Herd immunity is population–level protection against the spread of an infectious disease that is based on pre–existing immunity of a high proportion of individuals in that population, either from prior infection or vaccination. The idea of herd immunity also acknowledges the need to protect a small proportion of our population who cannot be vaccinated for medical reasons. The level at which this is achieved varies with a specific disease and its infectivity. For measles, a level of 95% is required to protect the remaining 5%. For COVID-19, suggestions of immunity levels of 70% might suffice but higher levels, perhaps greater than 90%, may be necessary.
As of March 29, 2021, more than 30 million Americans have tested positive to COVID-19, 52 million have been fully vaccinated, and 94 million have received at least one vaccine dose for a population proportion of greater than 28%. The current vaccination rate is approximately 2.7 million people a day (~0.8%) and expected to climb.
Among the three vaccines that have received emergency use authorization, the United States has access to sufficient doses in hand and on order to provide the whole population full protection more than twice over. The overwhelming current priority is to encourage all those who are able to accept the vaccine as soon as it is available to them. Public service announcements and messages promoting vaccination from political and health leadership of the U.S. government, former U.S. presidents, public health scientists and other notable public individuals are circulating extensively.
This is an urgent race against time. The consequences of not fully controlling this pandemic as soon as possible are significant and potentially devastating. The most serious of these is the possibility of a variant developing and taking hold that renders the current vaccines partially or fully ineffective. Already the U.S. has at least three variants circulating from the UK, South Africa and Brazil along with at least two from California. Fortunately, while each of these exhibits altered characteristics from the original virus that the vaccines target, all remain responsive to the Pfizer, Moderna and Johnson & Johnson vaccines.
If nothing else, delay in reaching herd immunity will extend the time during which we need to remain locked down, unable to visit with our loved ones, or prevented from reengaging in normal community activities. The ongoing economic, physical and psychological health consequences of this are immeasurable. Besides the obvious health risk, vaccine reluctance may have significant personal consequences as well. One may not be able to board a plane, may not be able to attend a conference, concert or sporting event, nor might they be able to book a room in a hotel if they cannot demonstrate receipt of a COVID-19 vaccine or having received an acceptable exemption.
While the crucial need now is to vaccinate as much of the population as possible, as noted above exemptions (waivers) must be granted for those individuals that are not vaccinated. All states grant exemptions for medical reasons. Additionally, 45 states grant exemptions for religious reasons, and 15 states allow philosophical exemptions. It is expected that the largest portion of the population will be vaccinated and many fewer will not, for whatever reason. Naturally this raises concern of creating two classes within society and consequently introduces a need to allow individuals to demonstrate proof of vaccination or exemption that ensures everyone’s basic freedoms are protected.
To date, hundreds of millions of vaccinations have been administered the world over, and millions more are urgently being delivered on a daily basis. Since the beginning of 2021, the vaccines have dramatically reduced transmissions, hospitalizations and deaths with few reported side effects. We must hope the virus does not win this race.