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As we are seeing the beginning of the end of the first wave of COVID-19, the burning question is – will there be a second wave? No one knows, and there are both reasons for hope and caution. One sobering fact – the last 14 flu pandemics all had a second wave or multiple waves. SARS-CoV-2 is not the flu, but it is a respiratory virus and spread may be similar. This may also be a function of the dynamics of pandemics more than the characteristics of a specific virus.

A 2013 study modeling the most recent flu pandemics also found they all had at least a second wave. However their models also found that if measures were taken to reduce the number of infections in the first wave, and to “flatten the curve”, this could prevent a second wave. The COVID-19 pandemic is unique in recent history due to the extreme lengths we have all gone to flatten the curve. Perhaps our efforts, if we sustain them long enough, will prevent a second wave. That’s quite an incentive.

Have those efforts actually worked? The evidence suggests the answer is a huge – yes. A recent study published in Nature found:

We estimate that across these six countries ( China, South Korea, Italy, Iran, France, and the United States), interventions prevented or delayed on the order of 62 million confirmed cases, corresponding to averting roughly 530 million total infections.

In the US that was over 5 million confirmed cases and 60 million total cases. How many deaths would this have translated into? That is still a hard figure to come by, and we won’t really know until the pandemic is over and we can review data. The case mortality ratio also varied widely among different countries. In the US at present the case mortality ratio for confirmed cases in 5.7%. If we take 5% of 5 million cases, that is an additional 250,000 deaths avoided by the lockdown.

A separate study looking only at Europe also published in Nature found that non-pharmacological measures of reducing infection prevented an additional 3.1 million deaths. We can also look at the data the other way – how many more lives could we have saved if the we locked down earlier? A study published in May found that if the US had locked down 1 week early, this would have saved 36,000 lives.

So flattening the curve by social distancing and other measures works. These measures save significant lives, and could have saved more if we had jumped on this pandemic sooner. These measures may even save us from a second wave, but that remains to be seen.

Let’s drill down a bit to what measures specifically work. David Gorski has already done an excellent job of reviewing the most recent evidence of the efficacy of wearing masks, so I won’t repeat that review. The bottom line is that wearing masks does help prevent spread, but needs to be done properly. I do want to emphasize an issue which seems to have caused confusion (based on what I encounter online and questions from my own patients). At one point the WHO recommended wearing masks if you are sick or exposed to those who are, but not necessarily if you are healthy and out in public. The CDC, on the other hand, recommended everyone wear a mask in public. The reason for the WHO’s caution on recommending everyone wear a mask was not because they don’t work, but because at the time the recommendation was made we were having a shortage. The thought was – if you are healthy and not around sick people, don’t take a mask away from a health care worker who is on the front lines. The WHO basically left it up to individual countries based on their needs and resources. In any case – wear an appropriate mask, do it properly, and do it consistently.

But masks are not a panacea. Hand washing is also critical. Do it thoroughly, do it often, and don’t touch your face with unwashed hands. Don’t touch any public surface if you don’t have to. Elbows are your friends.

And finally, social distancing is still essential, and the evidence shows that it works. But here also there are many details. Do we need three feet, six feet, or nine feet (1, 2, or 3 meters)? The greater the distance, the greater the efficacy, until you are completely out of droplet range. This is also where masks come into play, by reducing the spread of droplets. Not physically touching other people is now also the norm, and this is critical.

The question is now turning to this – for how long do we need to ban large gatherings? When do we open up restaurants, hair salons, non-essential stores, and other public places? When can we start having sporting events with fans, conferences, concerts, and conventions? The answer is – we don’t know, so we need to proceed one step at a time, measure the outcome, and go from there.

But we may be experiencing a spontaneous and unplanned natural experiment in the US. Protests over the killing of George Floyd have resulted in mass gatherings in cities around the country. Many (but not all) protesters are wearing masks, but social distancing is not being practiced. It is not my intention to debate the relative importance of the pandemic vs social justice – just to point out that we will likely discover in the next few weeks what is likely to happen when we relax social distancing.

Social distancing is also the measure that is taking the greatest toll on people mentally and economically. For example, patients in hospitals have had to go through their experience without the benefit of visitors, and family members cannot see their loved ones, even if they are dying. It can be painful, and even have a negative impact on outcomes. And of course everyone is anxious to open up the economy.

Which brings us back to the core question – will there be a second wave? The consensus seems to be – probably. We can hope that we will avoid it, but we need to be prepared for it. It is way too early to hope for a vaccine, which is at least six months away if not more. There are medications being studied, but no guarantees of a treatment at this point. The summer heat will also not automatically save us. We are a long way from herd immunity, with only a few percent of people being exposed to SARS-CoV-2 so far. This is still a new virus, and we are a naïve population.

But at least now we know what works. We have prevented millions of cases and deaths with the non-pharmacological measures – masks, hand washing, and social distancing. We may prevent millions more, and may prevent or at least minimize a second or even multiple waves. We are partly buying time to develop a vaccine and effective medications. It’s working. We need to continue the fight, even as we start to open up. The COVID pandemic is a marathon, not a sprint.

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Posted by Steven Novella

Founder and currently Executive Editor of Science-Based Medicine Steven Novella, MD is an academic clinical neurologist at the Yale University School of Medicine. He is also the host and producer of the popular weekly science podcast, The Skeptics’ Guide to the Universe, and the author of the NeuroLogicaBlog, a daily blog that covers news and issues in neuroscience, but also general science, scientific skepticism, philosophy of science, critical thinking, and the intersection of science with the media and society. Dr. Novella also has produced two courses with The Great Courses, and published a book on critical thinking - also called The Skeptics Guide to the Universe.