Giving Compass' Take:

• Lavanya Vasudevan and Gavin Yamey explain the importance of having herd immunity reinforced by as many people as possible. 

• How can funders work to spread accurate information about vaccines and herd immunity? 

• Learn how to have productive conversations with vaccine skeptics

One common argument some parents make for declining vaccines for their children is that vaccines are not necessary—that their children are unlikely to get sick even if they are not vaccinated. Perversely, this argument relies in part on parents’ confidence that many other children are being vaccinated, creating “herd immunity” that makes it difficult for outbreaks to spread. In other words, if all my neighbors’ children get vaccines, my own unvaccinated children will benefit from the protection of the herd. But what happens if several neighbors also decline vaccines for their children?

Disturbingly, vaccine refusals are increasingly the reality in many parts of the US and elsewhere. In Europe, for instance, 90,000 cases of measles were reported in the first 6 months of 2019 alone. According to vaccination records of children entering kindergarten in the US last year, the number of parents seeking and receiving exemptions from required measles vaccinations increased to 2.5%, compared to 2.1% reported during the 2016-17 school year. As the US faces its worst measles outbreak in 20 years, these trends signal a dangerous lack of public understanding about how herd immunity works.

Typically, 93% to 95% of a population must be vaccinated to achieve herd immunity and prevent an outbreak of measles. Currently, the coverage rate in the US for the vaccine against measles in children 19–35 months is 90.4%, not even within that range. In 20 states, the vaccination rate is below 90%.

But even in states with rates above 93%, herd immunity offers no guarantees. The protective effect of herd immunity can vary based on the “herd” that an individual moves with. Relocation, travel or even a new circle of friends can change the composition of one’s herd, and thus its shared protection against infection.

Read the full article about herd immunity by Lavanya Vasudevan and Gavin Yamey at Global Health NOW.