By late March it seemed that covid was winding down here in the US. Infection rates and deaths were in rapid decline, while 3 million people were getting vaccinated every day. Herd immunity seemed imminent — only a couple of months away. IHME projected that daily infections would drop to around 14K by the end of May. Then the trends reversed course: vaccination rates decreased dramatically, even as the much more contagious delta variant spread through the population. This past week, estimated infection rates have equaled or exceeded peak pandemic levels from late 2020.
Now it turns out that vaccine immunity wanes over time. That’s not a total surprise: flu shots also lose much of their protective power after six months. What’s disappointing is that the US didn’t reach herd immunity two months ago, eradicating community contagion before vaccine effectiveness began to fade.
As a consequence the public narrative has changed: covid will likely be with us permanently. In the relatively short run covid will surge annually and seasonally like the influenza virus, necessitating annual boosters to reinforce our fading immunity while protecting us from new variants. Eventually covid will become more benign but more endemic, like the common cold: no more vaccines, just the occasional bout of relatively mild illness.
I’m not sure this new narrative makes sense.
Every flu season the virus eventually peters out due to herd immunity, achieved through a combination of vaccines and infections among the population, so by the time the vaccine’s effectiveness begins to degrade community spread of the flu has ended for the season. Between seasons the influenza virus mutates rapidly and radically in other parts of the world, circumventing immunity achieved in earlier years and requiring a lot of scientific guesswork as to the molecular structures of the newly evolving variants that will show up on our shores.
That’s not how the covid virus works. First, while covid infection rates ebb and flow, they’re not reliably seasonal. Second, the now-dominant covid delta variant is far more contagious than the typical flu bug, so a much higher proportion of the population will need to acquire immunity in order for any new covid surges to extinguish themselves. On the other hand, the covid vaccines are far more effective than flu vaccines, so with adequate vaccination rates covid contagion could be suppressed even more effectively than the flu. And the covid virus mutates much more slowly and much less radically than does the influenza virus, so it should be easier to roll out predictably effective booster shots.
I realize I’m veering pretty far out of my lane here, but here’s what seems likely to unfold on the go-forward:
- Around 55% of Americans have been vaccinated, conveying an estimated 85% immunity, while maybe 40% of the unvaccinated have already been infected. So that’s (.55 x .85) + (.45 x (1 – .40)) = 74 percent immunity within the US population. That leaves 26% of 330 million = 86 million Americans still exposed to covid.
- Every day around 800K Americans are getting either their first or second shot, while 500K are getting newly infected. At this rate the US will approach 100% covid immunity by the end of November. New infections should dwindle to very small numbers by then.
- Meanwhile, immunity provided by the vaccines will gradually begin to degrade. Starting in September, boosters will be made available to everyone in the US, beginning with those most vulnerable to severe illness and those most exposed to community contagion. These boosters are very effective against delta, restoring protection to very high levels.
In short, it seems likely that the current big surge in covid infections might be the last one we face in this country. If rollout of the boosters is as widespread as the ongoing first wave of vaccination, then future new covid surges will be small, brief, and much less lethal than seasonal flu outbreaks. Population immunity against existing and new variants evolving in the world will be maintained by regularly scheduled booster shots administered every 8 months or so.
What could possibly go wrong? Haha, that’s a good one.
- Adult vaccine holdouts. It’s likely that in the foreseeable future a sizeable proportion of the US population will never get vaccinated. Given the delta variant’s high rate of contagion, pretty much all of the unvaccinated will get infected sooner or later. Preliminary evidence indicates that immunity acquired via infection lasts longer, and is more robustly adaptible to new variants, than is immunity acquired via vaccination. If so, then the effective rate of contagion will be slowed significantly during future covid surges.
- No child vaccinations. Since the vaccines aren’t yet approved for use in children, and since the delta is so contagious, most kids will likely have been infected by covid by the end of this year. The vast majority of infected children are asymptomatic; practically none experience severe symptoms. As with the unvaccinated adults, the children will likely retain their immunity for quite some time. In fact, it might even be good policy not to immunize preteens, letting them build up natural immunity over successive rounds of infection, effectively rendering the covid virus as relatively harmless as the viruses that cause the common cold.
- Vaccine-resistant variants. There’s preliminary evidence that the lambda variant is more effective than delta at evading both vaccines and natural immune defenses. Lambda has been in the US for a while now, but it seems to be much less contagious than delta so it hasn’t gained much of a foothold. Will widespread immunity against delta open up an opportunity for the lambda strain to achieve dominance? If so, the rate of severe illness and fatality is likely increase markedly among those who get infected, as has been the case in Peru where lambda is widespread. As the virus adapts, can the virologists and pharmacology scientists and bioengineers adapt? The original covid was a new organism when pharmacologists developed the first wave of vaccines, which they accomplished at unprecedented speed. Is it hubristic to expect R&D to achieve similarly effective protections against new mutations as they arise?
- Unknown unknowns.