Why mucosal immunity may be required to end the pandemic
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Following the recent emergency use authorizations of multiple vaccines for COVID-19, the first wave of people have already begun the vaccination process — a truly remarkable milestone. As someone who has dedicated his career to drug development and discovery focused on viral vectors and antiviral therapies, I can tell you that the science has moved fast, and we have every reason to celebrate. The data on these vaccines are good. They are well studied and their potential for public health is promising.
However, I can also tell you that this is likely only the beginning. I worry that the rollout of the current vaccines will create a false sense of security among a large population of people. There is a scenario that we need to be prepared for and one that could possibly derail our fight against this virus: These first-generation vaccines will be able to effectively block disease, but not the transmission of the SARS-CoV-2 virus.
Pfizer, Moderna and nearly every other pharmaceutical company are producing injectable vaccines. Their protective power results from systemic immunity, meaning that they generate antibodies that circulate in the blood to other parts of the body. They were authorized based on their ability to block the development of disease, which is not the same as the ability to inhibit viral infection or transmission.
The best way to block both viral infection and transmission is by inducing a special type of immune response called mucosal immunity. Mucosal immunity protects the parts of the body that are in contact with the environment, and in the case of a respiratory pathogen, that means the nasal cavity and the lungs. Because it is a localized type of response, a vaccine needs to be delivered to the appropriate compartment if mucosal immunity is to be stimulated. In the case of a respiratory pathogen like SARS-CoV-2 that means intranasal vaccine administration.
Without mucosal immunity, the virus may continue to thrive in a person’s nasal cavity allowing for easy transmission. This is why wearing a mask, even after vaccination with an intramuscular vaccine, will remain critical.
Thankfully, scientists, including our team, are working on next generation vaccines that can elicit mucosal immunity, including intranasal vaccines that have the potential to elicit an immune response in the nose as well as systemically. This type of broader immune response could defend against infection, disease and transmission. In fact, an intranasal vaccine could also be used in combination with an intramuscular vaccine to elicit mucosal immunity and serve as a booster for systemic immunity.
We have a precedent. FluMist is a live but weakened influenza vaccine delivered by intranasal spray and this type of mucosal vaccine has been shown to decrease the transmission of influenza to close contacts.
Because of their potential to block transmission, vaccines that stimulate nasal mucosal immunity may be essential to bring the pandemic to an end. However, it will take a little more time to develop and test these newer vaccines as we can’t sacrifice efficacy and safety for speed.
Until then, the public must take precautions to keep this virus under control. Even after vaccination, our best weapon is social distancing, testing and masks. They must remain a core part of our public health strategy even as the first-generation vaccines roll out.