COVID-19 Vaccine’s Efficacy-Distribution Tradeoff

We interview epidemiologist Dr. Yulin Hswen at UCSF to better understand where our vaccines are falling short, and why.

Written by Siona Prasad and Anshya Tewari

After contracting the flu once, we are unlikely to get the same strain again. Even if we do, the consequences are minimal and the chances of getting it a third time are exponentially diminished. 

Our immune system has an excellent memory for disease. The first time we are exposed to a particular pathogen, our adaptive immune system takes time to recognize the threat and mount its response. The second time, not only can our immune system recall defenses to protect us quickly, but it is also able to recognize that this threat is common and ensures that it is continuously protected against. 

The strength of the secondary response—the combination of disease memory and active protection—is the basis of many double dose vaccines.

The strength of the secondary response—the combination of disease memory and active protection—is the basis of many double dose vaccines. Vaccines capitalize on the body’s natural way of building immunity by exposing individuals to a weakened form of the virus or, in the case of mRNA technology, a harmless portion of the virus. With a second dose, vaccines aim to expedite the path to secondary immunity.

The COVID-19 mRNA vaccine is one such two-dose vaccine. Both the Pfizer and Moderna vaccines recommend that people get two vaccine shots to maximize protection, with a 3-4 week interlude between each dose. 

The mRNA technology works by giving our bodies a set of instructions to manufacture the spike protein, a unique but harmless portion of the coronavirus that is responsible for allowing the virus entry into cells. By relaying these instructions, the vaccine is able to teach the immune system how to defend itself.

When the vaccine came out, the science behind the new innovation captured the narrative. After months, we finally had a vaccine—and an impressively effective one at that. The efficacy numbers were correspondingly high. Pfizer’s novel mRNA technology, combined with the secondary immunity conferred through two doses resulted in efficacy numbers as high as 95%. Moderna came in a competitive second of 94%. Amidst the turmoil, these efficacy percentages were thrown around with no interpretation apart from what we garnered from pitting the vaccines against one another. 

Amidst the turmoil, these efficacy percentages were thrown around with no interpretation apart from what we garnered from pitting the vaccines against one another.

We interviewed Dr. Yulin Hswen, Assistant Professor in the Department of Epidemiology and Biostatistics and the Bakar Computational Health Institute at UCSF, and coauthor of a recent paper on factors associated with likelihood of taking a vaccine to better understand these percentages. 

Dr. Hswen’s first response—the numbers aren’t enough. “You need another equation—a true efficacy of sorts, a measure of the vaccine’s effectiveness combined with the rate at which it is reaching people.” After all, considering these numbers in the absence of the vaccines distributability was meaningless. In a recent study, Bloomberg News found that only 36% of doses delivered to states have actually been administered. The other 64% discarded.

Designed by Wamia Said

The unfortunate truth is that these vaccines, while effective, pose a significant logistical challenge: They must be stored at cold temperatures to maintain viability. Keeping the Pfizer vaccine at -70 degrees Celsius and Moderna at -20 degrees Celsius makes them hard to store and transport. When temperatures around the vaccine rise, enzymes that break down RNA become more active, rendering the mRNA basis of the vaccine mechanism virtually useless. Moreover, once these vaccines are thawed, they must be used or disposed of within 24 hours. It is unsurprising that rollout of a two-dose, high maintenance vaccine poses a series of compounding problems. 

Dr. Hswen emphasizes that “there is already difficulty with getting the first dose, not only due to general hesitation but also logistical issues, going to the clinic, leaving work, geographic closeness, other barriers. There is bound to be attrition for the second round.” 

Furthermore, she discusses that “another reason for attrition is the possibility of a side effect reaction to the vaccine. Having a negative reaction the first time, you may be potentially discouraged to take the second dose.”

If a two-dose vaccine created so many logistical issues, this raises the question: would it have been better to have a vaccine with lower efficacy, perhaps only a single dose, but had it out earlier and made it more widely available? 

Dr. Hswen quotes, “The faster and earlier we can distribute some level of immunity, the better we would be able to reduce the spread, number of cases and deaths.”

Flu vaccines have efficacies in the 60 to 70 percent range, yet with the COVID-19 vaccine, numbers as high as 95% were the standard to obtain. If other vaccines have successfully weathered outbreaks with much lower efficacies, why did we spend so long striving for these high numbers?

Dr. Hswen asserts that the issue is more nuanced. “A really big reason why they push for high vaccine efficacy is because of the general polarization of people’s attitudes towards vaccination. People from our survey showed that they would not take the vaccine if it wasn’t higher than a certain percentage. [Public health officials] felt that if they went to a lower range of efficacy, it would stunt distribution in the way of people not wanting to take it.” In short, there was so much scrutiny on this vaccine that public health officials felt that people weren’t going to take it unless it reached a certain threshold of efficacy.

There is such a difficult tradeoff between distributional ease and effectiveness that we face with this vaccine. On one hand, people want over 90% efficacy—a piece of scientific genius delivering that coveted level of secondary immunity. On the other hand, it is these very innovations that are reducing accessibility and distribution. As Dr. Hswen puts it, “this is public health — it is about ensuring populations are saved.”

Dr. Hswen reminds us that these shortfalls—our prioritization of a high efficacy rate over widespread accessibility is indicative of an entire host of other issues with medications. “What about insulin care for diabetics? What about basic cardiovascular care? What other aspects of healthcare are being stunted by our priorities lying in the wrong place?”  The vaccine response to the COVID-19 pandemic must be used as an opportunity for us to understand that proclaimed levels of efficacy and innovation for this vaccine—or any other medication—mean nothing if they fail to reach the people who need it. 

Edited By: Wamia Said

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