One possible indirect benefit of a COVID vaccine, then, may be to reduce the viral load in so-called breakthrough cases, or vaccinated people who get infected.īecause many health care workers are now routinely tested for COVID, regardless of whether they have symptoms, much of the early real-world data on vaccine effectiveness in blocking infection has come from this population. If a carrier’s viral load is relatively low-meaning that fewer viral particles are shed while breathing and speaking-the risk of transmission is substantially reduced.
Not every carrier spreads the virus, though. But the trials provide little or no data on whether the vaccines can entirely block infection, which is the surest way of minimizing spread of the virus.Ĭonsidering that at least one third of COVID infections are entirely symptom-free, yet still potentially contagious, it is important to know whether vaccinated people are likely to become carriers of the virus. These are the efficacy numbers in the headlines-as high as a 95 percent reduction in symptomatic COVID cases for the two FDA-authorized mRNA-based vaccines. Vaccine trials are typically designed to determine whether an immunization prevents people from getting sick. These findings have important implications for how quickly we can get the pandemic under control, and for what we say to those who are hesitant about getting vaccinated. In recent months, there has been a deluge of data on the risk of transmission after vaccination. Such silent spread could complicate efforts to control the pandemic. However, there has been uncertainty about whether vaccinated people who still get infected-perhaps with very mild symptoms, or none at all-might pass on the virus to others. COVID vaccines have proved to be magnificent successes, dramatically decreasing the number of cases, hospitalizations and deaths.
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