Do Vaccines Prevent COVID-19, or just Delay It?
First, the good news: it looks like global Reff for SARS-CoV-2 is approaching 1. However, what lies next? Do we see sharp case declines like India and Indonesia did after Delta passed, will we see a lingering high level of cases like South Africa, or something else entirely?
Second, the bad news: it's unlikely to stay at or below 1 for long. That could always have been anticipated due to the high R0 and evolutionary rates of SARS-CoV-2.
Unlike India and Indonesia, heavily vaccinated countries like the UK are demonstrating protracted Delta waves, which raises independent questions about whether vaccination prevents cases or just delays them.
The US is as well. Still, Reff is trending towards 1 here, albeit at a very high level of cases. We can expect it to hover there as it moves north with the changing seasons.
A brand new letter to the editor in the NEJM depicts this perfectly. You will see that infection happened more frequently in unvaccinated health care workers in early months, but now vaccinated workers are being infected more frequently than unvaccinated workers, and "symptoms were present in 109 of the 130 fully vaccinated workers (83.8%) and in 80 of the 90 unvaccinated workers (88.9%)." 75% of new infections are in vaccinated workers, a number that slightly underestimates the vaccines' efficacy since slightly more workers were getting vaccinated over time, but not much, and it will make the vaccines look more durable than they are.
https://www.nejm.org/doi/full/10.1056/NEJMc2112981It looks like vaccines are effective for about 6-7 months at this point, and that duration should shorten. Each exposure to the virus is a new roll of the dice, and while lowering each roll's odds of success happened through the initial gradual mass vaccination campaigns, it also promoted the viability of immunoevasive strains. This means that after we get a high enough percentage of the population vaccinated, the odds of success of each roll should start to increase again through viral mutation. Antigenic drift will help in this process and thus be actively selected for. As mentioned in my last post, we need to look at areas under the curve, and there isn't enough data yet.
Every successive dominant strain of SARS-CoV-2 has been more deadly with the exception of D614G: Alpha is more dangerous than the originals, and Delta is more dangerous than Alpha. While there is room for hope that future strains will be less severe, empirical evidence thus far is to the contrary. Different viruses have ended up at wildly different levels of severity and maintained those levels for a long time. Vector-borne viruses can become almost totally lethal, because they depend on the survival of their vector, not their host. We do not know the equilibrium level of virulence for SARS-CoV-2, but it's likely higher than Delta showed in unvaccinated people, and vaccination will likely make it hyper-virulent in unvaccinated people for awhile, because the vaccinated are effectively serving as vectors.
SARS-CoV-2 vaccines will protect for progressively shorter periods of time until too many serotypes arise, or ADE and OAS become powerful enough to make vaccination actively dangerous. We should also remember that some of the worse outcomes from SARS-CoV-2 come from long COVID, and that can arise from an infection of any severity. The QALY of people worldwide can be expected to drop.
As another piece of good news, there isn't an obvious candidate strain to pick up the slack immediately. There are several strains that have a good chance(I favor C.1.2 or B.1.621), but it will take them longer because their Reff seems lower than that of Delta's when it broke out, so we may get a reprieve this winter. Multiple strains could succeed in parallel, but they're not likely to reach high case counts quickly simply because of low starting points, less amazing transmission than Delta, and they have to deal with a lot more existing antisera.
However, there are plenty of candidate strains to take over after some time has passed. Most of them already exist, and a new one could pop out at any time, especially with recombination.
Please stay masked, vigilant, and use your own non-pharmaceutical interventions if you can -- like staying at home.
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