For many months, members of the public have equated a return to “normal life” with the phrase “herd immunity”: that threshold reached when the Covid-19 pandemic would be boxed in by immunization campaigns, find no new hosts and society would return to a 2019-style normal.
However, many scientists and experts have also warned for months that the US will not reach this threshold this year, or perhaps even next. That is because of a number of important factors including high levels of vaccine hesitancy in the US, and a still globally widespread Covid-19, which is leading to new variants.
Warnings about the inability to reach herd immunity have been especially pronounced since a major slowdown in US daily vaccinations. This is what we know about what normal could look like if we don’t reach herd immunity before next fall and why we will live with the virus.
Why won’t we reach herd immunity?
Herd immunity rates change based on how contagious a given virus is, the efficacy of available vaccines, the number of people who receive the vaccine, and the propensity of the virus to evolve, among other factors. Measles is a good example.
Measles is one of the most contagious viruses known to humans, but also has a very safe and effective vaccine, which prevents 93% of cases. The infectiousness of measles means a very high proportion of the population needs to be vaccinated to prevent breakout infections – about 95%, according to the World Health Organization.
More than 90% of the US population is inoculated against measles, a high vaccination rate. But this still is not enough to prevent localized outbreaks in social groups with much lower vaccination rates. These outbreaks can then spill over into the larger community.
The virus that causes Covid-19, Sars-CoV-2, is subject to the same pressures as measles, but has distinct advantages. First, worldwide circulation of Covid-19 gives the virus millions of opportunities to mutate, evolve and evade vaccine conferred immunity. High vaccination rates have prevented this phenomenon in measles.
That is why experts often refer to the immunization campaign as a “race between vaccines and variants” – vaccines must be distributed quickly to tamp down on variants. Otherwise a vaccine becomes a static solution to a moving target.
Further, the coronavirus is still “novel”. Unlike measles, scientists are uncertain how long Covid immunity lasts, though for natural immunity it could be as short as a few months. Many experts believe people will need either boosters or variant-specific vaccines in the future.
Even before more contagious “escape variants” were identified, such as the B117 variant first discovered in the UK, the US was going to have a very difficult time reaching herd immunity because there is no vaccine available for roughly 20% of the population – children.
High levels of vaccine hesitancy and continued inequities in how the vaccines are distributed could also contribute to localized outbreaks in areas where inoculation rates are lower.
“One of the big concerns is that the result will be pockets of communities that are well protected, and pockets that are vulnerable,” Samuel Scarpino, a researcher studying infectious disease dynamics at Northeastern University, told the Guardian in March.
Conservative states appear especially vulnerable
Conservative states have proved especially hesitant to get vaccinated. Among adults, 20% told surveyors with the Kaiser Family Foundation they will either “definitely not” (13%) get the vaccine or only do so “if required” (7%). Another 17% say they will “wait and see” whether to get the vaccine. Republicans are the most vaccine hesitant group.
Nearly one-third of people who identify as Republican (29%) said they would “definitely not” get vaccinated. Inequality will probably amplify the impacts of vaccine hesitancy. Some conservative regions with the highest rates of vaccine hesitancy also tend to have worse overall health, weaker public health infrastructure and higher overall levels of poverty and poor housing, which can make infectious disease spread worse.
“We have to help our conservative brothers and sisters,” Dr Peter Hotez, the dean of the National School of Tropical Medicine at Baylor College, recently told the Guardian. Otherwise, Covid-19 could become a “red state” disease.
What does that mean for the future of the pandemic?
The “new normal” is going to depend on where you live, and how local officials have decided to implement or ignore public health measures.
Oregon is limiting indoor dining in half the state after Covid-19 cases grew for five weeks straight, to 123 new cases per 100,000. But in Michigan, where the per capita case rate is 3.5 times that of Oregon, the governor is avoiding new restrictions in favor of advertising reopening once vaccinations reach a certain level.
In another recent example, Florida’s Republican governor, Ron DeSantis, just lifted all pandemic mitigation orders through executive order on Monday, and enacted a permanent law allowing state officials to overrule local health authorities at anytime. Florida is seeing 195 new Covid-19 cases per 100,000 residents.
All this means that even as the science of Covid-19 has not changed – social distancing, masking, testing, contact tracing and vaccination all limit new infections – how these measures are carried out has become distinctly local and political. Localized outbreaks will test leaders’ resolve and consumers’ patience as the US enters fall 2021.
As professor Ali Mokdad from the Institute for Health Metrics and Evaluation (IHME) at the University of Washington told the Guardian in February: “We’re not going to reach herd immunity, simply, we’re not going to reach it. It’s going to be seasonal, and it’s going to be like the flu, and we’re going to need to be ready for it.”