Covid’s Latest: Delta, EUA and Boosters

Forgive my hiatus; I have been working on my graduate project and have only recently finished it. Now that it’s submitted, I will hopefully be returning to more regular updates.

With the Covid-19 pandemic's recent lull and then resurgence, it is time again to talk about the most recent news regarding the pandemic. From my previous posts, let's take a look at what needs updating, what proved to be accurate and what we’ve learned.

Delta Variant

I’ve talked before about Covid variants and how they form. The Delta variant, otherwise known as B.1.617.2, was first detected in India in late 2020. It was declared a variant of concern by the CDC in June of this year and the WHO expects it to soon become the dominant strain of Covid-19 globally. The Delta variant has an R0 value calculated at between 6 and 7, which is more than twice as contagious as wild type Covid-19, though still lower than that of diseases like chicken pox and measles. There is data to suggest that the Delta variant causes more severe illness, with proportionally more patients being hospitalized compared to wild-type Covid or other strains, but this has yet to be definitively confirmed. It is safe to say, Delta has been a game changer in the pandemic fight.

The Delta variant poses the greatest risk to unvaccinated individuals, who have more severe illness and are more likely to transmit the disease to others. That said, there have been several thousand reported cases of breakthrough infections, where someone vaccinated against wild-type Covid-19 became sick with the Delta variant. The good news is that the vaccines still provide strong protection against the Delta variant, even if it isn’t airtight. Patients of breakthrough infections have far milder symptoms that resolve quicker and are less infectious for a shorter period of time. Fully vaccinated people account for less than five percent of Covid hospitalizations and very few Covid deaths.

The biggest risk created by breakthrough infections is that fully vaccinated people might be able to spread the variant to unvaccinated people. This transmissibility has the potential to create unique challenges. For example, many are worried that the next stage of the pandemic will be hyperlocal outbreaks. Due to the patchwork nature of Covid vaccination, especially in the United States, the country is divided between regions with very high vaccination rates and regions with very low vaccination rates. Because the Delta variant can be transmitted by vaccinated people as well as the unvaccinated, the virus can easily travel through vaccinated regions to reach these vulnerable pockets. Because the virus can be delivered to these vulnerable regions by asymptomatic carriers that are harder to trace, there could be more than one ‘patient zero’ for each mini-outbreak. This would create an accelerated outbreak; a lot of people would get sick all at once, overwhelming healthcare systems in the region before anyone could respond, before fading away again. By the time medical support could be mobilized for these vulnerable regions from other areas, most of the damage will already be done. It is the worry of some researchers that these hyperlocal outbreaks could be the new “normal” in this stage of the pandemic, especially given the low vaccination rates in some regions of the country.

Fortunately, the solution to preventing these outbreaks is simple; getting vaccinated. As stated above, vaccinated individuals are far less likely to catch the Delta variant and are even less likely to become severely ill from it. They’re also less likely to transmit the virus to others as they are less infectious for a shorter period of time. That said, the best way to prevent these hyperlocal outbreaks is to not have such a wide disparity in vaccination rates between adjacent regions. Accomplishing this will require improving vaccination rates overall.

Emergency Use Authorization

With the Pfizer vaccine recently gaining full FDA approval, the concept of emergency use authorization is in the news again. Vaccines that have been administered to millions of people are only now getting formally approved, so how safe can they really be? It is important to recognize that, while these vaccines getting full approval is certainly an important step, emergency use authorization still has very stringent standards.

I’ve talked before about the process by which drugs are developed and approved by health agencies such as the FDA. But to summarize, once a drug has been developed and tested on animals, it goes through three stages of human trials. Stage 1 uses a few dozen subjects at most and is to confirm the drug is safe. Stage 2 uses up to a hundred subjects and is to confirm the drug works. Stage 3 uses several hundred subjects and is to confirm the drug works on a diverse group of people and that it works as well or better than existing drugs. Data from all three studies is submitted to the FDA where it is reviewed before being officially approved. This process has been accelerated for Covid-19 vaccines but not in ways that reduce the vetting process. Typically, drugs are reviewed and approved on a ‘first come, first serve’ basis, but these vaccines were reviewed immediately. Furthermore, the separate stages for covid were done simultaneously, which would normally not be done due to the significant expense and far greater financial risk. And emergency use authorization was used to further accelerate this process.

The FDA created the EUA process in 2005 in order to accelerate the approval process for drugs that needed immediate use for emerging health crises. Drugs with EUA agree to a system of rolling submission to the FDA, where they submit the data from their clinical trials as it’s created instead of all at the end. It is important to note that both the Pfizer and Moderna vaccines were already well into their Phase 3 trials when they received emergency use authorization, and they agreed to share their data with the FDA as it became available. By this point, it would already have been known these vaccines were reasonably safe and effective, with the remaining data being used to confirm this beyond a shadow of a doubt. Emergency use authorization is also far easier to rescind than formal approval, allowing drugs that prove to be less effective than originally suspected to be quickly removed from general use. This is what happened to the drug hydroxychloroquine, which was given EUA in March 2020 due to some evidence of it having therapeutic effects, but was later rescinded in June 2020 when these effects were disproven. Standards for emergency use authorization are still very high, and the FDA pays close attention to the trials and data of these drugs to ensure they are safe and effective, and to quickly respond if they prove to be otherwise. This is a system designed to be fast, for when having a less tested drug is preferable to having no drug at all, but that is not the same as being completely untested.

Vaccine Distribution

There has been some recent debate on the use of booster shots for Covid. The Biden administration is recommending that those who’ve received two doses of the Pfizer or Moderna vaccines should receive a third dose about eight months after receiving their second dose. Evidence has consistently shown that antibody production to Covid-19 begins to diminish over time, which is why these vaccines use two doses. Now, whether or not this diminishing is fast enough and significant enough to mean that two doses isn’t enough to create long-lasting immunity has yet to be definitively proven. This policy around boosters is mostly based on being as safe as possible, as getting a booster shot will improve one’s immunity to some degree, making it harder for the virus to spread and hopefully ending the pandemic faster. That said, there is opposition to this booster policy, mostly from the WHO and others in the international community. The United States has some of the highest vaccine availability in the world, meanwhile there are countries that don’t have enough doses to begin vaccinating their front-line health workers. While a third dose would improve one’s immunity, it might not be by enough to justify giving a third vaccine to some when others haven’t even had one.

I could argue about the issues of wealth inequality that caused this uneven distribution, but the focus of this blog is on scientific policy. So I will instead talk about how this inequality directly hinders our ability to combat this pandemic. As we’ve discussed earlier, the more people in a given population that are vaccinated, the slower the virus can spread through that population. The faster a virus can spread, the less time it takes for mutations to occur which create new strains. This means that if one has a finite supply of a vaccine, it is a better use of that resource to distribute it as evenly as possible. If half of every country’s population was vaccinated, the pandemic wouldn’t be over, but the virus would be spreading far slower than before and new strains would have more trouble forming. But if half of the world’s nations were fully vaccinated while the other half wasn’t vaccinated at all, the pandemic would be over in some countries but still full force in others. And this full force pandemic would be the breeding ground necessary to create new strains that are resistant to existing vaccines, strains which could then spread to the fully vaccinated countries. It should be noted that the Delta strain originated in India, where the pandemic is still very much ongoing and vaccines are harder to come by.

If booster vaccines do become available to you, it is still wise to get one. There’s nothing to lose, something to gain, and it’s unlikely that an individual vaccine could be used somewhere else before it goes bad. But the methods for distributing these vaccines were not well-designed to deal with an actual pandemic, due largely to how inequitable these methods are. (This video from Vox goes into more detail about the corporate and economic policy of vaccine distribution). This is a good example of how public policy and social problems can impact health crises such as this one.

Covid Statistics

I’ll wrap this up with a few fun statistics regarding Covid-19 vaccines. An unvaccinated 18-29 year old’s chances of contracting Covid is 1 in 14*, and their chance of being hospitalized for Covid is about 1 in 237*, about the same as being dealt a straight in poker. By contrast, a vaccinated 18-29 year old’s chances of contracting Covid is 1 in 182*, and their chance of being hospitalized for Covid is 1 in 18,795*, less than one’s chances of being struck by lightning. The table below shows how these probabilities change depending on one’s age cohort relative to the 18-29 year old reference group (i.e. a 40 year old is twice as likely to be hospitalized than the 20 year olds these statistics were taken from).

As for the vaccines, both the Pfizer and Moderna vaccines are over 90% effective against wild-type Covid-19. (meaning that less than 10% of recipients will contract Covid and experience symptoms) The exact effectiveness rate against the Delta variant is still being determined, but it’s not believed to be any lower than 66%. Compare this to Salk’s first vaccine against polio, which had a 60-70% effectiveness against the most common strain of polio. Also, compare this to yearly flu vaccines, whose effectiveness can range between 10 and 60% each year. Again, these Covid vaccines aren’t airtight defenses, but they are comparable to other first generation vaccines and do offer significant protection.

*Based on statistics from the Indiana Department of Health.