COVID-19: a Quantitative Approach

In a piece at The Hill physician and epidemiologist Dorry Segev advocates a more quantitative approach to dealing with COVID-19:

Instead of just guessing, or assuming “one size fits all” (we saw what a disaster it caused when we assumed immunocompromised patients had the same response as everyone else), we can now test antibody levels and recommend boosters when levels fall below some threshold. We can even choose different thresholds for people of different risk profiles: If you have a higher risk of exposure to SARS-CoV-2 (or exposing others) because of your job, or if you have a higher risk of getting very sick with COVID-19 because of your comorbidity profile, you should get boosted at a higher antibody level. B if you have minimal exposure and are otherwise quite healthy, you could wait to reach a lower antibody level before boosting. This individualized approach would optimize protection while making the best use of available vaccine doses.

Antibody testing can also help us address the major controversy over natural immunity and “vaccine passports.” Many venues, including theaters and concerts and festivals, are starting to require proof of vaccination for entry. Unfortunately, this is quite a blunt instrument for determining how safe someone is to be around others, and it is becoming more and more unreliable as antibody levels from initial “full” vaccination are waning. Ideally, a space is safer if everyone in the space is immune: The risk of someone bringing the virus to the space is minimized, and the risk that the virus would impact the other immune folks in the space is also minimized.

So why have “immunity passports” devolved to “vaccine passports”? For a while, checking vaccination was much easier than somehow determining that someone had enough natural immunity to be safe: In the large clinical trials, nearly everyone mounted a strong antibody response to vaccination, so asking to see someone’s vaccine card was as close to a guarantee as we get these days that the person was immune. However, we are almost a year into vaccines, and antibody levels wane. Today, even vaccination does not necessarily mean strong immunity, and someone who had documented COVID-19 three months ago is likely more immune that someone who was vaccinated a year ago. The way to determine this is to check antibody levels: At a given antibody level, no matter how you got there (vaccines with or without boosters, natural infection with or without vaccines), it is safe for you to be around others.

It makes sense to me. However, nothing will be perfect and nothing will be risk-free. What’s the objective?