Two inhaled covid vaccines have been approved—but we don’t know yet how good they are

The covid-19 pandemic is still not over. And while injected vaccines provide good protection from severe disease, they don't stop us from catching the virus or spreading it to others.

Vaccines that you inhale through the nose or mouth, on the other hand, potentially could.

In the last week, regulatory bodies in both India and China have approved inhaled vaccines for covid-19. The companies behind these vaccines say that they'll boost the immune responses of people who have already been vaccinated. Here's what we know so far.

What are the new vaccines?

On Sunday, CanSinoBIO, a biopharmaceutical company based in Tianjin, China, announced that its inhaled vaccine, called Convidecia Air, had been approved as a booster by the National Medical Products Administration of China. The vaccine is inhaled through the mouth, and the company says it can effectively induce comprehensive immune protection in response to Sars-CoV-2 [the virus that causes covid-19] after just one breath."

The approval was swiftly followed by that of another inhaled vaccine, developed in India. On Tuesday, Bharat Biotech, based in Hyderabad, announced that the company's nasal vaccine, known as iNCOVACC, had been approved in that country for restricted use in emergency situations," as a booster dose for people who have already had two doses of injected vaccines.

How do they work?

Both vaccines promise to induce an immune response in the linings of the airways-something immunologists call mucosal immunity. Once antibodies are present there, they should be able to provide a more immediate response to any virus entering the body via the nose and mouth, as the coronavirus can.

In theory, this type of immunity could prevent a person from becoming infected with the virus and from passing it to others. They're sitting where the virus is going to be encountered, which means they can act very, very rapidly," says Ed Lavelle, an immunologist at Trinity College Dublin in Ireland.

Do we really need more covid-19 vaccines?

We could do with better ways to protect ourselves from covid-19. While the number of covid-19 cases continues to decline-globally, weekly cases have fallen by around 12% in the last week-the virus is still responsible for many deaths. Last week, a person died from covid-19 every 44 seconds, Tedros Adhanom Ghebreyesus, director general of the World Health Organization, told journalists at a press briefing on Wednesday. Most of these deaths were avoidable," he said.

Will inhaled vaccines replace injected ones?

No. Injected vaccines tend to lead to the production of antibodies in a person's bloodstream and internal organs, which also provide a strong immune response to any invading virus. It's likely that the two vaccination approaches will work best when used together, says Lavelle.

Research in animals suggests that an injected vaccination followed by an inhaled one can provide the best defense against infection, in what's known as a prime-pull" technique. The injected vaccines prime the immune system, and the inhaled ones can give it an extra boost or pull. But Lavelle stresses that we still don't know if this approach will be as effective in people.

Which of the two inhaled vaccines is best?

We don't yet know. The two vaccines are administered differently-one through the nose and the other through the mouth. It's not yet clear which route might be best. In theory, vaccination through either route should trigger immunity in the nose, mouth, and upper airways, including the lungs. But protection will be strongest wherever the vaccine is delivered, says Lavelle.

Can inhaled vaccines help end the pandemic?

This is the big question, and unsurprisingly, there's no simple answer. In theory, if the vaccines can help prevent infections and transmission, they could have a huge impact on covid-19.

But there's a lot we don't know. We don't know how much protection the vaccines might offer, and whether the level of protection they provide will depend on which injected vaccine a person had in the first place. It depends on the duration of the response [in the body] and how much the virus is going to change over that period of time," says Lavelle.

We haven't seen all the data in terms of how effective [the inhaled vaccines are]."

Representatives of the World Health Organization echo his thoughts. Nasal vaccines could boost a person's first line of defense" against the virus behind covid-19 and have the potential to reduce onward transmission, Mike Ryan, executive director, WHO Health Emergencies Programme, told journalists at a press briefing on Wednesday. But it remains to be seen."