Coronavirus news & views

Paxlovid: Just Follow The Settled Science

“We will see…”

-Yours Truly

Precis: “Just follow the science.” “The science is settled,” etc. We have all heard these bromides only to be later instructed that we need to follow a different science truth, or that the science firmament has shifted. Frustrating isn’t it? You must think that scientists must be a wad of weasely, waffling, wags in white coats certain of only uncertainty. One day we sagely advise you that something is certain truth, the next day we say that new research says that something else is true because, well, we know and you just need to trust us. We know because we did those ephemeral, sacred rituals called studies that give us all-knowing wisdom that we then impart to you who should worship us. 

That, I hope you know, is the cynical view of science, which sometimes is deserved. But, there is another side of things, which should be heeded. That side is that everything technology-based; from medicine, sanitation, lights, electricity, cell phones, transportation, etc.; that we enjoy using and take for granted, was created by that same science. These two sides of science often collide and greatly confuse non-scientists, which is most people. That is a shame and that is why I blog—to try to reduce some of the confusion.

Paxlovid, a drug highly touted as the only oral medicine to treat COVID is a great example.

Backstory: Paxlovid was initially given emergency use authorization (EUA) for treating COVID by the FDA in 2021 because of promising preliminary observations. Clinical trials performed by its manufacturer, Pfizer, then quickly showed solid, eye-popping results that made the drug an overnight sensation. It demonstrated an 89% reduction in the risk of hospitalizations and deaths in infected individuals. It also shortened the disease and reduced the symptoms of those with mild to moderate COVID. All this lead to the NIH to prioritize it over other COVID treatments under investigation at the time. In other words, NIH put R&D on other potential anti-COVID drugs on the back burner because they had found an effective one.

Paxlovid was the first effective oral anti-viral treatment for COVID. It basically works by blocking a key enzyme the virus uses to make new virus particles. A second medicine in the drug is an old treatment for HIV/AIDS which affects liver metabolism of that key enzyme blocker allowing it to linger longer, thereby boosting its antiviral effect.

The only drawback to Paxlovid is that it needs to be started shortly after infection to be effective. It also interferes with several common medicines so some patients either have to forgo taking some of their regular medications for a while or avoid Paxlovid. Nevertheless, it has been quite beneficial for reducing COVID symptoms in infected people and preventing severe COVID disease.

What is new? Ok, now you can forget everything about Paxlovid you read above. A new clinical trial, also done by Pfizer, and just published in the New England Journal of Medicine, showed that Paxlovid does not help patients get symptom relief or reduce the incidence of severe COVID and hospitalization. In other words, Paxlovid had zero effect on COVID in the study just published.

Thus, the makers of the drug now have two studies with diametrically opposite results on the effects of Paxlovid on COVID patients. The first showed “eye popping” effects sufficient to get NIH to move all other drug investigations to a lower priority. The second showed that Paxlovid was no better than a placebo.

At this point, I suspect many readers are rolling their eyes and thinking this is just another example of “settled science” unsettling the “suckers” who listen to the weasely, waffling, wags in white coats. Well, unroll your eyes. Both results are right.

Say what? Yes, it is likely that both results are accurate because the two Paxlovid studies were done on quite different populations.

The first study, which showed a dramatic positivie effect of the drug was done pre-vaccination. The study population did not have the advantage of vaccine protection against COVID. The second study was conducted post-vaccines and the participants had the advantage of already being partially protected against severe COVID symptoms. That protection rendered the Paxlovid effect meaningless. It showed that the the drug doesn’t do much if you have been keeping up with your vaccines, and it shows the value of the vaccines.

Kudos to Pfizer for conducting and publishing the results of both studies, especially the second one. The results of the second study certainly will ding Pfizer’s bottom line, but it was an exercise in honest science. Still the results of the study do not leave Paxlovid totally off the COVID treatment radar. First, the study did not indicate that the drug is ineffective for high risk vaccinated patients, such as immunocompromised patients. And in the US, we still, unfortunately, have many un- and under-vaccinated people who would benefit from Paxlovid when they catch COVID. Finally, while this Pfizer trial involved about 650 test subjects, a much larger trial involving a few thousand subjects soon will be forthcoming from the UK.

So, if you are vaccinated and catch COVID, it is not crucial to get to your doctor in time to get on Paxlovid. And the UK trial might address additional questions that will tell us more about the value of Paxlovid in treating COVID. We won’t know until its study results are released. In other words:

We will see.

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Why Don’t The COVID Vaccines Last Longer?

The FDA just authorized a second booster shot of the Pfizer-BioNTech and Moderna coronavirus vaccines for people over 50 and the CDC has approved it. A second booster has already been approved in the U.K., Sweden, Israel and Denmark.

Why do we need a second booster only months after the first booster, which came only months after most of us received two jabs of either the Pfizer-BioNTech or Moderna mRNA vaccines? Are the vaccines not very good? After all, we get small pox or measles shots that last a lifetime. Others, like the vax for tetanus, last for ~10 years. Why can’t we get a more durable coronavirus vaccine?

The answer is complicated and largely rooted in both viral biology and vaccine immunology.

Viral biology. The simplest answer is that viral mutation can change the molecules the vaccine immune response is trained to recognize, causing vax immunity to decay as viruses mutate. The coronavirus vaccines are directed against the spike protein expressed on the original CoV-2 that first appeared in Wuhan, but that ancestral bug has spawned mutated progeny that look a bit different to the immune system. In other words, viral variants created by “antigenic drift” become less recognizable to the immune system. That is why the vaccines are somewhat less effective against the Omicron variant that carries numerous point mutations in its spike protein. The current vaccines are still pretty effective against current viral variants, but continued antigenic drift along with the selection of variants that can better avoid vaccine immunity will likely require new vaccines in the future.

So, why do we need new flu vaccines every year, and need frequent CoV-2 vaccines, but we don’t similarly need new measles vaccines? Measles, mumps, flu, COVID, and other diseases are caused by viruses, but the different viruses behave quite differently. Viruses carry relatively little genetic material that tends to mutate as they replicate and spread. Some viruses, like flu, also have a “segmented genome” meaning that their genetic material is carried on several separate genetic molecules, making it easy to shuffle their genomes like a deck of cards when different flu strains infect the same animal. Other pathogens carry all their genetic material on a single DNA or RNA molecule making such gene shuffling between strains less likely, but it still happens. Also, the mutation rate of a pathogen’s genome is a function of its replication rate; hence, each time a bug copies its genome, small random errors are inserted into its genetic code. The more the bug replicates, the more mutations will accumulate in its genome and the faster replicating bugs will more rapidly create new variants. Thus, the measles virus is pretty stable since it does not replicate as much as a coronavirus or a flu virus, so it is not surprising that vaccine immunity to measles is much more durable. Smallpox and polioviruses also have relatively low replication rates and vaccine immunity to them also is long-lasting. In contrast, flu and coronaviruses replicate rapidly and pass back and forth between humans and animals. This means that they mutate rapidly and need frequent vaccine updates.

Other vaccines, such as the TB vax, target bacteria not viruses. Bacteria carry larger genomes that are not so changeable, so anti-bacteria vaccines also are pretty long-lasting compared to many anti-viral vaccines.

Yet other vaccines, such as those against tetanus, diphtheria, and pertussis do not even target the pathogen at all, but target toxins produced by the bugs. Vaccinated people produce antibodies that neutralize the toxins and this prevents disease. These vaccines do not forestall infection, they simply prevent the ill effects of the pathogen. Therefore, for these toxoid vaccines, there is no immunological selective pressure to select pathogen variants that can avoid vax immunity. Vaccines against these toxins also tend to be among the longest-lived vaccines.

Vaccine immunology. Vaccines aim to mimic natural immunity we develop to infection with pathogens. By exposing the body to harmless imitations of a pathogen, vaccines create an immune response and immune memory against pathogens, while avoiding the disease caused by the bugs. When an infection does occur in a vaccinated person, a rapid and robust immune response is mounted, first with B-cell generated antibodies that latch onto the invaders and prevent them from spreading and causing illness. Then T-cells secret cytokines that further ramp up the inflammatory response, and other T cells attack pathogen-infected cells. As explained earlier in these pages, antibody responses tend to linger only a few weeks to a few months and then gradually decay. This is good; otherwise your blood serum would be like syrup from all the antibodies against all foreign things you encountered over your lifetime. While antibodies circulating in your blood are good for quickly attacking infections shortly after infection, they do not confer long-term immunity. What confers long-term protection is what are called memory cells. These are a relatively few T and B cells that go dormant after fighting an initial infection or responding to a vaccine, but hang around awaiting a new infection to signal them to quickly roar back to life and mount a vigorous response against their cognate pathogen. This secondary response to a previously seen pathogen is much faster and usually nips the bug in the bud so you don’t even know you were infected.

When we hear that CoV-2 immunity decays only a few months after vaccination, the reports usually refer to declining levels of anti-CoV-2 antibodies, which happens naturally. Such announcements do not take into account your immune memory, which is harder to measure, but which is a better metric of your long term immunity. The problem also is that we simply have not had enough time with the vaccines to know how long their immune memory persists. It seems relevant that a study published in July 2020 reported that people who were infected with SARS in 2003 maintained robust T cell immunity 17 years later. So far, indications are that even though antibody levels fall over time, immunological memory after vaccination also remains robust. This is seen by the continued protection from serious disease and death in vaccinated people with low antibody levels. The vaccines and the immune memory they stimulate are working. How long that memory persists is unknown. Time will tell.

So why are we getting the booster shots? In the face of a raging pandemic caused by a novel pathogen, the cautious approach is to keep antibody levels at a protective level in vaccinated people until we better understand the extent of long-term protection brought on by our immune memory. The boosters, therefore, represent a cautious approach to maintain an effective antibody defense during these still early months of a novel pandemic. We likely will reach a time where world-wide immunity from vaccination and natural infection will give us baseline protection that will render COVID-19 mostly a bothersome disease rather than a life threatening infection. Until then, the boosters are a good idea to help us maintain an effective antibody defense against serious disease.

The natural pathology of measles is instructive here. Even though antibody levels typically decline after most immunizations, antibodies produced after a measles vaccine persist for many years. This happens with some other, but not all, vaccines too, but why? In countries where the measles virus is endemic, repeated infection of vaccinated people keeps the antibody immune response in continual high gear. That is not the case with the flu virus which changes rapidly and bypasses last years shot. Interestingly, measles has been eradicated from the US and Western Europe, so vaccinated people are not continually exposed and re-exposed to the virus and, unlike for those who live in endemic areas, our anti-measles antibody levels decline. Therefore, our long-term protection against the virus is due to our immune memory and not due to antibody levels.

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Updated: Over 65? Roll Up Your Sleeve Again

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The Washington Post just reported that Pfizer and its partner-in-vax, BioNTech, plan to seek emergency authorization for a second CoV-2 booster for those of us 65 and older (you know who you are). It is intended to beef up immunity that wanes a bit a few months following the previous booster.

US data show protection against severe COVID illness is robust after the first booster, but falls somewhat from 91 percent effective in preventing severe illness to 78 percent effective over several months. Still, 78% protection is very good, but given how transmissible Omicron is, and the possible emergence of the Son-of-Omicron, which might be even more infectious and virulent, the idea behind a second booster is to offer people the chance to acquire the greatest level of protection possible. Not a bad idea.

The data that will be submitted to the FDA in support of the 2^nd booster probably will include real-world data collected in Israel, which has already rolled out the second shot, and has reduced infections and serious illness in people older than 60. This will likely not be the last CoV-2 vax we will see. Pfizer and BioNTech are also working on a vaccine more effective against all variants and provide more lasting protection. That remains on the horizon, so stay tuned.

For those of us 65 and older, we (at least the males in that demographic) remember draft cards. As we entered our later years, the draft card, if unburned, was replaced in our wallets with our AARP cards, and then accompanied with our Medicare cards. Now we need a new wallet pocket to accommodate our vax card.

On a personal note about cards, your maturing and slowing bloggeur admits favoring a certain grocery store in town because they still card him when he buys his bottles of 80 proof anti-vax remedies.

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Update: Three days after this was first posted, Moderna announced that it also has asked for FDA approval for a second booster. However, they ask that the booster be approved for all adults over 18, and not just for those over 65 as Pfizer/BioNTech have done. This request, like the one submitted by Pfizer/BioNTech is largely based on recent data from Israel. 

Moderna made a strategic decision to request approval for all adults in order to give the FDA flexibility in deciding which patients would be good candidates for the booster. In other words, they could decide that it also would benefit under 65 and so recommend.

 

 

Unvaccinated People Are 11 Times More Likely To Die Of COVID-19

People who were not fully vaccinated this spring and summer were ~10 times more likely to be hospitalized, and 11 times more likely to die of COVID-19, than those who were fully vaccinated, according to one of three major studies published mid-September by the CDC.

That study did not distinguish between which vaccine the vaccinated cohort received. But, a second study compared the different vaccines and found that the Moderna vax was somewhat more effective in preventing hospitalizations than the Pfizer and J&J vaccines. This assessment was based on the largest US study to date of the real-world effectiveness of all three vaccines, involving about 32,000 patients seen in hospitals, emergency departments and urgent-care clinics across nine states from June through early August. While the three vaccines were collectively 86 percent effective in preventing hospitalization, protection was higher among Moderna vaccine recipients (95 percent) than among those who got the Pfizer (80 percent) or J&J vaccines (60 percent). That finding echoes a smaller study by the Mayo Clinic Health System in August, which showed the Moderna vaccine to be more effective than the Pfizer vax at preventing infections from the Delta variant.

Vaccine effectiveness against infection dropped from 90 percent last Spring, when Delta had not yet gained significant traction, to less than 80 percent from mid-June to mid-July, when Delta began out-competing other viral variants. Importantly, effectiveness against hospitalization and death showed barely any decline during the entire period. Thus, all vaccines remain quite effective and useful in protecting against illness.

Get one!

Why there is a difference in preventing infection between the Pfizer and Moderna mRNA vaccines was discussed earlier in these pages.