Now the U.S. is dealing with a new X-factor. Actually, it’s an XBB-factor: the XBB.1.5 Omicron subvariant. The XBB.1.5 comprised an estimated 40.5% of all Covid-19 cases over this past week, based on data from the Centers for Disease Control and Prevention (CDC). That’s up from 21.7% the week prior. That one week jump has vaulted the XBB.1.5 ahead of the BQ.1 and the BQ.1.1 subvariant as the new dominant subvariant in the U.S.

This prompted a “Wow” on Twitter from Eric Topol, MD, founder and director of the Scripps Research Translational Institute, which I guess would qualify as a “Twow”

As another tweet from Topol indicated, this new XBB.1.5 was first detected in, guess where, the U.S.A.:

And what can happen when the SARS-CoV-2 is allowed to spread in unfettered manner? It spread, multiplies, mutates, and spreads. The more the virus spread, the more likely new subvariants will emerge. Asking the XBB.1.5, “Who’s your daddy,” could get a response like “The Omicron XBB subvariant.” That’s if the virus had a mouth. The XBB.1.5 emerged via mutations to the XBB variant. The XBB variant has already spread to over 70 countries, such as India and Singapore. The XBB, in turn, likely resulted from a hook-up between two other earlier Omicron subvariants, the BA.2.10.1 and BA.2.75. And that kids is what happens when you allow the virus to just keep spreading.

The rapid rise of the XBB.1.5 demonstrates that this version of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) may have a “growth advantage” over the other versions of the virus. While a “growth advantage” may sound great in bed, that’s not the case when you are talking about a new version of a respiratory virus. It suggests that the XBB.1.5 could be more transmissible than previous versions of the SARS-CoV-2. Or it could be better at getting past existing immune protection. Or both.

As a result, there could very well be yet another a post-Holiday season Covid-19 surge, this time driven by the XBB.1.5. During these past two weeks, many people seem to have shunned Covid-19 precautions as if they were quilted puffer vests or low shaft booties, in other words, out of style. That’s not great when many folks are traveling and attending gatherings. It makes you wonder whether the ball dropping on New Year’s Eve will have spikes and be a Covid-19 coronavirus.

Each time a new variant and subvariant of the SARS-CoV-2 has become dominant, five natural questions have emerged. One is whether people infected with this new version will be more contagious than they were with previous versions? Two is will this new version make people sicker than previous versions did? Three is will this new version be able to get past vaccine-induced and natural immune protection? Four is whether treatments will be as effective against this new version? And five is what the bleep?

The answer to the first question is maybe. Or alternatively, perhaps.

The answer to the second question is “Doesn’t seem that way,” so far. There doesn’t seem to be differences in the percentages of people who get very severe Covid-19 after getting infected with the XBB.1.5 versus other previous Omicron subvariants. Sure, Covid-19-related hospitalizations have been going up in most parts of the country. According to the New York Times, the average number of daily Covid-19-related hospitalizations has bumped by 4% up to 42,324 over the past two weeks. However, hospitalization rates in parts of the country where the XBB.1.5 has already become dominant haven’t necessarily been higher than where other subvariants are still more dominant.

The answer to the third question is “looks that way.” Given the F486P mutation that the XBB.1.5 has, the big concern is how much more evasive the XBB.1.5 may be. In this case, evasive doesn’t mean that the virus refuses to answer when you ask, “Where were you last night?” Rather, the XBB.1.5 may be more able to evade antibodies generated by Covid-19 vaccination or prior Covid-19 infections. This could mean that the XBB.1.5 may be better able to get past your immune defenses.

This new evasiveness would help provide the answer to the fourth question too. That’s if there were any monoclonal antibody treatments available that still work against the circulating strains. This extended set of Omicron waves have essentially rendered ineffective all of those monoclonal antibody treatments that were effective against much earlier versions of the virus. Antivirals such Paxlovid and Remdesivir do still seem to work if taken early enough. However, this doesn’t leave clinicians a whole lot of specific treatments until more monoclonal antibody treatments can be developed.

So what can you do to stay safe from the XBB.1.5. Well, there is the same-as-it-ever-was layering of precautions such as high quality face masks, ventilation, air filtration, testing, and vaccination. If you haven’t gotten the bivalent Covid-19 booster yet, it’s a good idea to do so as soon as possible. A research letter publised on December 21 in the New England Journal of Medicine described a study that found how the Moderna and Pfizer-BioNTech bivalent Covid-19 mRNA boosters generated a significantly better antibody response against the XBB variant than the original Moderna and Pfizer-BioNTech Covid-19 mRNA vaccines. The study didn’t look specifically at antibody activity against the XBB.1.5 but these results did suggest that the bivalent will give you better protection against the XBB.1.5 than the original versions of the vaccines.

In what’s become unofficially the complacency phase of the Covid-19 pandemic, it may be easy to forget that the SARS-CoV-2 is still a serious threat. The virus keeps multiplying, spreading, and mutating. And it can be difficult to keep of with these new subvariants that have names that sound like Wifi passwords. Eric Feigl-Ding, PhD, an epidemiologist and Chief of the COVID Risk Task Force at the New England Complex Systems Institute, wondered why the CDC didn’t alert the public to the spread of the XBB.1.5 earlier in the following tweet

XBB.1.5. is increasing in UK as reported by Prof. Christina Pagel in this tweet

Ultimately, the big X-factor over the coming months is how many people will end up getting the bivalent Covid-19 booster and maintaining Covid-19 precautions. If the answer is not too many, the XBB.1.5 may mark the spot with even more hospitalizations, deaths, and other bad Covid-19 outcomes. Politicians and various TV, radio, and podcasting personalities can claim that the Covid-19 pandemic is over. But that only gives this new subvariant X-tra opportunities to spread.