At this point in the pandemic it is clear to everyone (or almost everyone) that vaccines work and are saving many lives. However, while their effectiveness in reducing hospitalizations and deaths is undeniable, they are not as effective in blocking the transmission of the virus – and that is why it is essential, even for vaccinated people, to wear a mask. This is because current vaccines, administered intramuscularly, induce the production of antibodies in the blood but not in the respiratory mucous membranes, where the virus can then replicate and be expelled by the vaccinated person via respiratory droplets or aerosols. As epidemiologist Michael Mina explains in a tweet (below), viruses such as SARS-CoV-2 do not need to replicate “internally” to retransmit, only locally: land in the nose, they replicate and are ready to move on to the next guest.
Stop definitivo. A possible stop to transmission could come from vaccines administered nasally (via spray or aerosol) which, as an Italian study explains, would be able to produce not only IgG (produced by current vaccines) but also mucosal IgA, thus succeeding to act not only internally but also locally in the respiratory tract. “It is very difficult to protect the upper respiratory tract with intramuscular vaccines,” explains Vincent Munster of the National Institute of Allergy and Infectious Diseases (NIAID). “Intranasal vaccines may be able to block the transmission of the virus,” says Martin Moore, co-founder of Meissa Vaccines, a Californian company that is developing such an anticovid vaccine.
The Meissa Vaccines vaccine uses an attenuated respiratory syncytial virus (RSV) modified to express the SARS-CoV-2 spike protein: “Hardly messenger mRNA vaccines (like those of Pfizer and Moderna, ed), they can become intranasal, ”explained Martin Moore, co-founder of Meissa Vaccines.
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Total protection. A recent study by Munster appears to confirm the ability of intranasal vaccines to induce both a systemic and mucosal immune response. This aspect, Munster points out, is of particular importance since aerosols from SARS-CoV-2, the coronavirus that causes covid, can lodge in both the upper and lower respiratory tract, triggering infection in the lungs, and immunity. mucosal would also ensure the protection of this area.
Phase 1 trial. Meissa Vaccines has just started phase 1 trials (on human volunteers), after the good results obtained with animal testing: the only phase 1 trial of an intranasal vaccine completed to date has not yielded good results, triggering a immune response much lower than hoped. It is that of the anticovid vaccine from Altimmune, a US biopharmaceutical, whose results were described by the director himself as “disappointing”.
However, according to Matthew Memoli (NIAID), the disappointment could be due to an inability to read the data: “The immune response triggered by intranasal vaccines will always be lower than that of intramuscular vaccines, but high levels of antibodies are not always synonymous with excellent protection against a disease ». According to Memoli, the basic problem could be the lack of knowledge of the functioning of the mucosal immunity of the respiratory tract, which would lead researchers to wrong conclusions and abandon promising vaccine trials too soon.