Prior to the recent protests, the US seemed to be making some progress on controlling coronavirus, with an r0 of probably around 0.9, a slowly declining number of cases, and many states starting to ease lockdown. In particular, restrictions on large gatherings helped significantly slow the spread, because they reduce both the number of infected people who can spread it and the number of new people who can become infected. One (BERI funded!) study suggested that banning large gatherings reduced r0 by around 28%.
Unfortunately, protests seem in many ways ideal for spreading the disease. They involve a large number of people in a relatively small area for an extended period of time. Even protests which were advertised as being socially distanced often do not end up that way. While many people wear masks, photos of protests make clear that many do not, and those that are are often using cloth masks that are significantly less effective than surgical or n95s in the face of repeated exposure. Additionally, protests often involve people shouting or chanting, which cause infectious droplets to be released from people's mouths. Exposure to tear gas can apparently also increase susceptibility, as well as cramped indoor conditions for those arrested.
It's hard to estimate how many new cases will be caused by the protests, because there doesn’t seem to be good statistics on the number of people at protests, so we can't model the physical dynamics easily. A simple method would be to assume we have lost the benefits of the ban on large gatherings over the last week or so. On the one hand, this may be an over-estimate, because fortunately most people continue to socially distance, and protests take place mainly outside. On the other hand, protesters are actively seeking out (encouraging others to seek out) boisterous large gatherings in a way they were not pre-March, which could make things even worse. On net I suspect it may under-estimate the incremental spread, but given the paucity of other statistics we will use it as our central scenario.
If the r0 was around 0.9 before, this suggests the protests might have temporarily increased it to around 1.25, and hopefully it will quickly return to 0.9 after the protests end. Even if we assume no chain infections during the protest - so no-one who has been infected at a protest goes on to infect another protester - this means the next step in disease prevalence would be a 25% increase instead of a 10% decrease. Unfortunately the exponential nature of infection means this will have a large impact. If you assume around 1% of the US was infected previously, had we stayed on the previous r0=0.9 we would end up with around 9% more of the population infected from here on before the disease was fully suppressed. In contrast, with this one-time step-up in r0, we will see around 12.5% of the population infected from here - an additional 3.5% of the population.
Assuming an IFR of around 0.66%, that's a change from around 190,000 deaths to more like 265,000. Protesters skew younger than average, suggesting that this IFR may be an over-estimate, but on the other hand, they are also disproportionately African American, who seem to be more susceptible to the disease, and the people they go on to infect will include older people.
So it seems quite plausible to me that the protests might cause around 75,000 thousand additional Americans to die of covid, including probably over 10,000 African Americans. Additionally, despite the massive reduction in international travel, there will probably be some spread to other countries, especially if they have copy-cat protests.
There is clearly a lot of uncertainty about this number - my guess is that the actual r0 impact may be higher and longer lasting, but the IFR may be lower. If r0 is sufficiently low the disease will be suppressed more quickly afterwards, potentially making these numbers significantly too high (if the r0 were as low as 0.7, the protests would only cause an incremental 20,000 deaths). If r0 is a little higher then these numbers will be a substantial under-estimate. On the other hand, if the r0 was sufficiently high then containment will inevitably fail, and almost everyone in the US will catch it regardless of protests!
However, it seems hard to avoid the conclusion that the incremental number of deaths is quite likely many thousands. (In contrast, the Washington Post estimated that US police killed 41 unarmed people in 2019, of which 10 were black.)
My guess is that the indirect and statistical nature of these deaths makes people less sensitive to them. Probably if they were more emotionally salient, many protesters would not be willing to so endanger their lives.
As a result it seems to me that, even ignoring injuries and fatalities directly incurred during the protests, and the damage caused by associated looting, that the protests are quite bad, and it would be good if instead people stayed home to save lives and protect their local health systems.
I have not edited any of the prior sections
So how close were the predictions in this post? It's very hard to judge, because the main predictions were about the delta between protests and no protests, rather than an absolute forecast. But we can say a few things based on what has happened since the 3rd of June.
I modelled US cases as basically on a declining trend ( r0=0.9 ), which would then see a short one-time increase in r0 to 1.25, and then return to a decline with r0=0.9 . Overall the US numbers would remain on an exponential decline with a one-time step up from the protests.
What actually happened? At time of publication, the 7-day average of daily new cases was 22,000. A month later it had risen to 60,000, and would continue to rise until peaking at almost 70,000 in July. This is a much larger increase in cases than I was expecting, and it coincided almost exactly with the start of the protests.
How much of this was a direct result of the protests? Unfortunately this is hard to tell. My best guess is 'some but not most'.
At the same time as the protests a lot of states were undoing their lockdowns - in my opinion prematurely - which would naturally cause an increase in disease transmission. It is possible that protests increased this effect, by undermining the credibility of pro-lockdown experts for reasons I outlines here. In some cases the government's support for these protests forced them to relax other covid restrictions, as they were found guilty of discriminating in favour of the protests. However I suspect a significant degree of liberalisation would have occurred even without the protests.
One strong piece of evidence would be contract tracing; unfortunately in some cases contract tracers were told by pro-protest politicians not to ask people if they had been to a protest. Public health officials from some cities said that protests caused covid spread; officials from other cities deny it.
The average age of infected people has fallen significantly. This is the age profile for people who go to protests, but also the profile for those who go to bars and clubs. It has also significantly reduced the realised IFR.
A NBER paper from Dave et. al. argues that places with protests saw large offsetting reductions in social activity: the more people protesting/rioting, the less other people wanted to go outside. I didn't consider this sort of behavioural response in the article. To the extent it is true, it means that while protesters did impose costs on others, these costs were borne in the form of more time staying indoors rather than covid transmission.
This study uses newly collected data on protests in 315 of the largest U.S. cities to estimate the impacts of mass protests on social distancing, COVID-19 case growth, and COVID-19-related deaths. Event-study analyses provide strong evidence that net stay-at-home behavior increased following protest onset, consistent with the hypothesis that non-protesters’ behavior was substantially affected by urban protests. This effect was not fully explained by the imposition of city curfews. Estimated effects were generally larger for persistent protests and those accompanied by media reports of violence.