Contagion, Viruses/Illnesses and Shedding
Contagion is the passing of a virus from one person to another through close contact. So when we “catch” a virus, such as measles, mumps or chickenpox we become contagious because we can pass it on to others. When we first become infected – or affected – by a virus we may not show any outward signs but we are still capable of passing the virus onto another person, then, in the case of measles or chickenpox, we develop a rash and now we know that we are contagious and can affect others. This is when we can choose to take the precaution of keeping ourselves or our children away from others.
Shedding is how the virus is passed from one person to another. While we are affected by a virus we shed that live virus in our body fluids. Some ways we can infect others with the virus are by coughing, sneezing, kissing, sharing cups, skin-to-skin contact, open wounds, urine or faeces. The amount of time that we shed the live virus for varies depending on the virus and the person.
There are several live virus vaccines including the MMR (measles/mumps/rubella) vaccine, the chickenpox vaccine and the oral polio vaccine. Anyone who has a live virus vaccine can shed the live virus from that vaccine in exactly the same way as the wild virus is shed. This means that anyone who has had a live virus vaccine can pass that virus on to another person, in other words they are contagious. This is known in the medical profession as seen when they tell people with compromised immune systems, such as those receiving chemotherapy, to stay away from anyone recently vaccinated.
So when we here about the outbreak of a virus such as measles of chickenpox, the big question is, “Is it caused by the wild virus or by the live virus in the vaccine?” The only way to know this would be to test for it in a laboratory but this is not done, so we do not know. The next question is, “Has the person infected by the virus recently been in contact with another person who has had a live virus vaccine?” Of course this is not so easy to establish as they could have met someone recently vaccinated in the shops or at school or anywhere. The other question to ask in an outbreak is, “Were the people who became infected by the virus vaccinated?” Because if they were then it means that their vaccine did not work. In the majority of cases those affected in an outbreak have been vaccinated.
The Emerging Risks of Live Virus & Virus Vectored Vaccines: Vaccine Strain Virus Infection, Shedding & Transmission – A Referenced Report from the National Vaccine Information Center by Barbara Loe Fisher Co-founder & President