I’m not talking about rates of vaccine exemptions here. Oh no. People like talking about vaccine exemption rates because it distracts them from the bigger issues of school vaccinations.

I’m talking about epidemiology.

The idea behind mandatory school vaccinations is to prevent diseases from spreading among children in a crowded setting. But required school vaccinations- especially for certain diseases- don’t necessarily solve the issue of transmission or serious outcomes. For example:

Measles/mumps/rubella/chickenpox

These are diseases that are generally mild in elementary school age children. I’ve written an extremely detailed post about measles, so I won’t regurgitate it here. (You can read it of you want references from the CDC and medical journals about how measles affects people of varying health and ages.) Long story short, measles is actually much more deadly in adults than children. Mumps is rarely deadly, however it can cause an infection of the testicles in teenage boys and men- though sterility is extremely rare. Rubella is generally a mild disease for children and contracting it in childhood confers lifelong immunity. But if a woman in her first trimester of pregnancy catches it, it can cause a condition called congenital rubella syndrome, causing the baby to be born with conditions like blindness, deafness or mental impairments. Chickenpox (varicella) is also much more severe in teens and adults. If a pregnant woman catches chickenpox, it might (in rare instances) cause birth defects. Also of note, in Great Britain, the National Health Service don’t recommend vaccinate for chickenpox on a regular basis because low circulation of the varicella virus can increase shingles in older adults.

Pertussis

I have also written a big post on pertussis/parapertussis as well and the relationship between vaccination and the adaptation of the bacteria. That’s where you can find all the nitty-gritty details and academic references on this subject. We are facing a growing crisis with asymptomatic transmission of pertussis. And even as more and more people are being vaccinated for pertussis, the rates keep climbing. See the CDC’s nice little chart here. Parapertussis is on the rise and pertussis vaccines are ineffective against it. So even if your kid’s whole class gets that ice cream party from 100% vaccine coverage, it won’t stop whooping cough. (But at least the kids got an ice cream party, right?)

Influenza

This one isn’t technically a school vaccine, though Ohio, New Jersey, Connecticut and Rhode Island require it for day care. The idea is probably to prevent transmission of the influenza virus to babies and toddlers since they (along with the elderly and the immunocompromised) are at the highest risk for complications. But you can’t actually achieve herd immunity with the flu vaccine because it’s only 40%-60% effective and herd immunity requires that 80%- 90% of a population be immune. And unfortunately the flu vaccine is less effective for children under 2 and adults over the age 65. Some studies measure flu vaccine effectiveness by how often people go to the hospital for flu- not necessarily in reduced cases of flu. In these types of studies, the flu vaccine is considered successful if you don’t get hospitalized for the flu after getting a flu shot. You may still get the flu, you may still pass the flu, but we long as you aren’t hospitalized for it, the vaccine can be counted as effective.

Hepatitis B*

Hepatitis B is primarily spread through injection drug use, sexual contact and maternal to child transmission during birth or the first few years of life. Child-to-child transmission is certainly possible, but it doesn’t happen very often.  (Just like hepatitis B from health care procedures is possible but doesn’t happen very often.) The age group at highest risk for HBV are adults who are opioid drug users and men who have sex with men. If we talk about Hepatitis B among children, teens are the most at risk with kids ages 15-19 having the highest rate of HBV infection. After that, it’s a pretty close tie between kids ages 10-14 and infants ages 0-4. That’s because 15-19 year olds are most likely to be participating in high risk behaviors with 10-14 year olds following behind. Kids ages 0-4 are mostly the maternal transmission cases where the mother passes the disease to the baby during birth or during the first few years of life. Kids ages 5-9 are the least likely to get hepatitis B because they aren’t sexually active, using drugs and aren’t in as close of contact with their mothers as infants.

However, children who contract hepatitis B are more likely become chronic carriers and develop liver cancer than adults who contract hepatitis B. So the idea behind vaccinating elementary school children for hepatitis B is to reduce the likelihood of child-to-child transmission- though the risk of becoming a chronic carrier seems to be highest among infants and children ages 1-5.

This is an interesting issue for most of the United States though because hepatitis B risk is relatively low in the US. 0.1%-0.5% of the population in the US are infected with the hepatitis B virus, in comparison to places like the Mediterranean where about 5% of the population is infected with hepatitis B virus and in many Eastern European countries, 8% or more of the population is infected.

Now countries that have sky-high rates of hepatitis B have much stronger requirements for hepatitis B vaccination. But in many countries like France, the UK, Denmark and Norway where hepatitis B infection rates are similar to the US, hepatitis B vaccination is focused on those children who are most at risk. Our American vaccine schedule for hepatitis B is more like that of high risk  countries like Greece, Slovenia, Slovakia, Hungary and Romania where hepatitis B is much more common. Within the US, our practice of requiring hepatitis B vaccination for elementary school children may not have a big impact on hepatitis B transmission- especially since child-to-child transmission in schools and day care centers since it is quite rare.

*Of course, not all of this applies to West Virginia which is seeing a dramatic increase in hepatitis B due to its high rates of injection drug use, though their rates have not yet approached that of the Mediterranean and Eastern Europe… Yet.

 

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