"Leaky" Vaccines

Interesting:

When people talk about the impact of vaccines, they usually mean the millions of humans saved from disease and death. But Andrew Read, an evolutionary biologist at Pennsylvania State University, University Park, likes to think about what vaccination does to pathogens. 

In 2001, he published a theory in Nature suggesting that some vaccines may cause viruses and bacteria to become more deadly. Now, Read has some evidence to back that up—at least in animals. 

A paper published in PLOS Biology this week suggests that widespread vaccination against Marek's disease, a viral infection in chickens, explains why it has evolved to become more lethal the past few decades. Something similar might happen with certain human vaccines, Read cautions. 

But other researchers say the study has little relevance for public health. Read “should stop scaremongering,” says vaccine researcher Adrian Hill of the University of Oxford in the United Kingdom. He and others worry that the paper—and news stories like this one—will only play into the hands of the antivaccine movement. 

Read's ideas are built on the widely accepted idea that pathogens often evolve to become less lethal over time. After all, killing their host quickly reduces their chances of being passed on, whereas causing mild symptoms, or none at all, should aid their spread. So-called leaky or imperfect vaccines, which don't prevent infection but merely reduce symptoms, upend that notion, Read argues. They allow the spread of deadlier pathogens that would normally burn out quickly. Leaky vaccines are common for animal infections, including Marek's disease. 

Most human vaccines, on the other hand, actually prevent infection, but that may soon change. With diseases like malaria or HIV, for which protection is very hard to achieve, researchers may settle for vaccines that save lives by preventing severe disease, but not infection. In the study, Read and his co-workers, working at the Pirbright Institute in Compton, U.K., showed that unvaccinated birds infected with highly virulent strains of Marek's disease didn't shed much virus; they also died too fast to pass the disease on to healthy, unvaccinated birds. But just as Read predicted, the opposite occurred in vaccinated birds: They shed more virus when infected with a virulent strain, readily infecting and killing unvaccinated cagemates. To Read, the result suggests that vaccines can favor strains that would otherwise be too lethal to spread. 

It's a convincing study, says Michael Lässig, who studies influenza evolution at the University of Cologne in Germany, “But it's a very special set of circumstances … I would be careful about drawing general conclusions.” Hill also thinks that Marek's disease may be a special case; nothing suggests that human vaccines have ever made a disease more virulent, he says. What's more, natural immunity is “leaky,” too, Hill argues, allowing infected people to survive and transmit a disease that is deadly to others. “For malaria, whatever today's vaccine does is a drop in the ocean of all the immunity that is happening in Africa from all the infections,” he says. 

Read suspects the phenomenon is more widespread. Feline calicivirus, which causes a respiratory infection in cats, also appears to have increased in virulence as a result of vaccination, Read says, and he is worried about the same thing happening with avian influenza, which some countries keep at bay with poultry vaccines. “You could have the emergence of super-hot strains,” he says. 

As for human disease, the study offers no support whatsoever for those who oppose vaccination, Read stresses. And if leaky vaccines are proven safe and effective, they should be used, he adds, but perhaps with closer monitoring and additional measures to reduce transmission, such as bed nets for malaria. “We need to have a responsible discussion about this.”

Definitely worth a discussion! But definitely true that natural immunity is leaky and can cause a similar effect. Why it happens with these few animal diseases is an interesting question.

"How one unvaccinated child sparked Minnesota measles outbreak"

CBS News:

A measles outbreak in Minnesota offers a case study of how the disease is transmitted in the United States today: An unvaccinated person travels abroad, brings measles back and infects vulnerable people -- including children who are unprotected because their parents chose not to vaccinate them.

That's the conclusion of a report published online June 9 in Pediatrics that details the 2011 outbreak that sickened 19 children and two adults in the state.

It began when an unvaccinated 2-year-old was taken to Kenya, where he contracted the measles virus. After returning to the United States, the child developed a fever, cough and vomiting. However, before measles was diagnosed, he passed the virus on to three children in a drop-in child care center and another household member. Contacts then multiplied, with more than 3,000 people eventually exposed.

Nine of the children ultimately infected were old enough to have received the measles-mumps-rubella (MMR) vaccine but had not.

In most of those cases, the child's parents feared the MMR vaccine could cause autism, according to researchers at the Minnesota Department of Health.

That idea -- first raised in 1998, by a British doctor named Andrew Wakefield -- has been discredited, said Pam Gahr, an epidemiologist who led the new research.

"But I think that as long as autism remains unexplained, the idea [that the MMR is a cause] will persist," Gahr said.

In the Minnesota outbreak, the child infected in Kenya was of Somali descent, as were most of the children whose parents had declined the MMR vaccine because of safety fears.

And that's consistent, Gahr said, with a striking decline in MMR acceptance among Minnesota's relatively large Somali population. In 2004, the number of Somali children in the state who were on schedule with their MMR topped 90 percent.

"By 2010, that was down to just 54 percent," Gahr said.

From what the health department learned in parent interviews, the decline seemed to stem from misinformation about an MMR-autism link.

Despite the unique circumstances of the Minnesota outbreak, though, measles can happen anywhere people are unvaccinated, said Dr. Andrew Pavia, chief of pediatric infectious diseases at the University of Utah in Salt Lake City.

"These outbreaks occur in all types of settings," said Pavia, who was not involved in the current study.

U.S. measles cases are at a 20-year high this year, the U.S. Centers for Disease Control and Prevention reported last week. As of May 30, the agency had received reports of 334 measles cases in 18 states.

Nearly all of the outbreaks involved unvaccinated people who brought measles back after a trip overseas, the CDC said.

The hardest-hit state is Ohio, where people in several Amish communities were infected after unvaccinated missionaries traveled to the Philippines and carried the measles virus back.

Amish communities have historically had low vaccination rates. And a 2011 survey of Amish parents who refused to vaccinate found that nearly all cited safety fears.

According to Pavia, the safety concerns of parents in the Minnesota outbreak illustrate the "power of bad information."

The MMR-autism link proposed by Wakefield was later found to be based on fraudulent data, and many studies since have found no connection between the vaccine and autism.

"Wakefield has been thoroughly debunked," Pavia said.

Gahr noted that these days, most parents never had or even saw a case of the measles. So some might dismiss it as just another childhood infection, she said.

But measles can prove serious, or even deadly. About 30 percent of people with measles develop a complication such as ear infection, diarrhea or pneumonia, the CDC says. Among children, one in 1,000 suffers brain inflammation, and one or two out of every 1,000 die.

"Even if you don't develop complications," Pavia said, "the disease is miserable."

Measles typically begins with a fever, cough, runny nose and "pink eye." After several days, a rash emerges around the face and neck, then spreads to the rest of the body.

"The thing is, we have the power to prevent it," Pavia said.

In the case of the Minnesota outbreak, he added, "the first infection that spread in the community was misinformation. The second was measles.

About that incidence of vaccine rejection in Somali US-born children... curious that this article doesn't mention anything about this:

A very interesting article was published today by Elizabeth Gorman on MinnPost.com that should be researched further: It might shine new light on genetic, and possibly environmental factors in autism.

The article reports that an unusually large proportion of Somali-speaking children in Minnesota have autism, something that has also been noted in Sweden, where Somali immigrants call autism "the Swedish Disease," because they did not see it back in East Africa.

According to the report, almost 6 percent of the Minneapolis school district's total enrollment is made up of Somali-speaking students. But in the city's early childhood and kindergarten programs, "more than 12 percent of the students with autism reported speaking Somali at home," and over "17 percent of students in the district's early childhood special education autism program are Somali speaking," the article said.

Somali kids with autism seem to be doing worse, on average, than their school mates: "About a quarter of all autism children who attend autism classrooms for students functioning too low to be mainstreamed in regular schoolrooms are Somali."

The statewide autism rate in Minnesota is already quite high -- at 100 per 10,000 children, as compared to the national average estimate of 67 per 10,000. In the Somali immigrant community, however, it could be much higher than either of those figures.

Why would that be? There is almost certainly a strong genetic connection at play here, but there may be other factors as well, including a lack of vitamin D from sunlight, (see the Swedish study in article) or, yes, vaccinations.

I do not know if vaccines are playing a role at all here. In fact, this report says that the Somali children were all born and vaccinated in the United States (though it seems to me that some must have immigrated here).

The "American Disease" idea comes from Somali parents themselves, and from some of the experts who work with them.

Anne Harrington, an early childhood special education coordinator for the Minneapolis school district and a specialist on the topic, told Gorman that Somalis "Are given more [vaccines] than we get, and sometimes they're doubled up. Then their children are given immunizations. In Somalia, their generations have not received these immunizations, and then suddenly they're getting just a wallop of them in the moms and then in the babies. That's certainly a concern that's been expressed to me by the Somali population."

I have never heard that before, and there may be nothing to it. On the other hand, the Centers for Disease Control and Prevention's Advisory Committee on Immunization Practices recommends that refugee adults receive at least 10 vaccines -- including pregnant women. Some of them contain thimerosal.

In addition, any of these kids who are older than five -- meaning they were born in 2002 or earlier -- could have received thimerosal in their vaccines.

Whatever the reason for the apparent higher rates of autism (ie, genes, sunlight, vitamins, vaccines, all of the above, none of the above) it is an interesting phenomenon and, it seems to me, an intriguing avenue of research.

There are data out there to suggest that elevated autism rates may not be limited strictly to immigrants from Somalia:

# A study of pervasive developmental disorder (a form of ASD) prevalence in Montreal school districts in 2003-2004 showed that the average PDD rate in the city's five predominantly French-speaking school districts (ie, largely Canadian-born) was 42.3 per 10,000 students, but in the largely English-speaking school district, where many immigrant children live, the rate was 69.2 per 10,000.

# In the English-speaking district, although the overall PDD rate was 69.2 per 10,000, among foreign-born children it was 106.6 per 10,000, and among Canadian-born children it was 67.6 per 10,000 - or 58% higher in the foreign born population.

# In Sweden, researchers reported that the incidence of autism among Somali immigrant children is far higher than among children living in Somalia (though better medical care and diagnostics would play a role, I'd think). Swedish media report that Somalis living in Sweden have dubbed autism, "The Swedish disease," because it is so common among Somali immigrants.

# These data might support reports that autism rates are also higher in immigrant communities in North America. On June 6, 2007, the Canadian Broadcasting News reported that, "autism rates are higher in immigrant families." Health-care specialists in Montreal, it said, were, "trying to understand why such a high number of autistic children come from immigrant families, a phenomenon seen in major cities across North America."

# This information MIGHT also help explain why autism numbers in California (and Minnesota, for that matter), are still high. In California, between 2003 and 2007, the rate of autism among black and white children enrolled in the state's DDS program increased by 50%. But the rate among Asian children in the same period went up by 79%, and the rate among Hispanic kids increased by 84.2%. The growth rate was about 58% higher among Asian and Hispanic children than black and white children.

# One in four California residents are foreign born. The majority are from Mexico, Central America, China, Korea, the Philippines and other countries with high vaccination rates (Mexico's is about 92%) and that still use the full amount of thimerosal in shots. Many if not most of these children are routinely revaccinated upon entry into the United States.

It would be very interesting, I believe, to look at autism rates in high and low immigration states. Not to implicate vaccines, but to find out if children of immigrants are more at risk than our native born population -- and why.

And:

Autism might not be any more prevalent among Somali-heritage children in Minneapolis than it is among white children in the city, but the severity of the developmental disorder appears harsher in this minority group.
In a much-anticipated report released Monday, University of Minnesota researchers found statistically similar rates of autism symptoms among 7- to 9-year-olds in Minneapolis, regardless of whether they were Somali or white. But all of the Somali-heritage children with autism also had related intellectual disorders — defined as scoring 70 or less on IQ tests — compared with a third of autistic children in the study overall.
“Somali children are much more likely to also have an intellectual disability, which means their symptoms, their characteristics, the ways in which autism presents itself in these children are very different,” said Amy Hewitt, the lead author of the study and a senior research associate in the university’s Institute on Community Integration.

Concerns about the prevalence of autism among Somali children surfaced among parents in 2008, and were validated in 2009 when a report from the Minnesota Department of Health found that Somali preschoolers were two to seven times more likely to receive autism services from the Minneapolis public school system.