Question: Now that our 64 year old sister is 6 days into her breakthrough infection, we have two different doc opinions on the usefulness of monoclonal antibody treatment for her. ER doc does not think them effective since the fully vaxxed are making their own antibodies. Any data on that?

Answer: Usual disclaimer: I’m not a doctor and you should definitely talk with your doctor about treatment options, which you’ve clearly already done!  The short answer to your question is that monoclonal antibodies could very well help your sister, even though she’s already been vaccinated.  Indeed, infectious disease experts have recommended monoclonal antibody treatment for breakthrough infection and a recently published case report indicates that such treatment was beneficial to an older patient with a breakthrough infection. Based on current evidence, If it were me or my family member, I’d push to receive the treatment.  Related aside: you may also want to think about getting the treatment for yourself as post-exposure prophylaxis. 

Monoclonal antibodies have been shown to reduce the severity of COVID if given early in the course of infection (e.g. given while cases are mild to moderate).  The FDA has granted emergency use authorization for three types of monoclonal antibody treatments:

1. On November 21, 2020, FDA authorized combination treatment of casirivimab and imdevimab (REGEN-COV) to treat mild to moderate COVID and on July 30th, 2021, FDA authorized REGEN-COV to help prevent COVID among people exposed to the virus who are at risk of severe disease.
2. On May 26, 2021, FDA authorized sotrovimab to treat mild to moderate COVID.  Unlike the other two monoclonal treatments listed here, the US federal government is not purchasing sotrovimab.
3. On August 27, 2021, FDA reauthorized the combination treatment of bamlanivimab and etesevimab for use in states with low instances of variants resistant to the combinations (22 states, none of which are in the South or mid-Atlantic).

Given FDA authorization status and federal government purchasing status, REGEN-COV is likely your best bet in terms of accessibility.  The FDA’s REGEN-COV FAQ is online, here.  It is generally given intravenously and injection site reactions are the most commonly reported adverse events.  The only reason I can see for not giving REGEN-COV is concern about adverse events, but as you’ll read in the FAQ, such events seem to be uncommon among patients with mild/moderate disease, though the evidence base is still a bit thin.