SARS-CoV-2 Update from David Wessner, PhD
As a friend recently said to me, “Looks like this dadgum virus is not done with us.” Unfortunately, truer words have never been spoken. So, as we enter the third summer of the COVID-19 pandemic, let’s take stock of where we are and consider what SARS-CoV-2 may have planned for us next.
The virus continues to spread.
According to data compiled by The New York Times, reports of SARS-CoV-2 infections nationally have been increasing since late March. Currently, around 100,000 new infections per day are being reported. This number is well below the daily averages seen during the initial Omicron wave, but significantly above the daily numbers being reported just two months ago. It’s worth noting that interpreting these numbers can be a bit tricky. The data represent cases reported to local or state health agencies. With the increase in at-home testing, many positive cases probably are not being reported. Thus, the actual number of cases may far exceed the reported count. The number of hospitalizations, in contrast, may present a more consistent metric. Nationally, this number also has been increasing over the past one to two months, but still remains far below the peak numbers seen earlier this year. In North Carolina, the percentage of all ER visits linked to COVID-like symptoms has increased, too. Today, about 5% of all ER visits in the state result from COVID-like symptoms. In April, the percentage was only 2%. In contrast, over a quarter of all visits to emergency rooms were linked to COVID-like symptoms in January of this year.
The virus continues to evolve.
Throughout the pandemic, we’ve heard about a seemingly unending array of SARS-CoV-2 variants. As I’ve written before, the appearance of these variants is not surprising. Viruses mutate. And mutants that have a selective advantage will prevail. The Alpha variant supplanted the original form of SARS-CoV-2. Delta then supplanted it. Now, Omicron reigns supreme. In each case, the newer variant has proven to be more transmissible than its predecessors. It spreads more easily from one person to another. Not surprisingly, a more transmissible variant becomes more prevalent. Although evidence pretty clearly indicates that successive variants of SARS-CoV-2 are more transmissible, data on the severity of these variants is less clear. Some studies indicate that Omicron infections in mice are less severe than infections with Delta. As the authors explain in this New England Journal of Medicine article, however, measuring the intrinsic severity of a variant in humans is difficult.
Multiple sub-variants of Omicron now are circulating.
Although the variant most common throughout the world right now still is classified as Omicron, sub-variants of it have emerged and are co-circulating. Earlier this year, a sub-variant of Omicron known as BA.2 prevailed in the United States. It recently was supplanted by BA.2.12.1. Today, about 60% of infections in the U.S. are caused by BA.2.12.1 and 34% are caused by BA.2. The other 6% of new infections are caused primarily by the sub-variants BA.4 and BA.5. These two forms of the virus are driving a new wave of COVID-19 infections in South Africa and, it’s worth noting, have increased significantly in prevalence in the U.S. in recent weeks.
Omicron sub-variants partially evade immunity.
The Omicron variants contain a large number of mutations, particularly in the spike protein, not seen in previous forms of SARS-CoV-2. As a result, researchers have been particularly interested in our immune response to this variant and the effectiveness of the existing vaccines against it. Two recent studies have addressed this issue in somewhat different ways.
In a study just published in the journal Nature, researchers asked whether infection with Omicron could provide people with immunity to other variants. First, the bad news. In both a mouse model and unvaccinated individuals, infection with Omicron produces a relatively weak immune response. Moreover, that response is fairly specific to Omicron. Sera from experimentally inoculated mice and unvaccinated people infected with Omicron displayed a limited ability to neutralize other variants. In other words, an infection with Omicron probably won’t provide protection against other variants. Now, the good news. Omicron breakthrough infections in vaccinated people seem to augment the immune response to other variants in those people. Based on this result, the authors speculate that a future vaccine might be most effective if it is heterologous and includes components of Omicron and other variants.
In another study, recently posted on the pre-print server bioRxiv.org, researchers approached this issue in a different way. Rather than investigate whether an immune response targeting Omicron could inhibit other variants, these researchers asked if immune responses targeting other variants could inhibit Omicron. Their data show that BA.2.12.1 and BA.4 exhibit increased resistance to antibodies produced by vaccinated people and vaccinated people who also had been infected by another variant. Bottom line from this study? Breakthrough infections among vaccinated people and re-infections of people who previously had been infected probably will be common with these sub-variants.
I’m currently in isolation. I’ve done all the right things over the past two and a half years. Worn a mask. Avoided indoor gatherings. Got vaccinated and boosted (twice!). Still, I felt sick a few days ago and tested positive. Most likely, I was infected by one of the Omicron sub-variants. Although I certainly am sick, I’m not severely ill. Even though the current vaccines are less effective against Omicron than the earlier variants, they still significantly reduce the severity of disease. Staying up-to-date on vaccinations and boosters remains our best approach to protecting ourselves and our community.
Yes, my friend, this dadgum virus is not done with us.
David Wessner is a professor of biology at Davidson College, where he teaches classes on microbiology and HIV/AIDS. Before joining the faculty at Davidson, he researched coronavirus pathogenesis at the Navy Medical Center. He has co-authored an undergraduate microbiology textbook and The Cartoon Guide to Biology.