• William Miller, MD

COVID Omicron BA.4 & BA.5.

Reports are flying around about the two newest subvariants of Omicron, namely BA.4 and BA.5. To begin with, we should be reminded that most viruses mutate over time and the changes being seen in the Omicron variant are nothing unusual. As a virus mutates, some of the new mutations will give an advantage over previous variants and with time that new variant will eventually become the dominant strain. So, when we hear about this happening in the UK and USA, this is not cause for alarm. Like with previous shifts in the SARS-2 virus, the virus that causes the disease COVID, there is initially a great deal of speculation as to what this may mean for the population and for public health. Much of that speculation is based on preliminary studies that may give contradictory results and therefore are confusing. Here is what we can say at this point.


First and perhaps foremost, BA.4 and BA.5, like the other Omicron subvariants, cause less serious illness than the Delta variant or other previous variants. I believe that this is the most important point because what matters most is whether the severity of illness is getting milder or more severe. Speculation that Omicron BA.5 might be slightly more virulent that say Omicron BA.2, yet much less so than Delta, is not helpful in my opinion. Such speculation may make for eye catching headlines, but only serves to create anxiety which is likely unwarranted.


Overall, the mortality of COVID in the US has diminished substantially. Early in the pandemic, back in 2020, the COVID mortality rate in the US was around 2%. In some parts of the world it was as high as 6%, largely due to differences in availability of high quality healthcare. The current mortality rate from COVID in the US is estimated to be about 0.1%. This is due to several factors including the reduced virulence of Omicron, the immunity of the population through both vaccination and prior infections, and to some extend treatments such as antiviral drugs to prevent worsening disease in those infected. For comparison, the mortality rate for influenza in 2018-2019 was 0.02% in those above age 65 and 0.01% overall. During that time, there were 35.5 million cases of influenza in the US resulting in 34,000 deaths.


Omicron BA.2 remains the predominant variant in the US, currently at 62%, with BA.4 at about 8% and BA.5 at about 13% (the rest being a smattering of other variants). In the UK, Omicron BA.5 has surpassed the others and is now the dominant variant, so we may see that here in the US in the next few months. The advantage that BA.4 and BA.5 have over previous variants is likely due to further refinement of the spike protein acting as a better fitting “key” into the receptor “lock” that allows the virus to gain entry into host cells in the body. There is some discussion in the literature that maybe these variants are also slightly better at evading the immune system, but in my opinion that seems less likely. The other Omicron subvariants appear to be more susceptible to our antibodies not less. When Omicron first came on the scene, people speculated that its enhanced contagion could be from immune evasion. That turned out not to be the case. Evading the immune system requires a much more complicated set of mutations than simply selecting for a better fitting “key”. A point to keep in mind is that none of these changes suggest that the way SARS-2 is transmitted is changing. It is still primarily through respiratory droplets Thus, masking, social distancing and handwashing remain as effective as before.


A set of somewhat confusing science articles have recently come out arguing whether or not infection with Omicron boosts one’s immunity like we would expect and have seen with other previous variants. Some of the articles suggest that it does, while others maintain that it does not. To me, this doesn’t matter. We know that the COVID vaccines provide better and more sustained immunity than infection alone. While this may seem counter-intuitive, there are solid reasons that explain this. For one, the vaccines are designed to activate the immune system, while any invading virus is going to attempt to evade the immune system by nature. Also, the vaccines are designed to try to induce antibodies that will be effective against multiple different strains of the virus. So far, these vaccines are doing a very good job at preventing serious illness, hospitalization and death; which is what we want them to do.


The best strategies to continue to deal with COVID remain masking, avoiding crowds, handwashing and getting vaccinated. It really doesn’t matter which vaccine you get since the subtle differences between them are less important than getting vaccinated. To be fully vaccinated, you should get the first set, followed by a booster. If you are over age 65, then a second booster is also important.

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