Parents choosing not to vaccinate are often made to feel like bad citizens, placing the safety of their own children above that of the community as a whole. Agreeing to vaccination with all its attendant risks, so the rationale goes, is taking one for the herd by helping to lower the risk of infectious disease for all.
But the latest evidence shows that certain forms of vaccines may actually put society at greater risk by allowing mutations of more virulent forms of disease.
Vaccinations that don't prevent the spread of pathogens are often referred to as 'leaky' vaccines because they allow for the evolution of 'hotter' pathogens. Far from being protective, leaky vaccines put unvaccinated individuals at greater risk by exposing them to 'ninja' viruses.
Researchers led by a team from Penn State University in Pennsylvania discovered precisely this with a vaccine that had been developed to protect the poultry population from the herpesvirus that causes Marek's disease in chickens, caught by inhaling dust contaminated with the virus shed from the feather follicles of infected birds.1
Poultry farmers rely on such vaccines because once a poultry house is contaminated, chicks can get infected soon after hatching and remain infectious for life.
In the 1950s before a vaccination was introduced, Marek's disease was a minor disease causing a mild form of paralysis and, only rarely, death. Now, after the introduction of a vaccine, the team has discovered that the disease has evolved to cause cancers in a wide range of organs and is capable of killing all unvaccinated birds in as little as 10 days.
In one of five experiments, the researchers mixed vaccinated with unvaccinated birds together, injecting the vaccinated chicks with several strains of vaccines. Later, by analyzing both sets of birds and then measuring the concentration of virus genomes in the dust of the cages containing the chicks, they discovered that vaccination greatly increased the infectious period of the hottest strains of the virus, increasing the total amount of virus shed by several orders of magnitude.
"The net effect of vaccination," concluded the study, "... was to vastly increase the amount of virus shed by virulent strains into the environment."
The scientists then co-housed birds infected with the three most virulent strains with chickens that were not vaccinated; all unvaccinated birds infected by the two most lethal strains were dead within 10 days.
Ordinarily, in nature, the most virulent forms of disease don't spread so rapidly because pathogens that are so 'hot' or virulent will kill their hosts-and therefore themselves. But vaccines like this create a 'leaky' barrier against the virus because vaccinated individuals survive and constantly shed the virus into the environment, where it continues to evolve.
"Vaccination enabled the onward transmission of viruses otherwise too lethal to transmit, putting unvaccinated individuals at great risk of severe disease and death," stated the report.1
"When a vaccine works perfectly . . . it prevents the vaccinated from being sickened by the disease and it also prevents them from transmitting the virus to others," said Venugopal Nair, head of the Avian Viral Diseases programme at the Pirbright Institute in Woking, who led the UK arm of the study.
In this instance, the vaccines are designed to mimic the immunity that animals and humans naturally develop after contracting and surviving viral diseases. "Our research demonstrates that another vaccine type allows extremely virulent forms of a virus to survive-like the one for Marek's disease in poultry," Nair said.
Leaky avian flu vaccines
There's a similar situation with avian flu. "The most virulent strain of avian influenza now decimating poultry flocks worldwide can kill unvaccinated birds in just under three days," says Andrew Read, Evan Pugh Professor of Biology and Entomology and Eberly Professor in Biotechnology at Penn State, lead author of the study. And rather than culling the herd, the vaccination used in Southeast Asia is leaky, and so is only creating a worse form of the disease.
Scientists like Read believe that the human vaccines now in use do not mutate. Nevertheless, he is concerned that we are entering an era of 'second-generation vaccines' that are decidedly leaky-such as those for malaria and HIV-and which simply propagate more deadly forms of disease.
"It is critical," he said, "that we determine that vaccines being developed for the Ebola virus are not leaky, so that it doesn't evolve into something even more deadly." It's also critical, he says, that people get vaccinated to protect themselves against the even more dangerous diseases being created by leaky vaccines.
New diseases from vaccines
Read's view-that our present human vaccines are not leaky-is not borne out by the research. Getting jabbed with a weakened or killed version of a virus can cause you to develop a viral 'mutant' or encourage its spread in the population at large, a situation that has already happened with several types of vaccine.
In the 1960s, when US Army recruits were given an experimental killed pneumonia vaccine, the vaccine caused unpredictable shifts in virus type. Epidemics of disease from these mutant viruses occurred among recruits, rendering the vaccine useless and sending the scientists scurrying back to the laboratory to develop a vaccine that would knock out the mutations as well.2
It has been estimated that 3 per cent of babies born to mothers given the hepatitis B vaccine go on to develop a mutated form of hepatitis B virus (HBV).3 In one study of a group of babies born to HBV-positive mothers and given a full immunization programme against the virus, one in 60 became HBV-positive, and one in 80 showed they had a viral mutant of the vaccine. This mutant has been associated with hepatitis and active liver disease.4
In another study, patients vaccinated with the HepB vaccine had a mixture of these mutants and the usual form of HBV, as well as mild hepatitis. But those patients whose blood contained the mutant on its own eventually suffered more severe liver disease.5
The other problem with mutant viruses is that they often aren't detected on blood-donor screening, which means this new form of hepatitis could be transmitted through blood transfusions. And, of course, the virus may infect individuals even if they've been vaccinated.
All of which suggests that by messing with Mother Nature and natural selection with imperfect vaccines, medicines may just be aiding the conversion of mutant pathogens viruses into true ninjas-stealth viruses that are silent but deadly.
Eradicating one strain of a virus can also encourage other forms of it to proliferate. This is precisely what's happening with the Haemophilus influenzae type b (Hib) meningitis vaccine. As b-type H. influenzae strains are being wiped out by vaccination, mutant non-b strains are thriving.1
One study looked at 408 strains of H. influenzae isolated from various diseases. Although 94 per cent were type b, the rest were 'non-serotypable' (NST) strains. The authors predicted that, as more Hib vaccine is used, NST strains would be causing more middle-ear infections, sinusitis, chronic bronchitis and other, mostly respiratory, infections.2
Connections have also been made between the increasing prevalence of penicillin-resistant pneumococcal meningitis and universal Hib vaccination.3
As WDDTY columnist Harald Gaier once put it: "Trying to eradicate viruses through vaccination is like squeezing a balloon. Squeeze one part of it, and another form of it just pops out."
1 PLoS Biol, 2015; 13: e1002198
2 Ginsberg HS, ed. The Adenoviruses. New York: Plenum Press, 1984
3 J Biomed Sci, 2001; 8: 237-47
4 Lancet, 1990; 336: 325-9
5 Gastroenterology, 1992; 102: 538-43