Expert: COVID-19 Vaccination Does Not Completely Protect Against the Virus’s Impact on Taste, Smell Function


Kai Zhao, PhD, director of the Nasal Physiology and Therapeutic Center in the Department of Otolaryngology at Ohio State University College of Medicine, discusses his research investigating the persistence of taste and smell loss among patients who have been infected and reinfected with COVID-19.

Pharmacy Times interviewed Kai Zhao, PhD, director of the Nasal Physiology and Therapeutic Center in the Department of Otolaryngology at Ohio State University College of Medicine, on the dangers of the loss of taste and smell among patients who have been infected with COVID-19.

Alana Hippensteele: Hi, I’m Alana Hippensteele with Pharmacy Times. Joining me is Kai Zhao, PhD, director of the Nasal Physiology and Therapeutic Center in the Department of Otolaryngology at Ohio State University College of Medicine and senior author of a study recently published in Med that showed that a loss of smell and taste is a common COVID-19 symptom that may persist for longer than patients even realize.

Why did you and your colleagues conduct this investigation into the persistence of the loss of taste and smell for patients who have been infected with COVID-19?

Kai Zhao: Shortly after COVID-19 had become a global epidemic, there had been reports [that came] out quickly that smell and taste loss may likely be a major symptom of COVID-19, which is very intriguing for us, as we're smell and taste researchers, and smell loss is not that common among upper respiratory viral infection.

For example, cold and flu, only a small percentage will have smell and taste loss, but for COVID-19 it’s significant. So, that actually drove us to really doing research in this area. By the time last year when we had a new variant come out, Delta, which was widely spreading and overtaking the previous variants around globally, people had anecdotal reporting that Delta may have a less or different impact on taste or smell. So we thought that was interesting. So we continued our surveillance on [these symptoms among] patient populations.

Also by that time, I think around April, vaccination was widely available to the US, and more and more of the general population was vaccinated. So there was a hope [that] in adults vaccination can impact the virus’s [effect] on taste and smell malfunctions, as it does for severe infection, hospitalization, and death. So maybe vaccines can protect us.

So that's the reason why we did this data analysis based on our continuing monitoring of populations in Columbus, Ohio, and we actually found that most of our patients [with smell and taste loss] were fully vaccinated, and the infections occurred during the peak of the Delta variant, and almost all of them had a high prevalence of objective smell and taste loss. So it seems that the Delta variant at least has a very strong impact on smell and taste function, and also vaccination cannot completely protect us from the virus’s impact, at least on the taste and smell function.

Alana Hippensteele: As a follow up to that, patients who experience that symptom would that potentially be the only symptom [they experience], or did you find that fully vaccinated patients who are infected with COVID-19 and experienced that smell and taste loss had other symptoms as well?

Kai Zhao: Yes, they do have other symptoms. So majority of these patients have 2 to 8 other different symptoms. Although I would want to say that I want to point out that none of our patients, at least in this polling study, are being hospitalized. So [for these patients] it is generally considered mild disease, but majority of them had more than one symptom other than smell and taste loss.

Alana Hippensteele: If COVID-19 shifts from being a pandemic to being endemic, like the flu, what are the implications of some of these more persistent symptoms on populations?

Kai Zhao: Yeah, I think that's a very good question. So we don't really know that. If I would speculate, I think it would—just like flu—there could be multiple strains of COVID-19 spreading around globally and maybe have seasonal changes.

For example, the focus of our previous studies on Delta, we know that now Omicron is dominant, even Omicron BA.4 or BA.5 are dominant in circulation, but we don't know if Delta may come back or not. We have some reports that Delta is still circulating with very low incidence rates in the community, and there is very limited cross immunity between Delta and, for example, Omicron. So we really don't know how, when the pandemic is transitioning to endemic, whether or not different variants work by recirculating seasonally in a varying fashion, just like the flu.

Also, we know that vaccination or even prior infection potentially cannot protect smell and taste function from the virus’s effect, just like flu and cold. We may repeatedly get COVID-19, and we may have smell and taste impacted by the infections. So, I think this will become a very large public health problem that you will have among certain populations that get repeated infected by the virus, and there could be ongoing smell and taste loss throughout the population of a much higher prevalence than we see for flu and cold. So, that will be a public health concern for the future.

Alana Hippensteele: What are next steps in your research in this area?

Kai Zhao: Well, we are still monitoring active infection in our local populations, we're still continuing to test patients for Delta even during the Omicron period, and we are still trying to publish these results. Also, we’re focusing a little bit more on the long COVID-19 complications. So at Ohio State University, there is a long COVID-19 clinic, and we collaborate with these clinics to recruit patients who have ongoing smell and taste loss and to assess their recovery and see if any mitigation can help their recovery.

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