Unvaccinated children aren't only at risk themselves—if too few people receive their vaccinations, the protection of "herd immunity" can be threatenedby Kelly Oakes / March 19, 2019 / Leave a comment
“No vaccine, no school” is how Italy’s health minister described a new law that came into force in the country last week.
In an effort to increase poor vaccine uptake, children under six will now be turned away from nursery if parents can’t prove they’ve had a range of mandatory vaccinations, including those for chickenpox, polio, measles, mumps, and rubella. While older children can’t be banned from school, parents can be fined up to €500 if they send their child in unvaccinated.
Measles vaccination rates in Italy reached as low as 80 per cent in some areas in 2017, when the law was introduced, and the number of children contracting the disease in April 2017 was ten times higher than it had been a year before.
Vaccination rates as low as 80 per cent are worrying—and not just for those children that go unvaccinated. The World Health Organisation says a rate of 95 per cent is needed in order to protect the population as a whole and stop outbreaks of diseases like measles.
That figure provides what’s known as “herd immunity”: the idea that, when enough people in a population are protected through a vaccine, that protection extends to others who have not been vaccinated. It works because vaccines don’t just provide you with individual protection against a disease, they also stop you spreading it.
If someone brings measles into a group of unvaccinated people it could spread to everyone, who would in turn pass it on to all the people they come into contact with, and so on. On the other hand, if all of the people someone carrying measles comes into contact with are vaccinated, it won’t get passed on and will find it much harder to spread.
Those who can’t be vaccinated because they’re either too young or don’t have a strong enough immune system rely on herd immunity to keep them safe. But it doesn’t take a huge dip in vaccination levels for the effect to drop off.
The vaccination rate required to keep a disease contained depends on how contagious it is. The key is to make sure each person passes it on to less than one other person, on average. Say someone with chickenpox spreads it to ten other people—to prevent an…