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Experts say a nasal spray would attack the novel coronavirus at the point it enters the body. Petri Oeschger/Getty Images
  • Researchers say a nasal spray vaccine against COVID-19 might be the most effective way to fight the novel coronavirus.
  • That’s because the virus usually enters the human body in the nasal passage, and a spray would attack the invader there.
  • Right now, 7 of the 100 COVID-19 vaccines in clinical trials are nasal sprays.

SARS-CoV-2 is a respiratory virus, which means its favorite place to enter the body is through the nose. That’s why testing for the novel coronavirus involves nasal swabs.

If that’s the case, though, why do we vaccinate people against COVID-19, the disease caused by an infection with the coronavirus, with a shot in the arm and not a nasal spray?

Indeed, nasal sprays can be used to vaccinate against COVID-19, and several such vaccines are now being developed.

“One of the big selling points would be that intranasal vaccines are needle-free, and there is a big population of people who are freaked out by getting a needle stick,” Dr. Troy Randall, an inflammation, immunology, and immunotherapeutics researcher at the University of Alabama at Birmingham, told Healthline.

“Given that [the novel coronavirus] is a respiratory virus, having an antibody response in the nose is probably a better model,” he added.

Randall co-authored an article that was published today in Science magazine with fellow researcher Frances Lund on the potential benefits of an intranasal COVID-19 vaccine.

Delivering vaccines via a nasal spray is not a new idea.

FluMist, a nasal influenza vaccine, has been on the market since 2003.

Of the approximately 100 COVID-19 vaccines currently undergoing clinical trials, however, only seven are nasal sprays. And all COVID-19 vaccines currently approved for use are delivered via intramuscular injection.

Immunology researchers have learned in recent decades that the immune response to infections occurs not just throughout the body but also locally, such as in the mucous membranes in the nose and throat.

“To get that specialized response, you need to put the vaccine at the infection site,” Randall said.

The idea is to defeat the coronavirus while it’s still in the nose before it has the chance to invade the body further.

“You prevent the virus from getting a foothold,” he said. “A nasal infection won’t kill you, but you want to prevent an inflammatory immune response in the lungs that could.”

Vaccine shots, whether they use the cutting edge mRNA technology or a form of neutralized coronavirus, provide an immune response throughout the body, Randall noted, but only a relatively weak response in the mucosal lining of the nose, where most SARS-CoV-2 infections first take root.

Conversely, intranasal vaccines are potent at the site of administration but perhaps less so systemically, he said.

“From a public health perspective, it might make sense for everyone gets the shot in the arm initially and that the booster shot be the internasal one” so that a strong immune response is generated both locally and systemically, Randall suggested.

A vaccine that activates the immunoglobulin A and resident memory B and T cells in the nasal passages and upper airways not only would provide a barrier to infection but also reduce transmission of the coronavirus by immunized people who have a mild case of COVID-19.

Randall said that making effective COVID-19 nasal vaccines is complicated.

The most effective COVID-19 vaccines now being administered are based on cutting edge mRNA technology and include only bits of surface protein from the target SARS-CoV-2 virus, not an intact live or dead virus itself.

FluMist, however, delivers a dose of live attenuated (or weakened) influenza virus. That’s because “for it to work, it has to infect cells,” said Randall.

The COVID-19 nasal vaccines now being developed mostly work the same way.

Using live attenuated virus is an older method of vaccination and carries some risk of causing infection and illness in some cases.

The effectiveness of such vaccines can also be limited if the recipient has previously had the flu, since previously acquired immunity can destroy the vaccine before it can be recognized as a new strain of the disease.

Randall said that a nasally delivered mRNA-based vaccine is possible, but it likely would require tweaks to the coronavirus spike protein nanoparticles currently used in injectable COVID-19 vaccines.

“It needs to be formulated so that nasal epithelial cells will take it up and cause an immune response,” he said.