The best way to catch COVID-19

A year ago, to the question of, “what is the best way to catch COVID-19?” the only sensible answer was “Not to.” In 2021 and beyond, while that might still be appealing, it is becoming less and less realistic… and in a year or so, it may not be an option at all.

“Just a moment,” I hear you say, “I’ve avoided it so far — why can’t I just can’t go on avoiding it?” In short, because the virus has got better at spreading itself by more than we have improved at controlling its transmission… and you haven’t really avoided it — it’s mainly avoided you. Just over a year ago, I posted this story on the ways in which public health measures are undermined by the prevalence of insecure work. What I wrote in that story about the apparent intractability of Melbourne’s outbreak then, applies equally to the current outbreak in Sydney.

The problem is, NSW has — for a couple of weeks now — brought to bear virtually all of the effective portions of last year’s long (oh god… so very, very long) lockdown in Victoria, and they went into the outbreak with a far superior contact tracing system, but they are still only achieving a “flatten the curve” outcome. This is because the R0 for the delta variant now dominating cases around the world is considerably higher than that of the strains of virus in circulation last year (estimates are rough, given the confounding effects of ongoing control measures and vaccination, but it looks like it is about three times as infectious, with an R0 in the range of 5 to 9, compared with an R0 for the original strain of around 2 to 3).

It’s now looking pretty clear that the only way to achieve full suppression of an outbreak of delta is to (1) lock down immediately when any community transmission is detected, and (2) aggressively contact trace and isolate with world-leading capability, and (3) get lucky. The combination of all three cannot be relied upon to continue. That means eventually this variant is likely to escape all efforts to eliminate community transmission, even if that remains the goal of public health policy. And that means that at some point — I would guess within the next year or two (although modelling the probability is well beyond my capabilities) — you’re going to be exposed to an infective dose of SARS-CoV-2.

So what’s the title about? Naturally, if your objective is just to catch COVID-19, sitting for hours in a room with someone early in their symptomatic stage of illness will probably do the trick. But that’s not really what I’m talking about here — I really mean to ask, given the choice, what are the best circumstances under which to be exposed to SARS-CoV-2?

The answer is a combination of as many as possible of the following:

1. After being fully vaccinated (with any approved SARS-CoV-2 vaccine)
2. At as young an age as possible
3. Where good quality health care and treatment options are readily available, should you need them.

Many of you already will have spotted the contradictions here — and of course, the limited number of variables within any individual’s capacity to influence.

In a few dozen countries, good vaccines are already readily available to everyone, whereas in the majority of countries availability is still limited. If you are lucky enough to have an approved vaccine available to you where you live, but have not yet had your first dose, please go and get it done immediately. Now. Now now. You can read the rest of this story in the waiting room, during the 15 minutes they’ll require you to stay for observation after getting the injection.

The implication of the second one is straightforward: once you can meet the other two conditions, it’s actually better to be exposed to an infective dose of SARS-CoV-2 sooner rather than later. But in order to meet the third condition, you don’t want to catch it as part of an out-of-control outbreak involving lots of unvaccinated people — which would be the most likely scenario to catch it sooner rather than later — because if you are in a situation where there is uncontrolled spread through a significant unvaccinated portion of the population, then you can also expect health services to be overwhelmed, just like in the real-life horror stories of 2020 and early 2021.

I’ve already written about the general path we’re likely to see out of the current approach to handling the pandemic in Australia. There is little doubt — except among plague enthusiasts — that the current approach of aggressively suppressing community transmission achieves the best outcomes for both public health and the economy (because people are what make the economy work… who knew?). But once everyone has been given ample opportunity to be fully vaccinated, we are likely to see policy shifts that result in significant and ongoing community transmission.

Imagine this: it is March of 2022, and every Australian has been able to be fully vaccinated (including the applicable waiting period between first and second doses) since the end of 2021. 80 percent of the population has received at least one dose, with 75 percent fully vaccinated, and vaccination numbers are plateauing.

Then imagine there is an outbreak of cases (the delta variant, again) stemming from an unvaccinated limo driver in Sydney who caught it from international flight crew. Is it realistic to expect that the NSW government would call for another lockdown? That Victoria would lock out all travellers from NSW?

I don’t believe such actions will be politically viable at that point: the people not vaccinated will almost (unfortunately, this is a big almost) all be proud “vaccine skeptics”, and many will be denizens of Facebook groups full of conspiracy theories. It’s a whole lot easier politically to say “we have to lock down millions of people to save the health and lives of the vulnerable in our community” than it is to say “we have to lock down millions of people to save the life of your paleo dickhead co-worker who posts shitty memes on Facebook”.

“Wait a minute — what about herd immunity?” Many of us are familiar with the general idea of herd immunity… and it is indeed a beautiful thing, when it can be achieved. It protects immune-compromised people (see “big almost”, above) and those who are unable (as well as those who are merely unwilling) to be vaccinated. This is made possible with many vaccine-preventable diseases, because the vaccines in question provide “sterilising immunity”, which is to say that vaccinated people are not infected at all even when exposed to the pathogen.

Unfortunately, SARS-CoV-2 is a tricky bastard virus, and given that it appears to have reached something approaching “peak fitness” in the delta variant, herd immunity is likely impossible to achieve. The vaccines are excellent — better than many experts thought possible — providing very high levels of protection against symptomatic illness, and extremely high levels of protection against severe disease (including hospitalisation and death). But they only provide moderate protection against infection. So even the vaccinated can — in a significant minority of cases — still be infected and pass that infection on to others (although experiencing only minor symptoms, if any, themselves).

So we can expect SARS-CoV-2 to continue to move through the population, with unvaccinated people serving as major spreaders (and the overwhelming majority of casualties), but with occasional spread through vaccinated people providing sufficient transmission chains between the unvaccinated. Contact tracing and quarantine/isolation protocols should keep massive outbreaks to a minimum — and that will be needed (pretty much indefinitely) to keep health services from being overwhelmed — but a background murmur of cases everywhere will probably become the new norm.

Another way in which “as young as possible” and “best possible health care and treatment” may come into conflict, is that medical research and health professionals worldwide are continuing to work on new and improving treatments for COVID-19. So although the risk of developing more severe disease increases exponentially with age (even among vaccinated people, albeit from a vastly lower baseline), it might be that someone is still better off getting COVID-19 in a year or two than that same person would be if they caught it now, because more effective treatments will be available to them.

And of course, there is the direct contradiction between “when fully vaccinated” and “as young as possible”, because at the moment there are no vaccines yet approved for children under 12 years of age. However, mRNA vaccines in the US are already in trials among children as young as 2 years old (and there’s no reason to believe that mRNA vaccines will not be safe and effective in young children), so that is not likely to be a problem for very much longer.

I predict that the inability to vaccinate children is likely to be the last remaining anchor for Australia’s aggressive suppression/elimination strategy: no politician is going to want a bunch of pictures of sick children in hospital being put up alongside the picture of them declaring that it’s time to open up “no matter what”.

There is a lot left to play out in this pandemic: as of today, about 200 million people worldwide have been confirmed as infected with SARS-CoV-2. Out of 7.9 billion. 2.2 billion people have been at least partially vaccinated. That still leaves the majority of the world — about 5.5 billion people — immunologically naïve to the virus. Even if we assume that there is drastic undercounting of infections (as is almost certainly the case in parts of the world), it’s not plausible to think that people already infected/recovered would number in the plural billions. Assuming the global rate of vaccination remains steady, we’re looking at another 12 to 18 months before a majority of the global population will have been vaccinated. So the next year or so will continue to resemble the past year or so, much more than it will the pre-pandemic era.

However, our way of thinking about the pandemic is going to evolve much more quickly. This will be especially true in Australia, which has been an exceptional (not always exceptionally good, but always exceptional) place to ride out the pandemic so far. The most important choice any individual can make, is to get themselves vaccinated as soon as possible (with whatever approved vaccine is available). Beyond that, whether or not we engage with them, there will be increasingly broad conversations about how and when to make the policy shift from aggressive suppression of a pandemic disease to which everyone is vulnerable, to ongoing management of an endemic disease to which most people who remain vulnerable do so only by choice.

Coda

There is a chance I’m wrong in the prediction which underlies the above, because I assume that it will never become a winning political tactic to regress to earlier elimination strategies once management of endemic disease with vaccination and good quality treatment is feasible. However, a regression path is still possible.

While the R0 for the delta variant is about 3 times higher than the original strain (hence the near-impossibility of containing outbreaks once they get out of hand), the partial sterilising effect of vaccination reduces the probability of a vaccinated person passing on the virus by about 60–70%… which means that the effective R0 for the delta variant in a mostly vaccinated population, becomes comparable to the R0 for the original strain in an unvaccinated population. We know from extensive experience of that baseline that good-quality contact tracing, combined with occasional not-too-protracted lockdowns for significant outbreaks, is entirely capable of driving community transmission all the way back down to zero.

I don’t think it will happen that way. When the overwhelming majority of the population won’t have anything much worse than minor cold symptoms to fear even if they do get infected, continuing to pursue elimination will be far too politically costly.