January 2022 is one of the worst possible times to get Covid-19. That’s not only because hospitals are dangerously full, but because after nearly two years of gradually learning more about SARS-CoV-2, the omicron variant has thrust scientists and doctors back into a state of ignorance and guessing. Tests and treatments are in short supply. But this isn’t March 2020 all over again; in fact, the situation is likely to improve dramatically in just a couple of months.
Omicron seemed to come out of left field. Scientists had predicted that any new variants would likely be offshoots of delta, since that variant accounted for most infections worldwide, but omicron is a distant cousin that nobody knew existed until it was rising at an alarming rate in South Africa.
Scientists are still trying to figure out if delta’s decline is being caused by omicron’s rise, or whether omicron is just making it look small by comparison. And more broadly, they’d like to know how new variants take over, since this is a phenomenon that might happen again.
“It is somewhat mysterious why we see these surges appear and you have one variant completely replace the other,” said Jeremy Luban, an infectious disease specialist at University of Massachusetts Medical School. “We saw that with Alpha when it first appeared, it was quite startling.”
There is evidence that immunity is allowing omicron to actively push back its predecessor. Recent unpublished data from a respected group in South Africa demonstrates that omicron infection leaves people with immunity that defends against delta. The cross immunity between the variants works much better in this direction. People infected with delta appear to have very poor protection against omicron.
That asymmetrical immunity would clearly give omicron an advantage, but it’s still not clear whether delta could hide somewhere and return, maybe in an altered form that evaded omicron antibodies.
Luban said that omicron infections may also be preventing the delta variant from spreading to new hosts. “Viruses, once they enter cells, can actively block entry from other viruses,” he said. They don’t like to share hosts. Omicron appears to be much more transmissible, so it’s winning this footrace.
These fundamental questions have big practical implications. For example, monoclonal antibody drugs that saved lives and truncated illness earlier in the pandemic are no longer being offered in most places because they don’t work against omicron, which responds to a different drug. And few hospitals have the resources to analyze each patient to figure out whether they have omicron or delta, which still isn’t completely extinguished.
Then there’s the question of why and how omicron spreads so much more readily than other variants. It doesn’t appear to leave people with a higher “viral load,” but it might linger at levels that keep people infectious for longer, said Mark Siedner, an infectious disease epidemiologist and clinician at Massachusetts General Hospital.
That’s a touchy subject now that the CDC has shortened its recommendations for isolation and quarantine, and questions are arising about the ability of rapid tests to catch cases early enough to stop transmission.
Siedner is involved in a study aimed at measuring how long people remain contagious with omicron infections. PCR tests are notorious for coming up positive for days or weeks after people have cleared any live virus, because the test can find inert remnants of viral RNA. So his group will test people who’ve come up positive every couple of days for several weeks to see if they can isolate samples of the virus that are still viable.
That data could help CDC formulate better guidance on isolation and quarantine. “I’m hoping in the next week or two we’re going to be able to show fairly clearly how long are people contagious with omicron,” he said. “I know the CDC is asking us to isolate for five days ... If people are infectious for 10-15 days … that might explain some of what we’re seeing.”
So scientists won’t remain in the dark about omicron forever — or even for very much longer. And after this winter surge is over, it will be easier for everyone to get tested and easier for the sickest to get the right monoclonal antibodies. In just a couple more months, doctors expect to have antiviral pills that work against all known variants.
Some experts have warned that nearly everyone will get this virus in one form or another eventually, and that may be true if it hangs around for decades. But timing is everything.
Bloomberg
