Marielle Volz

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Covid-19: My Current Model

In the UK school absences for an unexcused reason (i.e. a vacation during the school year) are fined, so it is more rigid system than in the U.S.

Primary schools have been re-opened here for subset of students last week, and it is not mandatory.

I'd be surprised if you're correct on this, even on average, for the U.S., given that there are so many regional differences from state to state there.

Do 24-hour hand sanitizers actually work?

Update with some more info: has some general information about hand sanitisers and includes info about BZK - they caution that it works less quickly than alcohol based ones, so perhaps that's useful to take into account.

Also, it may interest some people that BZK is the active ingredient in Lysol spray (US) and Dettol spray (UK). (Do not use them as hand sanitiser as they have other ingredients and are not formulated for hands!)

How to fly safely right now?

Pubic hair moderately protects only against those STDs which infect skin cells and are transmitted by skin-to-skin contact: herpes, HPV, molluscum contagiosum.

Respiratory viruses do not infect skin cells and people aren't rubbing their faces together, so there's no plausible method of action here.

Coronavirus is Here

Can you provide a citation for the breakdown of deaths by age? There was at least one confirmed death of a 2 year old in China a month ago. It's certainly negligible, but not 0.

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Is there any value in self-quarantine (from Coronavirus), if you live with other people who aren't taking similar precautions?

That factor is called the secondary attack rate; I've seen values ranging from as low as 10% in one study (which has garnered a lot of scepticism) and in some larger studies, ~ 40%.

Preventing transmission in a shared space is very difficult. I can't give specific estimates as to how much any of the measures you mentioned would reduce that likelihood, unfortunately.

Is there any value in self-quarantine (from Coronavirus), if you live with other people who aren't taking similar precautions?

Thinking about it with a toy model:

Assume you on average contact 25 people a day when you go out, and each of your housemates each also contacts 25 people a day. Also assume if they become ill, you're 100% likely to get it from them. (These are not necessarily realistic assumptions, so please don't infer anything from these particular numbers!)

This means that if you go out, you're effectively contacting 100 people a day (75 of these by proxy.) If you stay home you're reducing your total number of effective contacts from 100 to 75, so a 25% reduction. This is still an overall reduction in your total exposure.

Whether that reduction will be enough for you for it be worthwhile depends a lot on the specific numbers. These numbers include the overall risk of infection per contact (at present likely low but could increase, also depends a lot on where you live), how many contacts you and your housemates actually have, and the probability of getting it from them if they do get infected (probably a lot less than the 100% assumed here).


The virus that causes COVID-19, SARS-CoV-2, is phylogenetically most closely related to SARS-CoV, the virus that causes SARS- this is why taxonomists named it SARS-CoV-2.

However, you shouldn't and can't expect SARS-CoV and SARS-CoV-2 to have a more similar course because of this, as compared to MERS-CoV- and in fact thus far they've behaved differently. For instance, the death rate for COVID-19 is considerably lower than for SARS. Paradoxically, this may be responsible for its greater spread, because people who are less severely ill or asymptomatic are much more able to spread disease widely or in an undetected fashion. In the US there has been undetected community spread of SARS-CoV-2.

I don't think it's useful to use epidemiological properties of other related strains at present; the data we have directly about SARS-CoV-2 is already superior to extrapolating this way. COVID-19 has already expanded far more geographically than SARS ever did, which already makes the overall probability of extinction of it less likely than with SARS, as generally speaking extinction probability decreases with increasing population size.

Do 24-hour hand sanitizers actually work?

A brief Google suggests BZK is effective against SARS-Cov-2 on surfaces. There is no research on it on hands that I found specifically for coronaviruses. Hands are generally more difficult to disinfect. (About SARS-CoV, but similar enough virology that it probably applies)

I'd be most skeptical of the claim it is effective for 24 hours on hands, so if you did get it, I would re-apply whenever you would normally use alcohol-based sanitiser and not rely on this claim.

This paper suggests BZK is more persistent on hands than alcohol based sanitiser for a bacterium (MRSA), which makes sense a priori, but only up to 4 hours.