Update on Herd Immunity

Biology/Immunity Infection and Spread Vaccines

Update: We know there is on-going chatter about herd immunity. We are re-posting the explainer below, as little has changed as far as the assumptions for what it would take to achieve “natural” herd immunity.

TL;DR: it’s bleak. Even at a theoretically lower threshold (50% vs 70%), the expected number of deaths is devastating.
So remember:

Dear Pandemic
June 28 ·
Q: Maybe this increase in cases is good…. aren’t we getting closer to herd immunity?

A: NO and NO!

It’s been a while since we touched on herd immunity, so first some quick review. If we think of SARS-CoV-2 infections as sparks, uninfected people are the fuel. The very basic idea of herd immunity is that individuals who are already immune–either through previous infection or a vaccine–act as a “firewall” that prevents continued spread of the virus. An infected “spark” has much less chance of reaching new fuel because of these firewalls of people who cannot get infected, and thus becomes much more likely to die out rather than spread.
Current estimates for the % of the population needed for SARS-CoV-2 herd immunity is around 70%.
So how much of the population has already been infected? Drumroll…estimates vary, but in the range of 3% in the US, 5% for the UK and Spain. “Hotspots” within these countries have reported higher levels of seroprevalence (evidence of previous infection): Possibly near 20% in NYC, 17% in London, and 11% in Madrid (though a caveat that the methodology of these studies varied).

The bottom line is that most people remain susceptible and doing some very back of the envelope math on the potential number of deaths associated with herd immunity in the US is *extremely* sobering.

If we use a generous estimate of 5% of the US population already exposed, and a lower bound estimate of current deaths (127,000), reaching 70% prevalence for herd immunity requires 14X more infections, corresponding to 1,778,000 deaths.

This is 1.78 MILLION deaths, more than the total number of U.S military deaths IN ALL WARS COMBINED.

Of course, these are very rough estimates/extrapolations, but you can see that even a number half this large is devastating.

On top of this, COVID-19 deaths are the tip of the iceberg regarding impact on health. Survivors who have been in ICU or on mechanical ventilation can suffer long term disability. We are learning more about potential long-term effects of COVID-19 infection among survivors, so a “goal” of 70% infection would mean over 200 million Americans potentially dealing with long term health effects of this infection.

We have no assurances that immunity due to previous COVID-19 infection is protective or long-lasting. While we hope based on other coronaviruses that immunity may last a year or two, even with widespread infection we are not necessarily keeping people out of the “susceptible” pool for long.

SO….while the idea of herd immunity to get the pandemic over with is appealing, to avoid death and suffering on a HUGE scale, we need to achieve this by vaccination rather than natural infection.

Or in other words, pursuing herd immunity for COVID-19 through infection is like BURNING YOUR HOUSE DOWN TO PUT OUT A KITCHEN FIRE.

Q: What if we don’t get a vaccine?

A: There is of course no guarantee that a vaccine will come, but the Nerdy Girls remain optimistic about the variety of vaccines in the pipeline and at various levels of clinical trials.
But even if we don’t get a vaccine, slowing down and containing the virus rather than letting it spread like wildfire also BUYS CRITICAL TIME for the development of better treatments and therapeutics, which could completely change the worst-case scenario if a large percentage of the population is ultimately infected.

Finally, while this pandemic is going to be a marathon not a sprint, several countries such as South Korea, China, and Australia have shown that suppression and containment IS possible.
So keep up the good fight– with testing and tracing we can stamp out the SARS-CoV-2 embers, and with physical distancing and masks we can deny SARS-CoV-2 the fuel it needs to grow.
Excellent explainer of herd immunity: