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Can Nasal Vaccines Change the Span of the Pandemic?

Mucosal vaccines against COVID-19 have potential to avoid even mild infections and prevent transmission challenging current vaccines cannot address. But it’s too early to declare these vaccines — delivered nasally, orally, or transdermally — the answer which could quash the pandemic, experts say.

It’s still “start” for these immunizations, said William Schaffner, MD, an infectious diseases physician at Vanderbilt University in Nashville, Tennessee. There’s hope that intranasal vaccines can cut transmission, but “it’s more anticipated than demonstrated currently,” he said.

He along with other experts indicate too little data on the efficacy of mucosal COVID vaccines in humans and several challenges ahead for development and evaluation of efficacy.

At the very least 12 nasal vaccine candidates for COVID come in development, four which reach phase III clinical trials.

The only real approved intranasal vaccine of any enter the U.S. is FluMist, a live attenuated vaccine against influenza. Some countries, however, have previously approved mucosal vaccines for COVID. Earlier this month, China approved an inhaled COVID-19 vaccine as a booster and India gave the green light to an intranasal vaccine for emergency use, both predicated on adenovirus vectors.

Reaching Sterilizing Immunity

Like the majority of respiratory viruses, SARS-CoV-2 enters your body through mucous membranes like the mouth, nose, and throat. Following the virus makes contact on the mucosal surfaces, it multiplies, traveling from those entry points through the bloodstream to other areas of your body.

The theory is that mucosal vaccines could bolster immunity at these viral entry points, stopping the pathogen from implanting, multiplying, and transporting itself through the entire body.

“We realize that should you can induce immunity in the nose, that often is a lot far better in preventing infection,” said Kathryn Edwards, MD, a professor of pediatrics and vaccine researcher also at Vanderbilt University. “It’s a stylish hypothesis to believe we could commence to make weakened COVID vaccines that could be in a position to stimulate local immunity and really prevent infection.”

There’s some evidence accruing that higher degrees of mucosal immunity do that. For example, a study letter published in the New England Journal of Medicine showed that triple-vaccinated healthcare workers with higher degrees of anti-spike mucosal immunoglobulin A (IgA) had a reduced threat of a breakthrough infection with the Omicron variant (RR 0.35, 97.5% CI 0.11-0.91).

Current injectable vaccines, that assist prevent progression to severe infection and death, do induce some degree of mucosal immunity — but at typically suprisingly low levels, experts noted.

“Current vaccine strategies are actually effective and so are great at preventing disease,” said Benjamin Goldman-Israelow, MD, PhD, assistant professor of internal medicine and infectious diseases at Yale School of Medicine in New Haven, Connecticut.

“We think that further immunization and additional immunity within the respiratory system gets the potential to lessen transmission a lot more,” he said within an interview. “Could that further dampen the pandemic? Could it further inhibit viral evolution and the emergence of variants? Those things, we think, have become important.”

How Effective Are Nasal Vaccines?

Animal studies evaluating the efficacy of mucosal vaccines for COVID-19 claim that these vaccines might execute a better job at preventing infection.

Goldman-Israelow and colleagues tested intranasal vaccines in mice, showing a nasally-delivered, unadjuvanted spike protein booster that has been administered after an intramuscular mRNA shot induced mucosal immunity, both reducing viral load in the respiratory system and preventing lethal illness.

Additionally, Ahmed Hassan, PhD, and colleagues at the University of Washington in St. Louis, discovered that a single-dose, adenovirus-vectored intranasal vaccine reduced threat of infection in rhesus macaques in both upper and lower respiratory tracts.

A mix approach appeared promising in mouse-model research led by Matthias Tenbusch, PhD, of University Hospital Erlangen, Germany. An intranasal booster with adenoviral vectors induced high degrees of mucosal IgA and lung-resident memory T cells, enhanced mucosal neutralization of SARS-CoV-2, and provided complete protection against infection in mice.

“Our data thus claim that mucosal booster immunizations after mRNA priming is really a promising method of establish mucosal immunity along with systemic responses,” Tenbusch’s group wrote.

Biotech company Codagenix released phase I data on its live attenuated intranasal vaccine, CoviLiv, which showed a solid cellular immune and mucosal antibody response against Omicron BA.2.

However, there’s still hardly any data describing the efficacy of intranasal vaccines in humans. Focusing on how effective intranasal vaccines will undoubtedly be in preventing human infection and transmission will need to wait on phase III clinical trial results.

Obstacles to Development

Regardless of the promising premise, it will not be an easy task to assess clinical efficacy, said John Moore, PhD, professor of microbiology and immunology at the Weill Cornell School of Medicine in NEW YORK.

Determining correlates of protection — that’s, just how much of an immune response will prevent infection — is challenging in a population that is largely subjected to the herpes virus, he told MedPage Today.

“It is a worthwhile concept, but it will likely be challenging to prove that it is much better than what we curently have,” Moore said. He added that further research also needs to determine whether nasal vaccines will induce both mucosal and systemic immunity in a way that they may be used alone rather than only as a booster.

Additionally, it really is difficult to make a long-lasting and effective immune response with mucosal formulas. FluMist, for instance, was discontinued for an interval following recommendations from the CDC’s Advisory Committee on Immunization Practices (ACIP), after it had been been shown to be less effective than injected flu vaccines in kids over several seasons. Now, the vaccine is preferred for small children however, not for adults over age 49.

Gregory Poland, MD, a vaccine researcher at the Mayo Clinic in Rochester, Minnesota, put into the set of questions around these vaccines: Exactly what will durability and efficacy appear to be across age ranges? Will the antibodies generated neutralize all of the variants?

While intranasal vaccines for COVID certainly are a potentially great answer for crowded environments, like the military, college campuses or schools, Poland added: “Could it be the solution for infants and older adults, the people who are actually probably to be hospitalized or die? Unlikely without some type of scientific advance that hasn’t yet happened.”

Still, Poland said that getting a vaccine which could indeed block transmission could possibly be crucial to the general public health approach at this time of the pandemic.

“I believe that’s important if we are able to take action,” he said, noting that at the very least 100,000 people will probably die of COVID every year at the rate the herpes virus is spreading. “So yeah, blocking transmission? That might be a godsend.”

  • Amanda D’Ambrosio is really a reporter on MedPage Todays enterprise & investigative team. She covers obstetrics-gynecology along with other clinical news, and writes features concerning the U.S. healthcare system. Follow

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