Airborne transmission

Air Filtration/UV Light Can Remove Airborne SARS-CoV-2 From Hospital Wards, Study Finds

In a study published earlier this year, Paul McKeigue and colleagues analysed data on all diagnosed cases of COVID-19 in Scotland, as well as a large number of matched controls. They found that a staggering 30% of severe cases (those that resulted in critical care admission or death) were linked to a recent hospital visit.

This suggests widespread nosocomial transmission of SARS-CoV-2. In other words, a lot of people caught their infections in hospital, and then became seriously ill.

The fact that such a large portion of severe cases were linked to a recent hospital visit is actually not so surprising. After all, people vulnerable to COVID-19 (the elderly and persons with underlying health conditions) are overrepresented among those who make frequent hospital visits.

Nonetheless, it’s rather concerning that hospitals – places where people are meant to come out healthier than they go in – were a major site of SARS-CoV-2 transmission.  

Given that COVID-19 patients, as well as those vulnerable to COVID-19, tend to be concentrated in hospitals, making efforts to reduce nosocomial transmission would seem like a top priority. Indeed, one would expect interventions that did reduce such transmission to have a large benefit/cost ratio.

Which makes a new preprint so interesting. Andrew Conway-Morris and colleagues investigated whether airborne SARS-CoV-2 could be removed from hospital wards using portable devices that filter and sterilise the air.

Their experiment involved two units within an English hospital: an ordinary Covid ward, and an ICU containing Covid patients. The presence of airborne SARS-CoV-2 was measured during three consecutive weeks: one in which the devices were turned off; one in which they were turned on; and one in which they were turned off again.

In addition to measuring the presence of SARS-CoV-2, the researchers measured the presence of various other microbial bioaerosols, such as E. coli and staphylococcus. Their results for the Covid ward are shown in the figure below.

When the devices were turned off, many microbial bioaerosols (including SARS-CoV-2) were detected. Yet when they were turned on, all of these except candida were undetectable. This means the devices were successful in removing not only SARS-CoV-2, but also other potentially dangerous pathogens.

As the authors note, SARS-CoV-2 was detected on “all five days before activation of air/UV filtration, but on none of the five days when the air/UV filter was operational”. The virus was again detected on “four out of five days when the filter was off”.

Interestingly, SARS-CoV-2 was barely detected in the ICU (regardless of whether the devices were turned on). This may be because viral shedding is lower among critically ill patients, or because ICU staff were wearing proper N95 masks.

It’s important to note: the study didn’t show that the devices actually prevent transmission of SARS-CoV-2 in hospitals. However, the results constitute strong circumstantial evidence that they would reduce transmission.

While attempting to halt transmission of SARS-CoV-2 in the community at large is costly at best and futile at worst, attempting to do so in high-risk hospital environments makes a great deal of sense. Further investigation into the efficacy of these devices is clearly warranted.  

Another Study Claims to Show Masks Work Against Covid – But Does No Such Thing

A new study has appeared claiming that cloth masks work to reduce the spread of COVID-19 – provided they’re made of three layers of cotton. The Mail reports on its findings.

Researchers at the Indian Institute of Science used synthetic cough droplets to model how well different mask types stand up to coronavirus particles.

They found that surgical and N95 masks are still the most effective at stopping coronavirus spread.

Cloth masks may be a suitable alternative if these masks only if they have at least three layers and are made of cotton, the team found.

These findings may be particularly useful for lower-income countries like India, where surgical masks are not easily accessible to the general population.

In fact, though, the study has not shown anything about the effectiveness of cloth masks to prevent infection. It is not a study of real-world transmission at all but a laboratory test of how masks stop synthetic droplets. These droplets are around 500 micrometres in diameter, so not aerosols, which are typically considered to be much smaller (certainly less than 100 micrometres and possibly less than five). It therefore hasn’t even considered how well the masks impede aerosol transmission, which is one of the main modes of transmission.

A recent study, the Bangladesh mask study, did look at the real-world effectiveness of cloth masks. It found a slight reduction from 0.76% antibody prevalence in control villages (no masks) to 0.74% prevalence in cloth mask villages, though this was not statistically significant. There were numerous problems with this study, not least than it was confounded by additional interventions (an awareness campaign) and did not properly measure initial antibody and prior infection levels. However, even with these limitations it still indicates very little discernible difference.

The Danish mask study, Danmask-19, found no statistically significant effect on infection from wearing surgical masks either. This is in line with pre-Covid evidence on the lack of effectiveness of masks in protecting from respiratory infection and transmission.

When will the mask zealots admit that their pet intervention is a dud?

What SAGE Gets Wrong: The Evidence that Almost Everyone is Exposed During a Surge and Most Are Immune

During a Covid surge, what proportion of the population is exposed to an infective dose of the virus, which they either fight off with no or minimal symptoms or are infected by? This is one of the most important questions scientists need to answer.

It’s closely related to the question of whether lockdowns work. If lockdowns work then, as per SAGE and Imperial orthodoxy, the restrictions successfully prevent the virus from reaching most people, who remain unexposed and susceptible – and hence in need of vaccination to protect them when the protective restrictions are lifted. If lockdowns don’t work, however, then they don’t prevent the virus spreading, and thus the majority of people will be exposed to it as it spreads around unimpeded by ineffectual restrictions.

Another related question is: What proportion of exposed people are infected? Using ONS data we can estimate that around 10-15% of the country tested positive for SARS-CoV-2 over the autumn and winter. How many were exposed to the virus to produce this number of infections? Was it, say, 10-20%, with half to all of them catching the virus? Or was it more like 80-90%, with around 10% being infected? It’s a question that makes all the difference in our understanding of the virus and how to respond to it.

If almost all are exposed during a surge, and relatively few of them are infected, then a number of things follow. First, most people have enough immunity to fight off the virus when exposed to it, and only a small minority become infected. Second, the surge ends when enough of that small minority who are particularly susceptible to this virus or variant acquire immunity through infection, i.e., when herd immunity is reached. Third, there won’t be another surge or wave until there is a new virus or variant which evades enough of the existing population immunity to require herd immunity to be topped up via a further spread of infections.

If, on the other hand, very few are exposed during a surge, and most of them are infected, none of these things is true. It means: Most people have little immunity and are highly susceptible. A surge which infects 10-20% of the population has exposed not much more than that. The surge does not end because of herd immunity but because of restrictions. And there will be another surge as soon as restrictions are eased or behaviour changes and the unexposed begin to be exposed again. SAGE orthodoxy, in other words.

The evidence, however, is strongly supportive of the first position – ubiquitous exposure – not the second, limited exposure.