Posted at 10:50 a.m., Friday, March 15, 2002                                                                                                                                                       Study finds on Carribbean polio

By Paul Recer, AP Science Writer

WASHINGTON - When a vaccine containing a live virus collided with a population that was poorly immunized, an outbreak of polio (news - web sites) resulted among children in Haiti and the Dominican Republic, according to a new study.

Even though Haiti and the Dominican Republic, which share the island of Hispaniola in the Caribbean, were declared polio-free in the 1980s, both countries reported cases of the paralyzing disease in the summer of 2000.

Thirteen children were infected in the Dominican Republic and there were eight cases, including two deaths, in Haiti.

Teams from the Centers for Disease Control and Prevention (news - web sites) and the Pan American Health Organization quickly responded, with disease detectives looking for the source of the disease.

In a study appearing Friday in the electronic version of the journal Science, researchers report that they found the new cases of polio originated from the modified polio virus that was used in the oral vaccine, which is usually given on sugar cubes.

Olen M. Kew of the CDC, first author of the study, said that the outbreak resulted from unprotected children coming in contact with children who had received the oral vaccine.

Patients given the oral vaccine develop a mild form of polio that results in an immunity to the disease. When this happens in a population that has not been inoculated, there is a chance that others may get the disease, said Kew.

"The virus normally does not spread from person to person if the community has a high vaccine coverage," said Kew. "In Haiti, after the wild-type polio virus had been eradicated, the only source was through the polio vaccine."

He said that there was a false sense of security in Haiti because natural polio had been wiped out. As a result, the immunization efforts were relaxed. In some villages, the rate of polio vaccination had been allowed to drop to about 7 percent. That primed the children for an outbreak of from the oral vaccine.

In the United States, oral polio vaccine causes only rare, isolated cases of polio because immunization against the disease in the general population is very high, about 90 percent.

Kew said that in Haiti and the Dominican Republic, after the introduced polio virus infected some in the poorly immunized population, it mutated and became even more virulent.

The outbreak was quickly ended with major immunization drive that pinched off the polio spread and protected the population, but the experience taught public health officials a lesson about the disease, said Kew.

"We've got a wake up call that said you've got to maintain a high level of immunization in order to be safe," he said.

Concerns about giving some rare patients polio led the CDC, the American Academy of Family Physicians (news - web sites), the American Academy of Pediatricians and others to recommend that children be treated with injectable polio vaccines made with killed virus instead of the oral vaccine made with the modified live virus.

Dr. Thomas N. Saari, a professor of pediatrics at the University of Wisconsin School of Medicine, said that the Hispaniola study "points to the wisdom" of switching to the injectable polio vaccine.

"Rare individuals who took the oral vaccine can harbor the strain over a long period of time, something that doesn't happen with the injectable," he said.

Kew said that in the developing world the oral vaccine still is used because of the lower cost and the scarcity of trained personnel required to distribute injected vaccines.

He said as part of an international effort to eradicate polio, medical teams have conducted massive oral polio vaccination drives that immunize a whole population in a community within a short time. For instance, said Kew, 100 million people were immunized in India in one day — and the effort was repeated a month later.

When so many people are inoculated at once, said Kew, the chances of outbreaks from the oral polio vaccine are unlikely.

                                                                                                                                                                                         Posted at 9:21 p.m., Thursday, March 14, 2002

Carribbean has polio outbreakBy

Paul Reger, Ap Science Writer

WASHINGTON (AP) - An outbreak of polio (news - web sites) in Haiti and the Dominican Republic has been traced to a weakened virus in a vaccine that mutated and spread disease among poorly immunized children.

Even though Haiti and the Dominican Republic were declared polio-free in the 1980s, both countries reported cases of the paralyzing disease in the summer of 2000. The countries share the Caribbean island of Hispaniola.

Thirteen children were infected in the Dominican Republic and there were eight cases, including two deaths, in Haiti. Teams from the Centers for Disease Control and Prevent and the Pan American Health Organization quickly responded, with disease detectives looking for the source of the disease.

In a study appearing Friday in the electronic version of the journal Science, researchers report that they found the new cases of polio originated from the modified polio virus that was used in the oral vaccine, which is usually given on sugar cubes.

Olen M. Kew of the CDC, first author of the study, said the outbreak resulted from unprotected children coming in contact with children who had received the oral vaccine.

Patients given the vaccine develop a mild form of polio that results in an immunity to the disease. When this happens in a population that has not been inoculated, there is a chance that others may get the disease, Kew said.

"The virus normally does not spread from person to person if the community has a high vaccine coverage," Kew said. "In Haiti, after the wild-type polio virus had been eradicated, the only source was through the polio vaccine."

He said there was a false sense of security in Haiti because natural polio had been wiped out. As a result, immunization efforts were relaxed. In some villages, the rate of polio vaccination had been allowed to drop to about 7 percent. That primed the children for an outbreak of from the oral vaccine.

In the United States, oral polio vaccine causes only rare, isolated cases of polio because immunization against the disease is very high, about 90 percent.

Kew said that in Haiti and the Dominican Republic, after the introduced polio virus infected a poorly immunized population, it mutated and became even more virulent.

The outbreak was quickly ended with major immunization drive that pinched off the polio spread and protected the population, but the experience taught public health officials a lesson, Kew said. "We've got a wake up call that said you've got to maintain a high level of immunization in order to be safe," he said.

Concerns about giving some patients polio led the CDC, the American Academy of Family Physicians (news - web sites), the American Academy of Pediatricians and others to recommend that children be treated with injectable polio vaccines made with killed virus instead of the oral vaccine made with the modified live virus. Dr. Thomas N. Saari, a professor of pediatrics at the University of Wisconsin School of Medicine, said that the Hispaniola study "points to the wisdom" of switching to the injectable polio vaccine. "Rare individuals who took the oral vaccine can harbor the strain over a long period of time, something that doesn't happen with the injectable," he said.

Saari, who serves on a committee at the American Academy of Pediatrics, said the study also showed the importance of a nation maintaining a high level of immunization.

"The main thing that prompted the outbreak (in Hispaniola) was the low rate of coverage," he said. Kew said that in the developing world the oral vaccine still is used because of the lower cost and the scarcity of trained personnel required to distribute injected vaccines.

He said as part of an international effort to eradicate polio, medical teams have conducted massive oral polio vaccination drives that immunize a whole population in a community within a short time. For instance, Kew said, 100 million people were immunized in India in one day — and the effort was repeated a month later. When so many people are inoculated at once, said Kew, the chances of polio outbreaks are unlikely.

Dr. Neal A. Halsey of the Johns Hopkins Bloomberg School of Public Health said the experience in Hispaniola shows that developed countries need to vigorously assist poor countries in maintaining high levels of vaccination and disease control. "We can't ignore these problems," he said, "because what happens there can pose a risk to the rest of the world."

                                                                                                                                                  Vaccine confirmed as source of polio outbreak

By Amy Norton NEW YORK (Reuters Health) - A recent outbreak of the paralyzing viral infection polio in Haiti and the Dominican Republic has been traced to a strain of oral polio vaccine (OPV) that mutated back to virulence, according to international health officials.

Based on genetic analysis of viral samples, they believe the outbreak, which struck nearly two dozen children in both countries between 2000 and 2001, arose from OPV given to one child in 1998-1999.

Health officials had already cited the vaccine as the probable source of the outbreak, but this new analysis now makes it "unequivocally clear," research leader Dr. Olen Kew, of the US Centers for Disease Control and Prevention (news - web sites) (CDC) in Atlanta, Georgia, told Reuters Health.

Their findings were published Thursday in Sciencexpress, the online edition of the journal Science.

Poliovirus spreads from person to person, usually going unrecognized because it produces mild symptoms or none at all. When it attacks nerve cells, however, the infection can cause crippling, sometimes deadly, disease.

OPV contains a live, weakened polio virus that is very effective at conferring immunity to the infection. But it can, in rare cases, cause polio. For this reason, countries such as the US now use only inactivated polio vaccine (IPV), which is injected.

OPV continues to be the standard in developing countries, however, because it is cheaper and easier to administer, doesn't require supplies of sterile needles and is more effective than IPV at preventing outbreaks.

But the cases in Haiti and the Dominican Republic illustrate a potential risk with OPV when it is given in a population where many people are unvaccinated. After a person receives OPV, virus from the vaccine is shed in the stools for a short period of time. In this outbreak, shed virus from a single OPV dose spread and mutated back to a virulent state, causing paralytic disease in a group of children who had either not been vaccinated or had not received a complete course of OPV.

This same scenario has been blamed in a number of cases of paralytic disease in Egypt and the Philippines. According to the researchers, one of the critical factors in all of these outbreaks was the large number of unvaccinated, vulnerable people in the population.

In fact, Kew explained, it is common for OPV strains to "back-mutate." It only becomes a potential problem in populations with low vaccination rates, which lack a "wall of immunity."

He said the findings underscore the importance of improving vaccine coverage in areas such as Hispaniola, the island that comprises Haiti and the Dominican Republic. They also emphasize the need to eradicate wild-type poliovirus "as soon as possible," Kew and his colleagues note.

If eradication happens, public health officials could phase out the use of OPV, in favor of IPV. Officials are currently trying to develop an "end-game strategy" for going about this, said the CDC's Dr. Mark Pallansch, a co-author on the study.

However, he noted, an "emergency stockpile" of OPV would be kept on hand in the event of a polio outbreak.

SOURCE: Sciencexpress 2002;10.1126/science.1068284.

                                                                                                                                                   Polio in Haiti linked to incomplete vaccination

Maggie Fox, Health and Science Correspondent WASHINGTON (Reuters) - Incomplete vaccination against polio (news - web sites) in Haiti and the Dominican Republic allowed the crippling virus to mutate, escape and then infect 21 people, killing two children, researchers said on Thursday.

They said world health officials need to get to work vaccinating children against polio, which is virtually eradicated in most parts of the world.

"The outbreak probably began in Haiti, when a routine oral poliovirus vaccine dose was given to a child living in a community with low vaccine coverage," the researchers, led by Olen Kew of the U.S. Centers for Disease Control and Prevention (news - web sites), wrote in their report.

One of those who died was a 12-year-old boy and another was a boy just 35 months old. "He didn't see his third birthday," Kew said. "If they had only used the vaccine appropriately, this would not have happened."

Two factors are to blame for the outbreak, the researchers wrote in this week's issue of the journal Science. One is the low vaccination rate in Haiti and the Dominican Republic, which share an island in the Caribbean. "

Low population immunity was the key risk factor," Kew said in a telephone interview.

"In Haiti, reported coverage rates for three doses of oral poliovirus vaccine for children under one year of age were the lowest in the Americas, falling to around 30 percent nationwide from 1992 to 1997 and remaining below 60 percent by 2000," the researchers wrote.

In the affected Dominican Republic communities only between 20 and 30 percent of people were vaccinated.

The World Health Organization (news - web sites) wants to eradicate polio globally, but says the effort has been hampered by a lack of funds and political will in the affected countries. In the United States, polio killed thousands of people and disabled tens of thousands before it was wiped out in 1979.

In Haiti, political strife and poverty have interfered with vaccination efforts, Kew said.

The second factor was the use of an oral vaccine, which uses a live but weakened strain of the virus. The oral vaccine, developed by Albert Sabin, helped rid many countries of polio, including the United States, because it is so easy to give and is highly effective.

But the virus used in the vaccine is still alive, although it has been altered so it does not cause disease.

VIRUS TO VIRUS DATING SERVICE

It stays alive in the body, and it turns out, it can hook up with other, related viruses called enteroviruses. They swap DNA and the polio virus can become deadly and highly infectious again. It is shed in the feces and gets into the water supply.

People get polio from infected water, so when sewage gets into drinking or washing supplies, the newly energized polio virus can infect them with crippling effects.

Kew said the study shows the importance of getting everyone vaccinated, as the few vaccinated children were, in essence, infecting everyone else.

"Even in developed countries, when people don't vaccinate their kids, the virus can find them," Kew said.

Most people infected with polio have no symptoms. But in a small percentage of cases, the virus attacks the nerves -- usually the spinal cord -- and can paralyze the victim. Between two to five percent of children with paralytic polio die and up to 30 percent of adults.

Humans are the only animals that can be infected with polio, so health officials think vaccination can wipe it out, like smallpox was eliminated in 1978.

There is another vaccine, the inactivated poliovirus vaccine based on one invented by Jonas Salk. This injected vaccination is now widely used because the virus is killed and cannot become dangerous again.

But people who receive the injected vaccine can become infected with wild polio and, while they do not become sick, can spread it.

Kew and colleagues noted that outbreaks of polio have been traced to the oral vaccine not only in Haiti and the Dominican Republic, but in the Philippines and Egypt.

But they stressed that the oral vaccine is still useful, not least because it works better.

"We don't want people to jump to the conclusion that inactivated polio vaccine (the injected version) is the answer," Kew said.