The Emerging Risks of Live Virus and Virus Vectored Vaccinesreport on vaccine strain virus infection, shedding and transmission originally published by NVIC in November 2014.
Part I—Can People Receiving Live Virus Vaccines Transmit Vaccine Strain Virus to Others?Public health officials say that unvaccinated children pose a big danger to those around them and even threaten the health of fully vaccinated children and adults because vaccines can fail to prevent infection in vaccinated persons.1 2 3 4 Today, the most common argument used to justify “no exceptions” mandatory vaccination laws is that unvaccinated people pose a serious health threat to others who “cannot be vaccinated,” such as the immune-compromised.5 6
Some parents of unvaccinated children are asking the opposite question: Could my unvaccinated or immune compromised child get sick from coming in contact with a recently vaccinated person?
When it comes to live virus vaccines, the short answer is: Yes.
During a viral infection, live virus is shed in the body fluids of those who are infected for varying amounts of time and can be transmitted to others.7 8 9 Vaccine strain live virus is also shed for varying amounts of time in the body fluids of vaccinated people and can be transmitted to others.10 11 12
Although public health officials maintain that live attenuated virus vaccines rarely cause complications in the vaccinated person and that vaccine strain viral shedding rarely causes disease in close contacts of the recently vaccinated,13 it is important to be aware that vaccine strain live virus infection can sometimes cause serious complications in vaccinated persons and vaccine strain live viruses can be shed and transmitted to others with serious or even fatal consequences.
Many viruses have developed various molecular mechanisms to evade the immune responses of their host. There is great diversity among viruses and they often mutate and recombine with other viruses while continually being shed and transmitted in body fluids and waste products of animals and humans.14
There is an ongoing debate among scientists about where viruses came from and how they evolved and are still evolving.15 One virologist observed that replicating and mutating viruses are the “world’s leading source of genetic innovation:”
The huge population of viruses, combined with their rapid rates of replication and mutation, makes them the world’s leading source of genetic innovation: they constantly ‘invent’ new genes. And unique genes of viral origin may travel, finding their way into other organisms and contributing to evolutionary change.16Discussing the co-evolution of viruses with humans and other living organisms, another virologist wrote in 2012 that during epidemics viruses evolve. Genetic and environmental co-factors make some individuals more or less likely to die from or survive the infection, producing an increase of the numbers of resistant individuals in the population:
Viruses can become particularly dangerous when they evolve to acquire the possibility to infect new animal species. The defense systems of the new host may be generally unable to counteract the new pathogen and many individuals will die. In any epidemic, there are also individuals showing little sensitivity to or complete resistance to the particular pathogen. Both increased sensitivity and resistance to the infection are specified by the individual’s genetic makeup and various environmental factors. Accordingly, mass epidemics not only produce new virus variants but also alter the host population structure: highly sensitive individuals die, while the portion of resistant individuals in the population increases. Therefore, the coevolution of the virus and the host is a mutually dependent process.17
Viral Infections Both Trigger and Are Protective Against AutoimmunityMost people fear and view viruses as dangerous microbes that only cause sickness and death. However, emerging evidence has revealed that viruses play an integral role in helping us stay well, too.18
Healthy infants experience many different kinds of wild-type viral infections and shed virus without showing any clinical symptoms of illness. In addition to the protection they receive from maternal antibodies, viruses help the infant’s immune system develop and gives them early protection against more serious viral infections in infancy and later in life.19 20 21
Depending upon individual genetic variability, viral infections have been associated with the triggering of autoimmune disorders like type 1 diabetes in some individuals; however, for many other people viral infections appear to be protective against development of autoimmunity.22
Public Health Policies & the Hygiene Hypothesis: According to scientists discussing the ‘hygiene hypothesis,’ increased sanitation and public health interventions in modern societies have reduced the diversity of early experiences with viral and bacterial infections among infants and children and one negative outcome has been an increase in autoimmune and allergic diseases.23 They suggest that some infectious microbes, especially those that have co-evolved with humans, protect against a wide spectrum of immune-related disorders.24 25
The next article in this TVR series will be The Human Microbiome: Viruses R Us.