We are facing our toughest challenge of the pandemic to date. Dr Siouxsie Wiles explains why and what that means for how we need to respond.
The virus has changed
One of the reasons we are in the situation we are in now is because countries that could and should have done things differently didn’t. Widespread community transmission has enabled variants like delta to evolve. With many countries now entering a new wave of infections the virus will keep evolving. We don’t know what this means for us in the future, but one thing is clear: the virus we are currently dealing with is not the same one we faced at the beginning of the pandemic, nor even during our last serious outbreak in August 2020.
I’ve written before about how much more infectious delta is but a new study just published in The Lancet Infectious Diseases has shown it’s more dangerous too. Researchers followed 43,338 people who tested positive for Covid-19 in England between March 29 and May 23 this year, and whose viral sample they were able to sequence. That allowed them to look at the outcomes for people who were infected with the already more infectious alpha (B.1.1.7) variant of the SARS-CoV-2 variant which was dominant at the time, and the delta variant which had recently arrived. What the researchers were interested in was whether the delta variant was causing more severe illness than the alpha variant.
A previous study of 829 patients in Singapore showed that after adjusting for age and sex, the delta variant was associated with higher odds of a patient needing oxygen, being admitted to ICU, or dying. Would the same be true in England? All in all, the researchers ended up with data on 34,656 people with the alpha variant and 8,682 people with the delta variant. And yes, their data paints a similar picture. It’s hard to compare the two studies directly because they present the data differently, but the study from England calculates that after adjusting for age and other factors, the delta variant causes more than twice as many people to be hospitalised within two weeks of testing positive compared to the alpha variant. That was true whether people were unvaccinated or had received one dose of vaccine. Given this is data from England, that likely means one dose of the AstraZeneca vaccine which the data suggests is less protective than Pfizer, especially after just one dose.
If we look at how people are already hospitalised at this stage in our current outbreak, not surprisingly, delta is behaving the same way in New Zealand too.
Airborne transmission means we need to change how we operate
Covid-19 spreads from person to person and it starts to do that before people even know they are infected. But we were initially wrong about how the virus does this. Yes, droplets are one way it can spread when people are in very close contact. But it’s mainly airborne. For those of you who are interested, a really extensive review of the subject has just been published in the journal Science. It explains how our understanding has been hampered by assumptions and historical definitions, and how a growing body of evidence is changing everything we know about how infectious microbes can and do spread through the air.
Here’s the take home message from the review. Yes, infectious people do produce droplets through coughing or sneezing and these can infect people at distances less than half a metre. But when we breath, talk, sing, shout, cough, and sneeze we release aerosols that are small enough to linger in the air. These aerosols linger in the air and accumulate in confined and poorly ventilated spaces. And that means they can spread the virus from close range as well as when people are further away. That means relying on staying two metres away from other people indoors is not good protection from Covid-19.
Unfortunately, many of the protections we put in place at the beginning of the pandemic were to protect against droplet transmission. Some of them may work a little for Covid-19, but others will likely just lull us into a false sense of security. So, what will work for Covid-19? Let’s start with an easy one. Masks. As we’ve been saying from the beginning of the pandemic, not all masks are created equal. But the studies are clear that almost all masks will offer some protection. My one plea is that you don’t wear a mask with a valve. If you have Covid-19, that’ll just release more virus into the air around you. Which defeats the point of us all wearing a mask.
The type of mask you should wear really depends on your risk of getting Covid-19. N95 are the best at protecting people from the virus so they should be reserved for those most at risk of being infected. In my opinion, that’s those dealing with infectious or potentially infectious people at our borders, in our managed isolation and quarantine facilities, and in our healthcare system. At alert level four, it’s also our essential workers. We cannot afford to have them coming down with or transmitting Covid-19 in their workplaces.
The other big thing that will change the risk of infection is paying more attention to shared air, especially indoors. This means thinking more about airflow, ventilation, and filtration. The greater airflow we get outdoors disperses aerosols quickly. But indoors, the airflow is restricted by barriers like walls and ceilings. Improving airflow can be as simple as opening windows and doors or by using mechanical blowers. The WHO has recently recommended a ventilation rate of 10 litres per second per person. Airflow patterns are important too, though, as inappropriate ventilation can create hotspots where risk of infection is increased rather than decreased. Lastly, indoor spaces can also be improved using things like high-efficiency particulate air (aka HEPA) filters which are really good at removing virus-laden aerosols.
Here’s another important point raised by the review though. Using barriers designed to block droplet spray from coughs and sneezes – like the plexiglass barriers that have turned up everywhere – can actually mess with airflows and potentially even trap higher concentrations of aerosols exactly where we don’t want them.
Tightening alert level restrictions
Our goal with using the alert levels is to limit the number of people who are in contact with each other in order to stop the virus transmitting. Bringing the effective R number of the outbreak below one means the outbreak will die out. The closer that number is to one, the longer it will take. Doing everything we can to get that number closer to zero will mean the outbreak is over more quickly.
To bring the effective R number down we may need to need to tighten our alert level restrictions. Let me be really clear: we don’t need an alert level five. We certainly don’t need curfews or limits on the amount of time people can be outdoors. Rather we need to tighten up the places where transmission happens. And that’s mainly at essential workplaces. (I plan on addressing transmission in schools at a later date).
The first big thing we have to do is ensure that anyone who can work remotely is working from home. Even if they are classed as an essential worker. I’m gutted to see that some opposition MPs have decided that parliament must meet in person at alert levels three and four. That puts not just them at risk, but everyone who needs to now come to the Beehive so that they can work there. Whatever your politics, I don’t think this is showing good leadership during a pandemic and sets a dangerous precedent. It wouldn’t surprise me if people begin to take that as a sign that they too can travel around the country and/or go in to work. All at a time when we need our restrictions to be as tight as possible.
The definition of essential workplaces also seems to have changed a little this time around. I know that every business is important not just to the economy but to its owners and employees. But if they aren’t really essential, then they may well just be adding to the number of workplaces operating and increasing the number of people who are in contact with each other. Again, just because people can stay two metres away from each other, doesn’t mean Covid-19 wouldn’t tear through the place if given half a chance. Each workplace that is open connects the bubbles of all its employees. You only have to look at our case numbers to see why we need to keep that number to a minimum.
The more we can limit transmission of the virus, the lower we can keep the effective R number, and the quicker the outbreak will be brought under control. That will save lives and get us back to enjoying all the benefits of living at alert level one.
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