Today’s entry: I never really understood why we needed a typical 70% herd immunity threshold for a virus that really only affected 30% of the population that would have relevant co-morbidities. I can’t ever remember a National effort to reach herd immunity for flu strains, we only sought to protect the vulnerable and make risk manageable.
Bottom Line: This note follows my update yesterday indicating that close to 60% of Florida’s adults have now been vaccinated with at least a first dose of a COVID-19 and when they’re factored in with those who’ve had COVID-19 we’re potentially getting close to the 70% threshold among adults which is considered the starting point for herd immunity. As we’re getting close to these targets it’s a good time to discuss the reason why health experts near-universally agree herd immunity is important in putting COVID-19 behind us and what’s different in comparison to the flu virus.
There are at least four viruses that caused epidemics but have been near completely mitigated by herd immunity through vaccines. Measles, mumps, polio, and chickenpox. The reason vaccines and herd immunity reached through them, have proven so effective is due to the lack of mutation of the viruses. Science has been and continues to be highly effective at developing vaccines that are effective against viruses that are known. The difference, in comparison to the traditional flu virus you referenced, is how much mutation there is from one year to the next.
According to the CDC, the traditional flu virus is literally always mutating and as they point out, that’s why it’s possible for someone to contract the flu multiple times within a given season. At whatever point the flu virus mutates enough that one’s immunity, either from a vaccine or existing antibodies, is no longer effective, there’s no protection. The rapid mutation is the reason there’s a new annual flu vaccine developed and why its track record is spotty at best.
The CDC has tracked the flu vaccine's effectiveness with its current methodology (adjusting for demographics) since 2004. Here's the scorecard.
- Most effective: 60% (2010)
- Least effective: 10% (2004)
- Average effectiveness: 40%
That’s a good segue way to discuss the differences with COVID-19. With the Moderna and Pfizer vaccines having proved about 95% efficacy in preventing COVID-19 infections, they’re already 35% more effective than the most effective flu vaccine in recorded history. The vaccines have also proven to be effective against the variants as well. What this suggests is that COVID-19 mutates far less than the traditional flu virus and if we’re lucky (we won’t know until we get there), will be more like the other viruses we’ve mostly put behind us with vaccines and herd immunity.
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