What COVID-19 Vaccine Booster Doses Mean for the Pandemic


Donald Alcendor, PhD, shares expert perspective on the newest FDA authorization, as well as what a full COVID-19 vaccine approval would mean for US immunization.

Donald Alcendor, PhD

Donald Alcendor, PhD

It will likely be a series of federal agency deliberations that define the next steps of US COVID-19 vaccination efforts, as the delta variant has driven new 7-day case averages above 100,000 18 months into the pandemic.

The US Food and Drug Administration (FDA) has granted emergency authorization for booster doses of already available COVID-19 vaccines for immunocompromised patients this week. There is also speculation that the FDA will fully approve Pfizer-BioNTech’s mRNA vaccine BNT162b2 before the end of August—an effort which experts have believed may encourage vaccination among the more hesitant US population.

In an interview with Contagion, Donald J. Alcendor, PhD, Assistant Professor of Cancer Biology at Meharry Medical College and Adjunct Associate Professor of Cancer Biology at Vanderbilt University School of Medicine, discussed the newest authorization for immunocompromised booster vaccine doses, the prospect of a full FDA COVID-19 vaccine approval, and what current metrics and interpretation of COVID-19 vaccine benefit mean for future strategies.

Contagion: What is the understood risk of SARS-CoV-2 infection and COVID-19 severity in immunocompromised patients?

Alcendor: The risk is great depending on the degree of immunosuppression. In a transplant patient, an untreated HIV patient, an elderly patient, patients under cancer therapy, or those with chronic disease such as chronic obstructive pulmonary disease (COPD), SARS-CoV-2 infection can have life-threatening consequences.

So, the risk would vary among patients. Many of these types of patients with managed disease that have received the vaccine have fared better than expected against COVID19 infection.

Contagion: Some experts have argued that the term “immunocompromised” is too broad to fit all eligible patients under this new authorization. Should there be a more specific prioritization of booster doses?

Alcendor: When the guidelines come out tomorrow, this term will need to be clinically defined, and patients should meet this clinical criteria. A person taking drugs for multiple sclerosis can suppress their immune system; will this allow them to get a booster? If you’re taking anti-inflammatory drugs that can suppress your immune system, will this allow you to get a booster? I agree the term is too broad and should be defined, with conditions and exemptions listed, by the FDA and CDC.

Contagion: Do you see the emergency authorization of a booster dose for immunocompromised patients to be a precedent for authorization of a booster dose for all fully vaccinated persons?

Alcendor: I think the precedent is precautionary based the potential poor immune responses to the vaccines that you might see in individuals that are immunosuppressed. They are more likely to have breakthrough infections that could lead to hospitalizations and death compared to folks who are not immunosuppressed and had good responses to the vaccines.

The delta variant is the main reason for this change, because the immunosuppressed population is most vulnerable and during the rise of the variant; we’ve seen more breakthrough infections and more pediatric hospitalization than before.

Contagion: What is your anticipated timeline for booster dose availability for the greater public? Could it potentially curb the delta variant outbreaks?

Alcendor: The FDA/CDC guidelines for a COVID-19 booster or third dose for individuals that are immune-compromised will likely be out (Friday August 13). Guidelines for boosters in the general population that are vaccine eligible are yet to be determined. Some individuals are lying about their vaccine status to get a booster and some folks that have money and private physicians will have ready access to booster vaccinations.

Contagion: The authorization does not extend to the Johnson & Johnson single-dose vaccine, which is still under review as a potential 2-dose option. What do you anticipate from their booster-dose data? Will it fare well similarly to mRNA products?

Alcendor: It is now recommended that if you received the Johnson & Johnson vaccine, you may have the option to get an additional dose of Pfizer’s of Moderna’s. Any booster with either another Johnson & Johnson dose or with a Pfizer or Moderna dose will potentiate your immune response and increase your protective antibody levels. You have to be concerned for individuals who had an adverse reaction to the initial vaccine dose because the second or third dose could be unpredictable.

Contagion: The FDA is also anticipated to fully approve Pfizer-BioNTech’s COVID-19 vaccine later this month. What do you see as the significance of a full FDA approval versus an EUA?

Alcendor: It is clear that once full approval is given for the Pfizer vaccine, I would expect a spike in vaccine uptake that will not last—but being at 61.3% of adults fully vaccinated, it will help. The vaccine now is eligible for licensure and that gives Pfizer important opportunities for expanded vaccine distribution and possible price increases for the vaccine.

Contagion: Much booster dose discussion has been hosted around waning immunity in early-vaccinated persons, with some debating the merit of changing vaccine efficacy rates in countries such as Israel. What are your thoughts on vaccine efficacy as a continued metric of COVID-19 mitigation?

Alcendor: It would be great to have a comprehensive study that examines antibody titers in serum from individuals that are immunocompromised and people that are not to gauge a protective antibody response and one that has waned to an unprotected level. There was a time when evidence suggested that 2 doses would last for years.

We do not want drug companies to dictate when and if we need boosters. We need a comprehensive study that demonstrates that antibody levels are falling below protection levels against the current variant. No one is discussing T-cell responses to the vaccines, which are just as important for protection as antibody levels to the virus.

Contagion: We recently passed 50% full COVID-19 vaccination in the US population. What are your thoughts on that count?

Alcendor: Because we have a surge in new infections that could take us back to where we were before in this pandemic, I am concerned that 50% is not enough. You still have more than 100 million people that remain unvaccinated in the US. We have longstanding poor vaccination rates especially in the South and Midwestern states that could prolong this pandemic until a dominant variant emerges that is nonresponsive to the current vaccines and renews this global crisis. Then we would have to start vaccinating people all over again with vaccine cocktails to account for viral variants.

This scenario would have grave global consequences.

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