With intramuscular vaccination there are two types of "breakthrough". There is the real breakthrough where internal body organs have extensive viral replication

With intramuscular vaccination there are two types of "breakthrough". There is the real breakthrough where internal body organs have extensive viral replication. Then there's infection of the surface tissues of the tubes that run through our bodies. Intramuscular vaccination provides long lasting antibodies to the body proper and these seep into the lungs surface tissues too. But there's no long term antibodies (or resident B or T cells) in the upper respiratory mucosa (throat/nose/sinuses). That means even if you're doubly vaccinated + 2 weeks your nose/sinuses (where they test for virus) can be infected and shed virus. But just because you test positive in the upper respiratory mucosa does not mean your internal organs will be infected. This shows clearly in hospitalization vs. confirmed infection cases in the vaccinated. So... there's breakthrough... and there's BREAKTHROUGH. Studies, and news reporting, really need to begin presenting a more nuanced message about these numbers. And more importantly we need intranasal vaccine boosters to follow intramuscular to end the pandemic. https://science.sciencemag.org/content/373/6553/397 https://science.sciencemag.org/content/373/6553/397 "the ideal vaccination strategy may use an intramuscular vaccine to elicit a long-lived systemic IgG response and a broad repertoire of central memory B and T cells, followed by an intranasal booster that recruits memory B and T cells to the nasal passages and further guides their differentiation toward mucosal protection, including IgA secretion and tissue-resident memory cells in the respiratory tract." https://www.gov.uk/government/publications/long-term-evolution-of-sars-cov-2-26-july-2021 https://www.gov.uk/government/publications/long-term-evoluti... page 5, #8. "Whilst we feel that current vaccines are excellent for reducing the risk of hospital admission and disease, we propose that research be focused on vaccines that also induce high and durable levels of mucosal immunity in order to reduce infection of and transmission from vaccinated individuals. This could also reduce the possibility of variant selection in vaccinated individuals."