Thursday Update for 2020-12-03: Elephino
Herewith three items of pandemic news you may have missed recently: People who shed virus for months; two online risk estimators; and the ins and outs of taking two different vaccines. Plus the usual frippery.
Taking different vaccines
What happens if you get a first shot of Moderna’s mRNA vaccine and then a booster of Oxford/AstraZeneca’s adenovirus-vectored one? You might as well ask what you get if you cross an elephant with a rhinoceros. The answer: elephino.
Derek Lowe collects what is known, what is suspected, and what is still mysterious about the interactions of disparate vaccines for the same condition. This pandemic is singular in many ways, and one of them is a plethora of vaccines all targeting the same pathogen, built on different technologies and platforms, many of which are likely to be available simultaneously, most of which will require two shots.
Lowe goes through examples from history in which two different vaccines seems to improve the immune response (the oral [Salk] and injectable [Sabin] vaccines against polio); others in which they seem to be interchangeable (various vaccines for hepatitis A and B); and still others in which the order of injections matters (pneumococcal vaccines).
Lowe’s bottom line is: “Overall, though, I would tend to think that it would work out… but… educated guesses will only take you so far.”
Translated: elephino. Be safe, don’t mix and match your vaccines.
Two risk estimators
As the pandemic wears on, and we learn more about the virus’s modes of transmission, more tools are appearing to help us estimate the risks of various situations and actions. Here are two new ones that seem to me particularly detailed and helpful.
The first starts with the assumption that one person in a room with you is infectious. How do the parameters of room specifications, ventilation, and occupant behavior all interact to determine how long you can stay in that room before it’s likely that you will get infected too? This calculator lets you tweak all the knobs with abandon. It was developed by a pair of applied mathematicians at MIT. Here is a Fast Company writeup on the tool.
The second calculator lets you evaluate quantitatively the risk of activities (such as grocery shopping) with respect to a risk “budget” that you choose. Are you willing to assume a risk of 1% per year of contracting Covid-19? That’s 200 microCOVIDs per week according to the calculator. A high-risk person might choose to stay within a budget of 20 microCOVIDs per week. I learned that a shopping trip to Trader Joe’s in Ramsey County, Minnesota might use up 40% of my weekly allotted 200 microCOVIDs. I’m getting groceries delivered for now.
Long-term virus shedding
Some Covid-19 patients who are immunocompromised — those undergoing cancer treatments for example — may remain infectious with SARS-CoV-2 for two months or more. It stands to reason: these people have essentially no immune system to knock the virus down, so it continues proliferating.
A new study published in the New England Journal of Medicine followed 20 patients, 15 of whom were receiving active cancer treatment or chemotherapy and 11 of whom had severe Covid-19. They found one immunosuppressed patient who showed positive on an RT-PCR test (but not shedding infectious virus) after 78 days, and another who was still infectious after 61 days.
The researchers cultured samples from the patients to see whether virus would grow, and performed whole-genome sequencing on the samples to assure that positive patients had not become reinfected. The researchers suggest that isolation guidelines may need to be revised for patients whose immune systems are suppressed. Here is a summary of the research from the Univesity of Minnesota’s CIDRAP.
As a reward for your patience, here is today’s frippery: a recipe for pasta, from a restaurant in Montreal, cooked in two bottles of good red wine. And two sticks of butter. You’re welcome.
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