Let's look at the status quo and ongoing debate regarding vaccine coverage and exemptions
By receiving the MMR (measles, mumps and rubella) vaccine an individual does not just protect themselves against measles, they also prevent the spread of the disease to other people in their community. Due to this indirect effect, a community can be effectively protected against measles even if not all of its members have been vaccinated. This is known as herd immunity and it is crucial for the protection of individuals who cannot receive the vaccine, such as babies under 12 months of age, individuals with immune-suppressing diseases and people with vaccine allergies. The threshold, or minimum percentage of immune individuals needed to establish herd immunity, for measles is estimated to be 93%-95%. This is higher than other infectious diseases such as polio where the threshold is 80%-86%. Learn more here.
This grid map shows the estimated percentage of kindergardeners enrolled during the 2018-2019 school year who had received the MMR vaccine. Only the states shaded with the lightest two colors have surpassed the herd immunity threshold for measles (using the more conversative target of 95% coverage). Based on data from the Centers for Disease Control and Prevention. No data available for Washington DC, New Jersey and Alaska.
These gaps in vaccine coverage may seem surprising given the fact that all US states have laws which require children to have certain vaccines as a prerequisite for entry into daycare and kindergarden. However, all 50 states allow for medical exemptions from this requirement. Most states (45 states and Washington DC) also grant religious exemptions and 15 states allow philosophical exemptions based on other non-religous personal or moral beliefs. The recent US measles outbreaks have ignited a debate about whether such vaccine exemptions should be abolished or at least restricted. Learn more here.
This grid map shows the estimated percentage of kindergardeners with an exemption for any vaccine during the 2018-2019 school year based on data from the Vaccination Exemptions Reports by the Centers for Disease Control and Prevention. No data available for Washington DC. Both visualization adapted from D3 block by Gerald Rich. Learn more about the art of choosing a grid map.
In both visualizations darker colors represent greater risks regarding vaccine coverage. Idaho, for example, has both a relatively low MMR vaccine coverage rate (in the 87%-89.7% range) and a relatively high vaccine exemption rate (above 6.8%). However, this comes with the caveat that most US states do not break down their vaccine exemption statistics by type of vaccine. Therefore, the data for the second visualization only approximates MMR vaccine exemption rates. Even if we assume that all vaccine exemptions obtained include MMR exemptions, vaccine exemptions alone cannot explain the entirety of the shortfall in MMR vaccine coverage in a number of states. For example, Alabama and Indiana have relatively low MMR vaccine coverage rates, which fall below the herd immunity threshold (in the 89.7%-92.4% range), but relatively low rates of vaccine exemptions (in the 0.1%-1.7% range). This suggests that vaccination coverage shortfalls are not just arising due to vaccine exemptions but could also be due to other factors such as inertia and/ or a lack of knowledge. Most states could reach herd immunity for measles if children without vaccine exemptions were actually vaccinated. Learn more about recent reseach on this issue.
Several states are considering new laws to curb vaccine exemptions for measles.
California already abolished non-medical measles vaccine exemptions and is now well on its way to herd immunity.
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