S & T

Updated: June 7, 2012 00:52 IST

Will the new type of oral polio vaccine be effective?

N. Gopal Raj
Comment (4)   ·   print   ·   T  T  
THE RATIONALE: Without the crucial protein, the virus in the vaccine under
development would not be able to produce viable progeny that could go on to
infect other cells. Photo: M. Karunakaran
THE RATIONALE: Without the crucial protein, the virus in the vaccine under development would not be able to produce viable progeny that could go on to infect other cells. Photo: M. Karunakaran

An oral polio vaccine strain that cannot revert to virulence is needed

Wouldn't it be nice to have a better sort of oral polio vaccine?

Widespread use of the oral vaccine has brought the eradication of polio tantalisingly within reach. Since 1988 when the world embarked on an effort to wipe out the disease entirely, the number of cases has fallen by 99.8 per cent.

Developed by an American scientist, Albert Sabin, the oral polio vaccine (OPV) uses weakened strains of the virus. The vaccine is easy to administer — simply put a couple of drops of it in a child's mouth. The viruses in the vaccine replicate in cells in the gut and evoke an immune response that protects the child when a wild virus comes along.

Nevertheless, the oral vaccine has a major drawback, one that could stand in the way of the total eradication of all polioviruses. As it multiplies in the gut, the mutations that weaken the virus can get reversed, giving rise sporadically to vaccine-derived strains that are as virulent as wild forms and spread as easily. In India, although no child has so far fallen victim to the wild virus this year, one has already been paralysed by a vaccine-derived strain.

Consequently, the endgame for polio eradication could well involve introducing inactivated polio vaccines (IPV), which use ‘killed' viruses that cannot replicate and therefore carry no risk of turning virulent again. But IPV has its own problems, including higher cost and the fact that it has to be injected.

An oral polio vaccine strain that has been further crippled so that it cannot revert to virulence is therefore an attractive proposition.

Recently, Hyderabad-based Ella Foundation received a grant from the ‘Grand Challenges Explorations' initiative of the Bill & Melinda Gates Foundation to develop just such a vaccine strain.

The Ella Foundation is an independent scientific and industrial research organisation with a focus on research in infectious diseases. It was established by Krishna Ella and his wife, Suchitra Ella, who started the biotechnology company, Bharat Biotech International, which makes a variety of vaccines and biotherapeutics.

Scientists of the Foundation would, according to information given on the Grand Challenges Explorations web site, “develop and test for use in a vaccine a live single-cycle poliovirus that has been modified to eliminate the gene essential for replication. This highly disabled virus will be tested for its immunogenicity and its inability to re-emerge as vaccine-derived poliovirus.”

No replication

In a review paper published in 2006, U.S. scientists Tim Dudek and David Knipe, outline how it might be possible to create replication-defective viruses that could be used in vaccines.

Such mutant viruses would possess the advantages of both classical types of viral vaccines, i.e. those using inactivated viruses and ones based on attenuated strains, they noted.

The paper notes that by manipulating the viral genome, mutant versions could be made that lack a key protein needed for successfully completing its replication cycle in a cell. The mutants are then propagated in cell lines that supply the missing protein.

If such mutated strain could be successfully created for polio, the idea is that, given as an oral vaccine, the viruses would infect intestinal cells and go through its replication cycle just once.

But without the crucial protein, these viruses would not be able to produce viable progeny that could go on to infect other cells.

According to information provided by the Ella Foundation's public relations agency, more experiments were needed before deciding which poliovirus gene (or genes) would be deleted.

“The idea is full of holes,” exclaimed Vincent Racaniello, Higgins Professor of Microbiology and Immunology at Columbia University in the U.S., who has worked a great deal on the poliovirus.

“First and foremost, if you are delivering a polio vaccine orally, I suspect that it has to replicate,” he pointed out in an email.

The big question

It would be straightforward to delete a poliovirus gene and make a stock of the mutant virus. The question was what sort of immune response it would elicit after being given orally.

Even if the mutant strain was taken up by gut cells, without viral replication and in the absence of immune-boosting chemicals known as adjuvants, “it would not make a robust immune response.”

Although many replication-defective viral vaccines are being tested, particularly against HIV, none have yet been licensed for use in humans, said Dr. Racaniello in his email.

The article brings into conversation an important discussion that public health personalities in India do not admit. Children should be monitored after the vaccine and preventive should be taken immediately. Unfortunately the second part is not carried out in our country. Since we are a polio endemic country and humans are only host for polio virus the aim is to completely get rid of the wild type polio virus from the environment by preventing it from colonization. Therefore the OPV is needed to be given to every children to eradicate polio. As with countries that got rid of polio, they have shifted to IPV vaccines. While generation of new vaccine with fewer side effects is always noble idea it totally foolhardy to make the comments like Sabin vaccine is only being used for the reason that it is easy to administer. There are possibilities too like use of a combination of IPV and OPV and others.

from:  Arnab Basu
Posted on: Jun 8, 2012 at 03:27 IST

The oral Polio vaccine was created by Dr Jonas Salk an American Doctor. The Salk
vaccine was banned in the US after a congressional enquiry in 1978 which
determined that all the 76000 cases of Polio which occured in 1976 in the US were
due to the oral Vaccine.
Polio has now been eradicated in the US & Europe with the Sabin Vaccine which is an inactivated Injectible vaccine. Upto the 1980's The Sabin vaccine was the only vaccine permitted to be used in India. It is interesting that the oral Salk Vaccine was only introduced in India after being banned in the US. A major drawback of the oral Salk vaccine is that being a live virus it causes in polio in children who are immuno compromised. In India there is a lot of malnutrition and tuberculosis. These children have a low immunity already. Are we justified in giving them the oral polio vaccine knowing that it can cause them to get polio? The poor cannot afford the treatment for polio. To prevent polio give them Sabin Vaccin

from:  Dr Manik Hiranandani
Posted on: Jun 7, 2012 at 20:46 IST

can any body explain this article properly? there are too much technical
terms associated with it. if any body can pls.

from:  abhishek
Posted on: Jun 7, 2012 at 19:27 IST

Both Salk and Sabine regretted the polio vaccines they introduced for their propensity to cause polio. Vaccines are given to healthy children and so any adverse effect should not be tolerated. The OPV causes 500 to 600 polio cases per year in India alone. There is also the vaccine strain virus that has attained virulence and is causing
polio. It has also caused cases of Acute Flaccid Paralysis (AFP), a
condition indistinguishable from polio, to surge to 47,500 cases per
year, again in India alone. The presence of monkey viruses in these
vaccines are a cause for great concern as the only one studied (the SV
40) was found to be intensely tumerogenic and carcinogenic. Doctors of
India have questioned the spurt of encephalopathy cases in children in
those areas where the OPV has been administered extensively. What is
not discussed is, as the viruses in the vaccine recipient are shed
through stools, others (even adults)may catch polio.

from:  Jagannath Chatterjee
Posted on: Jun 7, 2012 at 16:42 IST
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