LET'S REMINISCE: Will herd immunity save us?
The idea of “herd immunity” against COVID-19 has achieved almost magical status in the popular imagination. When we reach that threshold, many Americans believe, we’ll be in the clear, and the pandemic will finally fade away.
First, let’s define “herd immunity.” It’s a form of protection from infectious disease that can occur with some diseases when a sufficient percentage of a population has become immune to an infection, whether through vaccination or previous infections. The exact herd immunity threshold varies depending on how contagious the disease is, but the best estimates for COVID19 are that 70-80% of the population would need to be immune.
By the most optimistic estimates, the combination of vaccinations and previous infections so far amounts to about 150 million Americans having some immunity, in a population of 330 million. That is under 50% of the population—very far from the 80% needed for herd immunity.
And the truth is that we are unlikely ever to reach herd immunity with COVID-19—it’s not how this nightmare will end. Although case counts are now declining from their winter peak, we expect another spike from potential super-spreader events following Memorial Day and the Fourth of July.
Moreover, such math misses a crucial point: The virus is changing so rapidly that immunity to the COVID strain of yesterday may not protect against today’s or tomorrow’s strain. We now face the challenge of new variants that may elude immunity created by natural infection and possibly by vaccines as well.
There is also the issue of vaccination rates. Many Americans cannot get vaccinated for medical reasons. Others have been left out of vaccination outreach or distrust the medical system. Children count as part of the “herd” but are just beginning to be vaccinated. Each year there will also be new births. But the biggest challenge is the 20-30 percent of Americans who say that they will either definitely not or probably not get vaccinated.
If herd immunity is out of reach, does that mean we’re doomed? Not at all. But we must supplement the impressive recent rollout of vaccines with a rapid-response system, modeled on the strategy that was used to fight smallpox in the early 1970s. Smallpox was eradicated from the globe in 1980—the first disease to meet this fate.
The key to the smallpox campaign was aggressive contact tracing: finding every case of smallpox, tracing it backward to sources of infection, tracing parallel chains of disease transmission, and tracing contacts forward to find those who would become at risk for infection. In the pre-internet days of the 1970s, this meant going house to house to inquire.
Today, time is of the essence in finding new COVID-19 variants. The disease travels at warp speed, whether it is moving between states, imported from other countries or spreading as new variants from animal populations. Finding the first cases within days, when an outbreak still amounts to just a handful of cases, is essential. When an outbreak goes undetected for weeks, it can generate hundreds or thousands of cases, and contact tracing and containment become much more difficult.
Nor is just finding new generic COVID-19 cases enough. We need to know what variant of the virus is involved. Enhanced testing will be critical and should include faster and cheaper tests and viral sequencing to aid vaccine and drug design. We will need to match new variants of COVID-19 with the vaccines most effective against them.
It is not too late to find, isolate and vaccinate those who do not yet have COVID-19 but are most likely to get it. It is not too late to use just-in-time vaccination to stop outbreaks in midcourse and prevent the spread of infection.
Jerry Lincecum is a retired Austin College professor who now teaches classes for older adults who want to write their life stories. He welcomes your reminiscences on any subject: firstname.lastname@example.org. The views and opinions expressed here are the author’s own and do not necessarily reflect those of the Herald Democrat.