GAO: A Herd Immunity For COVID-19 Primer

#15,354

`Herd Immunity' is widely touted - preferably via widespread vaccination, or less happily, acquired following natural infection - as our way out of the COVID-19 pandemic nightmare.  Once that is achieved, infections would be rare, and life can supposedly return to `normal'. 

While in theory, it should work, for us to get there without horrendous losses will require an awful lot of things to go right. And still it will likely take years . . . not months. 

Two days ago, in The Lancet: Prevalence of SARS-CoV-2 in Spain (ENE-COVID), we learned that Europe's hardest hit country has only seen about 5% of their population infected.  Estimates in the United States similarly run between 5% and 6%. 

While it's been said that `herd immunity' might be achieved once as few as 60% of the population have been infected or vaccinated, that - at least compared to other viruses - is a very optimistic projection.  Herd immunity for measles is over 90%, and for Rubella, Smallpox, and Polio it's well over 80%. 

And that assumes that infection (or vaccination conveys) long-lasting immunity, which has not been demonstrated with COVID-19 yet. 

Other coronaviruses, including MERS-CoV, SARS, and human coronaviruses (hCoV), have shown relatively short-term immunity following natural infection, particularly among those with mild or moderate illness (see COVID-19: From here To Immunity (Take Two)).

As far as the degree of protection offered by vaccine, we'll know when and if a SARS-CoV-2 vaccine is developed.  While many companies are working on one, previous attempts to create a SARS or MERS vaccine have failed to produce a commercially available vaccine. 

 
Hopefully, given enough time, money, and resources, a safe and effective vaccine can be developed.  Whether that is in 6 months, or six years, is anyone's guess.  But assuming eventual success, the bigger task will be in deploying the vaccine.  

Will it take one dose, or two?  How far apart?   Will it require yearly (or occasional) booster shots?  How much public resistance will there be to any new, fast-tracked vaccine?  

Vaccine production, even for seasonal influenza, can sometimes hit snags. Last year many countries did not receive their supply of flu shots until November or December (see NHS Update: More Global Flu Vaccine Delays).

During the 2009 pandemic, there were estimates that nearly 5 billion doses of the H1N1 vaccine could be produced in the first 12 months (see Recommendations of the Strategic Advisory Group of Experts (SAGE) on Influenza A (H1N1) vaccines.)

In the end those manufacturing goals fell short by 75% (see 2010's ECDC: Global Vaccine Goals And Realities), as the yield from the seed virus proved less than anticipated and the use of adjuvants – to reduce the amount of antigen needed per shot – was met with public resistance.

A little over a year ago, Japanese vaccine manufacturer Daiichi Sankyo formally apologized after 8 years of trying and failing to gear up to produce 40 million doses of an H5N1 pandemic vaccine in 6 months (see Manufacturing Pandemic Flu Vaccines: Easier Said Than Done).

How long it would take to produce, and distribute, hundreds of millions (or several billion) COVID-19 vaccinations is unknown.  But past experience suggests it won't happen quickly, or go smoothly. 

And how protective will it be? Particularly in the highest risk populations?

While we can always hope for a 100% effective vaccine across all recipients, that's highly unlikely. Influenza vaccines are roughly 50% protective, but often less for those over 65. But even if we assume a 75% effective vaccine, and one protects for a year or two, that may not be enough to produce herd immunity. 

If 75% of any population were to take a 75% effective vaccine, you'd end up with just 56% immunity (plus any naturally acquired immunity). And that may not be enough to dampen community spread.  

These are all issues we've covered before, and while governments like to project confidence and reassure the public (and the financial markets), they understand full well how difficult the road ahead really is.  

They just don't like to talk openly about it. 

Except for the GAO (Government Accountability Office), whose job it is to bring a measure of reality to the political table.  This week they've issued a Science, Technology Assessment, and Analytics report on the topic of `Herd Immunity' for COVID-19. 

Refreshingly devoid of the `happy talk' that normally flows from official sources, the GAO recounts just how much we don't know at this point about COVID-19 immunity, vaccine production and efficacy, and the prospects for achieving herd immunity in the near term. 

 

Follow the link to read the full report:

SCIENCE & TECH SPOTLIGHT: Herd Immunity For COVID-19

GAO-20-646SP: Published: Jul 7, 2020. Publicly Released: Jul 7, 2020.

HIGHLIGHTSVIEW REPORT (PDF, 2 PAGES)

Why This Matters

Increasing the immunity of a population to an infectious disease like COVID-19 can slow the spread of infection and protect those most vulnerable. However, with limited information about important aspects of COVID-19, there are challenges to understanding the implications of herd immunity in the current pandemic.

The Science

What is it? A population can establish herd immunity to an infectious disease once a large enough portion of the population—typically 70 to 90 percent—develops immunity. Reaching this "herd immunity threshold" limits the likelihood that a non-immune person will be infected. In general, immunity develops through either infection (resulting in natural immunity) or vaccination (resulting in vaccine-induced immunity). Herd immunity helps protect people not immune to a disease by reducing their chances of interacting with an infected individual. This process slows or stops the spread of the disease.

How does it work? Once a community has established herd immunity, someone without immunity is less likely to be exposed to an infectious individual during an outbreak. For example, because there are more people with immunity in the population, there are fewer people susceptible to infection, and thus the number of potential transmissions is limited. Similarly, those who are immune will not be infected, and thus will not transmit the disease to others. Both of these situations help limit the size of the outbreak.

If an effective vaccine is available for a virus, achieving herd immunity can require a high rate of vaccination in the community. For diseases that spread more easily, more people must have vaccine-induced or natural immunity to achieve herd immunity. However, if a virus mutates quickly, the community's herd immunity may be relatively short-lived because the immunity from prior infection or vaccination may no longer be effective. Also, the disease can still circulate in segments of the population that are not immune, such as those with weakened immune systems who cannot effectively form immunity.

For diseases where no vaccination is available, it is possible to develop herd immunity through exposure to, and recovery from, the disease. However, if COVID-19 runs its natural course, this approach would entail the risk of severe disease or death. Given the risk associated with COVID-19 infections, achieving herd immunity without a vaccine could result in significant morbidity and mortality rates.

          (SNIP) 

Challenges

• Limited data on immunity. Currently, there are a number of unknown factors, such as whether a COVID-19 infection leads to immunity and how long immunity might last. It may be necessary for more time to pass to monitor individuals who have been infected and recovered and thus determine how long they show disease immunity. This information is needed to determine the herd immunity threshold.
• Implications of natural herd immunity. Relying on natural immunity from the disease progression of COVID-19 could allow a population to establish herd immunity. However, such an approach risks exposing people to a debilitating and potentially fatal disease.
• Testing limitations. If infection confers immunity, researchers need accurate data on the number of recovered individuals and other disease transmission parameters to determine if or when herd immunity is achieved. Accurate testing data are critical to understanding these parameters. However, there are still challenges associated with the use and availability of antibody tests, as well as with determining their accuracy.
• Lack of vaccine. A vaccine could help a population safely achieve herd immunity. However, developing a vaccine is a complicated process that  is costly, typically requires 10 to 15 years or more, and many candidates fail during the development process. Efforts are underway, however, to accelerate the process for COVID-19.
• Inconsistent immunity. Even if herd immunity is eventually achieved, outbreaks may still occur because immunity may not be uniform across the general population.

          (Continue . . . .)

 

As a `high risk' individual, I genuinely want to see a safe and effective vaccine sooner rather than later.  But I also know that the road to having that vaccine is long and hard, and there may be one or more bridges out out ahead. 

Hopefully scientists will find detours and workarounds, but success is far from assured. 

In the meantime, we have to find ways to live and work as safely as we can during this pandemic, and be prepared for what may become a very long haul.