It should be obvious by now that the adoption of measures to prevent the spread of coronavirus SARS-CoV-2, which causes COVID-19, has become politicized. Consider the presidential campaigns: President Donald Trump held large indoor rallies with mostly mask-less supporters, while President-elect Joe Biden seemed to have a mask sutured to his face and spent much of the campaign in isolation.
Gallup surveys published in November show that partisanship remains the most significant driver of the public’s perceptions of the COVID-19 pandemic and its behaviors in response to it. A majority of Republicans think the best thing for healthy people is to live their lives normally, while most Democrats and independents think sheltering at home is advisable to avoid contracting or spreading the virus. Similarly, Republicans are the most likely to say their lives have somewhat (59%) or completely (8%) gotten back to what they were before COVID-19.
This disparity is unfortunate, because it has never been truer that “we’re all in this together,” or more obvious that we need to rev up our efforts to minimize the probability of spreading COVID-19 infections, if we are “to return to normal activities.” A key metric, the percentage of positive tests for the virus, is currently unacceptably high – the seven-day average is currently over 9%, while the target is to keep it under 3%.
A high percentage of positive tests means there is significant community spread of the virus, which makes effective testing, tracing, and isolation difficult, if not impossible. Moreover, the seven-day average of daily new cases has been increasing sharply over the past six weeks, and is currently approximately 160,000 per day (see figure below). These are ominous signs as we approach the winter months, with people often congregating indoors in poorly ventilated spaces.
There are various interventions that can significantly lower the probability of contracting COVID-19. This is the essence of preventive medicine in general, and epidemiology in particular. For example, many of us take drugs to lower our cholesterol levels or blood pressure to reduce the likelihood of cardiovascular disease. Analogously, there is intense competition to develop a vaccine to prevent COVID-19, which will eventually be a game-changer. But wide availability of a vaccine is many months away.
In all these cases, the strategy is one of managing probability – more specifically, reducing the chances of being exposed to an amount of coronavirus sufficient to penetrate your natural defenses and cause an infection. Thus, the more preventative measures, the better. This is shown nicely in the figure below, which was created and tweeted by Australian virologist Ian Mackay:
I was asked by a friend about the transmissibility of the virus from dog fur – for example, if your dog was petted by a virus-shedding stranger you encountered during a walk. The Center for Disease Control’s thinking as of June 22 was that the probability of that kind of transfer is very low, although a few weeks earlier, its specific advice about pets had been, “Treat pets as you would other human family members – do not let pets interact with people outside the household.”
Those seemingly contradictory statements reflect that the science of viral transmission is all about probabilities. Just as the chance of your being infected by another person is a function of time of exposure, the number of virus particles you encounter, whether there’s dilution (lowering of the concentration of virus particles) from good ventilation and filtration (or wind) – and a few other factors – the same is true of the transfer of viral particles from a pet.
So why the earlier, more risk-averse statement from the CDC? The most likely scenario for transmission would be that person A, who is infected with coronavirus and in the high-shedding stage (just before or just as he becomes symptomatic) breathes, coughs, or sneezes on a dog, and then shortly afterward, person B pets the dog, picks up a significant dose of virus, and then unwittingly touches his face, getting enough virus into his mouth, nose, or eyes to become infected.
In other words, all of those things would have to happen, keeping in mind that the virus is rapidly killed by sunlight and diluted by good ventilation, including wind. (Not to mention that the body’s nonspecific first line of defense, “innate immunity,” can fend off small amounts of pathogens, including coronavirus.) Therefore, although not zero, the probability of becoming infected in such a scenario is surely very low.
As the pandemic continues, we’re learning more about risk and probability of transmission. For instance, an article in the Proceedings of the National Academy of Sciences reported that a few “superspreaders” of coronavirus infections are disproportionately responsible for the spread of disease: Just 2% of infected people were responsible for 20% of transmissions. It may be more accurate, however, to think of this phenomenon as being super-spreading circumstances, rather than persons, because it seems that the time of greatest transmissibility of the virus is during the few days prior to the appearance of symptoms and for a day or two after.
The high transmissibility before symptoms appear is particularly insidious, especially given the recent rise in the upsurge in the number of cases of COVID-19 in the U.S. since mid-October (see top figure above). To be clear, the more cases there are, the more opportunities that exist for people to come into contact with others while they are infectious.
Different behaviors and activities confer different degrees of risk, and the Texas Medical Association has published a useful chart that ranks the risk – i.e., the probability of contracting COVID-19 – from many situations:
Academic and industrial researchers are working feverishly on every imaginable aspect of how to prevent and treat COVID-19 infections, including epidemiology, virology, immunology, pulmonary medicine, and the development of drugs and vaccines. And the work is already bearing fruit. In addition to learning a good deal about transmission of infections, physicians have become much more proficient at managing COVID-19 patients in intensive care units, and the mortality rate has been dropping steadily. Hundreds of drugs are now in various stages of development, 70 vaccine candidates are in clinical trials and two are being evaluated by the Food and Drug Administration for Emergency Use Authorizations, which could come by the end of the year.
COVID-19 vaccines will likely not be widely available until mid-2021, however, so for the foreseeable future, masks, social distancing, frequent hand washing, good ventilation, and some restrictions on businesses will continue to be important – for my fellow Republicans, as well as others.
Henry I. Miller, a physician and molecular biologist, is a senior fellow at the Pacific Research Institute. He was the founding director of the FDA’s Office of Biotechnology. You can find him on Twitter at @henryimiller.