People who refuse vaccinations for contagious illnesses rarely suffer consequences for their decisions because herd immunity protects them.

Herd immunity is the resistance to the spread of a contagious disease within a population that results from a sufficiently high proportion of individuals being immune to the disease. Such immunity can be the result of either natural infection or vaccination. Counter to what’s out in the media, herd immunity is unlikely to protect us from COVID-19. Our ticket back to normal is getting vaccinated.

There isn’t any evidence that natural infection with SARS-CoV-2 leads to the long-term protection necessary to generate herd immunity. To the contrary, the four seasonal coronaviruses that cause upper respiratory infections circulate every winter and spring. We’ve all had them, probably more than once. Protective immunity only lasts two or three years, and then we can catch them again. What this means is that if SARS-CoV-2 follows suit, without vaccination, most everyone will eventually catch COVID-19.

Will the COVID-19 vaccines be able to generate herd immunity? It’s too early to tell. It may be that the COVID-19 vaccines will act less like the measles vaccine and more like the flu vaccine.

Measles vaccines induce sterilizing immunity. That is, the measles vaccine entirely stops infection and therefore prevents transmission. On the other hand, current flu vaccines are only so-so at preventing infection. Some vaccinated individuals still catch the flu and can transmit it.

Even though the flu vaccine isn’t bulletproof against infection, the good news is that vaccinated individuals who become ill are less likely to become seriously sick than those who are unvaccinated. We don’t see much of a herd effect with our flu vaccines.

A case could be made that the flu vaccine doesn’t generate herd immunity because only about half of the population is vaccinated each year. Estimates are that in the case of COVID-19, 70 percent of the population will have to be vaccinated to generate herd immunity. That’s an incredibly high bar to meet.

First, children make up a quarter of the population, and they will not receive the vaccine anytime in the near future. Before vaccine testing can even begin in children, it will have to be shown safe and effective in adults. As a result, most adults will need to be vaccinated, which is doubtful when vaccination is a personal choice. Many adults believe that they’re not at risk of SARS-CoV-2 and will pass on vaccination. The vaccine will not be mandated by law.

Sadly, politics have crept into vaccine development and those who shun vaccines continue to try to frighten others from the COVID-19 vaccines. None of this is surprising. Just look at recent battles over the safe and effective measles vaccine that has been saving lives for over half a century.

Without herd immunity, vaccination against COVID-19 vaccine will be necessary. When you make your choice, keep in mind the real risks of COVID-19.

Vaccine Smarts is written by Sealy Institute for Vaccine Sciences faculty members Drs. Megan Berman, an associate professor of internal medicine, and Richard Rupp, a professor of pediatrics at the University of Texas Medical Branch. For questions about vaccines, email vaccine.smarts@utmb.edu.

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