Since the COVID-19 vaccines were authorized by the FDA, one of the big questions has been how well they prevent transmission of the COVID-19 even among those who have been vaccinated. The clinical trials used disease — an infection with symptoms — as the endpoint because stopping severe disease and death was the most important priority. In addition, it’s very difficult to develop a vaccine that creates sterilizing immunity, the type of immunity that prevents infection — the virus’s ability to enter cells and begin replicating.
A handful of vaccines can prevent infection, but most only prevent disease. If the COVID-19 vaccines do not prevent infection, that means a person who is vaccinated can theoretically pick up the virus, which will then replicate for a short time before the immune response takes care of it.
During that time, the vaccinated person would potentially be infectious to others, though less so than a symptomatic person since the vaccinated person would not have much virus (viral load) in their body. If, however, the vaccines can prevent infection entirely, then most vaccinated people would not be likely to pick up the virus and risk passing it on to others.
For journalists writing about these vaccination angles, a new data section at the AHCJ Medical Studies and COVID-19 Core Topics includes a list of the studies through April 20 which look at how well the vaccines prevent transmission. The list is not necessarily exhaustive, but it includes the studies I was able to track down so far.
The list includes the following studies (see the Data section for complete citations):
- Moderna mRNA-1273 Sponsor Briefing Document Addendum
- Janssen Ad26.COV2.S Vaccine for the Prevention of COVID-19, pg. 35.
- Initial real world evidence for lower viral load of individuals who have been vaccinated by BNT162b2 (preprint)
- FDA-authorized COVID-19 vaccines are effective per real-world evidence synthesized across a multi-state health system (preprint).
- Effectiveness of BNT162b2 mRNA Vaccine Against Infection and COVID-19 Vaccine Coverage in Healthcare Workers in England, Multicentre Prospective Cohort Study (the SIREN Study) (preprint)
- Early rate reductions of SARS-CoV-2 infection and COVID-19 in BNT162b2 vaccine recipients
- Initial report of decreased SARS-CoV-2 viral load after inoculation with the BNT162b2 vaccine
- Impact of the COVID-19 Vaccine on Asymptomatic Infection Among Patients Undergoing Pre-Procedural COVID-19 Molecular Screening
- SARS-CoV-2 Infection after Vaccination in Health Care Workers in California
- Early Evidence of the Effect of SARS-CoV-2 Vaccine at One Medical Center
- BNT162b2 mRNA Covid-19 Vaccine Effectiveness among Health Care Workers
- BNT162b2 mRNA Covid-19 Vaccine in a Nationwide Mass Vaccination Setting
- Interim Estimates of Vaccine Effectiveness of BNT162b2 and mRNA-1273 COVID-19 Vaccines in Preventing SARS-CoV-2 Infection Among Health Care Personnel, First Responders, and Other Essential and Frontline Workers