I have seen a few comments about the need for COVID-19 vaccine boosters before and after the appearance of the new Omicron variant. Of course, anti-vaxxers use this as a reason to deny the effectiveness of the vaccine. However, I’ve even seen pro-vaxxers misunderstand why boosters are needed.
Today, Pfizer announced that its preliminary studies showed that individuals who have received boosters produce about 25X more neutralizing antibodies against the Omicron variant than those who received the COVID-19 vaccine alone. This is awesome news with the caveat that this has not been peer-reviewed or published, it is just a report from Pfizer itself. In the hierarchy of vaccine research, it is pretty low until it is published in a medical journal.
I’m going to try to explain the reasoning behind the need for COVID-19 vaccine boosters against the Omicron variant. I hope it provides some science-based facts about boosters so that it might help you in discussions about the vaccine and new variant. I’m dividing my explanation into three broad areas, with the intent to make the science as clear as I can.
And just to remind everyone, I am fully boosted with the Moderna vaccine.
First, why are the COVID vaccine boosters so powerful against Omicron?
As I wrote above, individuals who had received a Pfizer vaccine booster had 25X more neutralizing antibodies than those who had just received the typical two doses. Neutralizing antibodies are the powerful first line of defense of the immune system to render a pathogen to be no longer pathogenic or infectious. Neutralizing antibodies are part of the adaptive immune system and they stop infections by binding to the SARS-CoV-2 virus, preventing it from entering the cell.
Vaccines (or “natural” infection) do not induce an immune response to the whole virus — the adaptive immune system recognizes pieces of the virus called antigens. Antigens are usually bits of glycoproteins or proteins that are on the surface of the virus which is unique to that virus. Viruses don’t usually have one antigenic site, they may have hundreds, but a vaccine only has to train the immune system to recognize just a few.
Variants, such as Delta and Omicron, have numerous mutations that might change the antigenic site, which means the immune system may not be able to attack the mutated virus, and it remains pathogenic and infectious until the immune system is able to produce antibodies against the antigenic sites on the variants.
Booster shots also do something else amazing with the immune system — they can increase the number of antigenic sites on a particular virus that neutralizing antibodies can “read.” Since the Pfizer mRNA vaccine only produces the spike protein, each subsequent vaccination allows the immune system to read more and more antigenic sites on that protein. And most of those sites may not have mutations, so as the adaptive immune system gains more information (yes, the immune system is like a giant computer in some sense), it is able to ignore mutations and still recognize other antigens on the spike protein.
So, the booster does one important thing — it teaches the immune system to recognize more and more antigens on the SARS-CoV-2 virus that causes COVID-19. And that makes the vaccine more powerful even against new variants like Omicron and Delta.
Second, why do vaccines wane?
Immunity from vaccines does wane over time. And it seems likely that vaccine-induced immunity against COVID-19 seems to wane fairly quickly, as compared to tetanus or measles vaccines which take decades to wane.
And in case you’re wondering, yes, “natural” immunity in those individuals who contracted COVID-19 also experience waning immunity. Do not believe those tropes that natural immunity is inherently better than vaccine immunity. And you can believe that a COVID-19 “natural” infection is substantially worse than the rare and mostly minor risks from the vaccine.
So, why do the COVID-19 vaccines wane?
Neutralizing antibodies do not have long-term staying power. Levels of these molecules typically shoot up after vaccination, then quickly taper off months later. The COVID-19 pandemic is such that we are in almost constant contact with the virus, so neutralizing antibodies are critical.
But neutralizing antibodies are only ⅓ of the immune response to the virus. The cellular immune response, which includes the other two parts of the immune response B cells and T cells, is what really does the hard work against the virus.
Memory B cells, which can rapidly deploy more antibodies in response to re-exposure to SARS-CoV-2, tend to stick around a lot longer. The same can be said T cells, which attack cells already infected by the virus. They are the second and third lines of defense if neutralizing antibodies fail.
Research has found that the vaccines really pushed durable cellular immunity. Memory B cells continued to grow in numbers for at least six months and got better at fighting the virus over time. T cell counts remained relatively stable, dipping only slightly over the duration of the study period.
And this is why those who are vaccinated, even if they contract COVID-19, have shorter and less severe cases of the disease. The initial antibody response does wane, but the cellular responses actually get stronger. So whenever there is a breakthrough infection, the B and T cells fight the virus before they can do serious damage
In effect, the boosters are really useful in “boosting” the neutralizing antibodies, preventing even a minor breakthrough infection. And that seems to wane over time. But the more powerful cellular immune responses, from B and T cells, seem to get stronger.
Third, are boosters going to be a way of life?
Based on what I wrote before, it may seem that we could survive without the neutralizing antibody response because their good friends, the B and T cells can clean up the mess.
However, the problem is that even though a fully vaccinated person (with two doses) might only have weaker effects from COVID-19, they still can spread it to unvaccinated individuals. And viruses that reproduce also can mutate, which could produce a new virus that avoids all three parts of the immune response.
So it appears that those who have received COVID-19 vaccines may require boosters against the Omicron variant.
Remember something important — vast areas of the world remain under-vaccinated. And those areas may have endemic SARS-CoV-2 which means they become reservoirs for new variants.
I don’t work for Pfizer (or Moderna, JNJ, AstraZeneca, or any other company producing vaccines), and I am not a scientist in the CDC or WHO. So I can only put on my science hat and tell you what I think.
Pfizer has indicated it’s working on a vaccine update to deal with the Delta and Omicron variants. We might need that booster for both the antibody and cellular immune responses. That will help stop Delta and Omicron from reproducing and thereby mutating to a new strain.
But we might also need to keep boosting to maintain an adequate neutralizing antibody response to the virus.
My best-educated guess is that we’ll need annual (maybe even semi-annual) booster shots, irrespective of the vaccine you received. We’ll need to do this until the moment someone declares COVID-19 extinct, and it may never reach that point.
The optimal result is that we treat COVID-19 like the most dangerous flu ever — new vaccines come out every year to deal with the newest variants. And we can live a normal life, as we do with the flu.
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