Nigeria and Pakistan.

Right now, the two big challenges are Pakistan and some states in northern Nigeria. Those two are really crucial; that's where we're going to apply our strongest efforts, said Bari.

It's been a long war against a very difficult disease, but public health organizations seem to be winning battle after battle. Can we expect to see the end of polio all around the world? Yes, said Bari. Definitely within our lifetimes.