Can we still catch and spread COVID-19 even if we are vaccinated?
We can probably be infected with COVID-19 because we currently have a series of vaccines available that trigger an internal response. So, even if someone is protected against the disease, there is a possibility that they could replicate the virus in their nostrils or respiratory tract and become contagious. This is why we need to continue wearing a face mask, until we have more data.
In terms of immunity, we could say that we have different compartments. The most important of all is our respiratory tract, which is the gateway for all viruses and has a kind of police force of its own that watches out for any pathogen that might attack us. Because this is a local area, we can refer to it as the local police, the one making sure that no one enters. Then we could talk about a separate compartment, our entire internal system. Imagine it has a national police force that makes sure that, should any pathogen enter, it is examined, detected, and trapped, and immunity is then generated.
When we are injected with an intramuscular vaccine, like the ones we have right now against coronavirus, the response that we generate is internal, because what we are actually receiving, whether it is pathogen fractions or RNA, generates a response in that internal area. So both T-lymphocytes and B-lymphocytes are going to generate an internal response. The fact that the vaccine is not administered through the respiratory tract means that the local mucosa obviously does not have that memory generated by the internal system. That is why, when the virus comes into contact with the mucosa, a vaccinated person might be able to generate an immune response while the virus is still replicating, until the local police can trap and block the virus. At the moment we have no data, because the vaccination effort has just started, and we do not know to what extent our internal protection will be able to help the local police to block the virus.
Among the vaccines that are being developed against COVID, we have a wide arsenal of different strategies, both traditional and novel. Within this spectrum, there are not only intramuscular vaccines, but also some inhaled ones. The advantage of an inhaled vaccine is that, because it is administered through the nose, when it is applied, it first generates a local response, generating antibodies in the form of secretory immunoglobulin A, produced in the mucous membranes. But at the same time, our internal system – this national police – would also be able to generate an immune response both in the form of antibodies, generated by plasma cells, and an immunological memory through T-lymphocytes immunity. This vaccination strategy has the advantage of sterilising the respiratory tract.
The health passport is a measure to address the economic impact of the pandemic, and the effort to generate documentation is certainly understandable. But the starting point is that we do not know to what extent this vaccine is sterilising, so a health passport would only make the statement that the individual is protected; it would not be imply that they are not contagious.
Answered by Maria Garcés-Sánchez, specialist in paediatrics and researcher in the Vaccines Area at FISABIO.
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