As we watch this once in a century pandemic unfold, experts have been keeping a close eye on the emergence of new variants of SARS-CoV-2. In fact, experts have long known that the true scope and harm of this pandemic will likely be determined by a race between getting enough people vaccinated to reach herd immunity and the emergence of new variants that are potentially more contagious and deadly. The worst case scenario would be the emergence of a variant that is largely immune to existing vaccines and can re-infect previously infected people, resetting the clock on the pandemic.
That worst case scenario has not happened yet. But the increasing emergence and rapid dominance of new variants is worrisome. The recent delta variant (technically known as the B.1.617.2 lineage) is the most worrisome of all. This variant was first detected in India in December 2020. By April 2021 it was the most common variant in India, and is largely the cause of their recent and deadly wave of infections. It has now spread to at least 80 countries, including the UK and the US. In fact it is likely the most common variant in the UK. As of May 22, it was 2.7% of cases in the US.
What makes the delta variant concerning is that it appears to be about 60% more infectious than the alpha variant (previously known as the UK variant), which itself is more infectious that the original variants of SARS-CoV-2. This means that the virus spreads more easily and more quickly, which is why it rapidly dominates any population it spreads to.
UK data also shows that those infected with the delta variant are more likely to be hospitalized with their illness, so it appears to cause a more serious infection. However, almost all of those admitted to the hospital with the delta variant have not been vaccinated. Two doses of the mRNA vaccines prevent hospitalization by about 90%.
The delta variant highlights exactly what experts warned about earlier in the pandemic. The more this virus has an opportunity to spread, the greater the probability that new variants will emerge. The more infectious a new variant, the more it will dominate new infections. And then eventually we get variants of variants, and mutations favorable to the virus begin to accumulate. The virus will progressively adapt to its human hosts.
We can also see the effectiveness of the currently available vaccines. They prevent spread of the illness, and reduce severity of infections. This in turn reduces hospitalizations and the need for resources to treat seriously ill patients. India’s recent experience is an example of what happens when resources are overwhelmed – when you run out of oxygen, the death rate spikes.
The good news is that our vaccines still work against the spread of the current batch of variants. But we are not at herd immunity yet. The delta variant is spreading in the US and Canada in pockets of populations that are unvaccinated. This could not make the situation more clear – those who refuse to get vaccinated are putting everyone else at risk by allowing the virus to spread, maintaining the pandemic, and allowing for new variants to emerge and spread.
This leads to a now common question – when and if we will need a booster vaccine to maintain protection and to cover new variants. So far, it seems the vaccines are maintaining immunity, and they are covering known variants. We can only make an educated guess about when boosters will become necessary, and hopefully the vaccine will hold for at least a year. However, we may need boosters before that to extend coverage to new variants. Moderna is already working on newer versions of the vaccine specific to the new variants.
Where will all this end up? There are several possible outcomes. The worst outcome would be something like the 1918 flu pandemic, that eventually burned itself out but only after killing 50 million or more people worldwide (the COVID-19 death toll is approaching 4 million). That is not the path we want to take to herd immunity. The best outcome is that we will get enough people vaccinated, while maintaining sufficient measures like social distancing to reduce spread, and achieve herd immunity without any significant further waves. This would likely take a greater effort than the world is currently doing.
The third, and perhaps most likely, outcome is that COVID-19 becomes endemic (like the flu). The infection never fully burns itself out, but it is sufficiently reduced that we are no longer in a pandemic. Rather, the infection simmers along causing occasional epidemics, mostly in unvaccinated populations. It seems likely that we will be getting our annual COVID vaccine alongside our annual flu vaccine, and organizations like the CDC will have to track annual infections and deaths every year like they track the flu.
Unfortunately, it seems like we missed our window to prevent COVID from becoming endemic, but we may still luck out. Leaving it to luck, however, is not a good plan. Now is the time to vaccinate the world against this disease, because a pocket of infection in a distant country can breed a new variant that will ultimately spread around the world. We may still win this race, but the emergence of the delta variant makes it seem more likely that we may have to settle for a tie.