Two experts explain what other viruses can teach us about COVID-19 – and what they can’t

As of 19 March, there have been more than 200,000 confirmed cases of COVID-19 across the globe, according to the World Health Organization (WHO).

It took more than three months to reach the first 100,000 confirmed cases, and only 12 days to reach the next 100,000, a sign that the speed of transmission is increasing.

In a recent major coronavirus outbreak, SARS, in 2002-2003, it took six months for cases to exceed 5,000 in mainland China. COVID-19 did that in just one month.

Here, David Duong, MD, MPH - Instructor in Global Health and Social Medicine at Harvard Medical School and Harvard Medical School Director of Global Primary Care and Social Change, as well as a member of the World Economic Forum’s Global Future Council on Health and Healthcare - and his colleague Todd Pollack, MD - Assistant Professor of Medicine at Harvard Medical School and Country Director for the Partnership for Health Advancement in Vietnam, a Harvard Medical School Global Program - explain some of what we know about COVID-19.

How does COVID-19 spread?

POLLACK: There are two major ways that the virus is thought to spread: from person to person through respiratory droplets when an infected person coughs or sneezes, and from contact with contaminated surfaces, where the virus can survive for hours to days at a time. In this case, a person can get COVID-19 by touching a surface that has virus on it, and then touching their eyes, nose or mouth.

Can a warmer climate reduce the spread of COVID-19 and other viruses?

DUONG: With influenza, there is a seasonal pattern – it spikes up in the winter and goes down in the summer. But is it the virus itself or are there other factors? The four factors to look at are the environment, so the temperature and humidity. Then the human factor: we tend to stay indoors, closer to one another [in winter months], and that increases transmissibility. The third is our immune system. There’s some hypotheses that our immune system is lowered in colder months because those of us in the northern hemisphere, we don’t see the sun as much and the sun helps generate something called vitamin D, which is an immune-system booster. The fourth thing is the ability for the virus itself to replicate given the number of susceptible hosts – as the proportion of susceptible contacts declines, the epidemic peaks, and eventually declines.

We have to take all those factors into account. Coronaviruses are enveloped viruses and the envelope itself tends to be a bit more fragile with increased heat and increased humidity. But that’s not the case for all enveloped viruses.

Studies that came out of the Middle East around MERS-CoV, the last coronavirus epidemic, found that it did prefer colder temperatures and lower humidity. With the SARS one, it tended to follow that as well. But it did not go away because of warmer weather, but rather because of the political choices that were put into place to control that epidemic, such as social distancing and isolating cases and quarantining their contacts. And that was the major reason we saw the SARS epidemic go away; SARS did not go away because of the warmer temperature effect. So, with the new virus, the SARS-CoV-2, which causes COVID-19, although we could expect it to behave like other coronaviruses, at this point in time, we just don’t know. And we don’t have enough data because it’s so new, so for entire economies or countries to make policy decisions based on the behaviour of other similar viruses would not be prudent or advisable.

POLLACK: Even if it behaves the same as the influenza virus in terms of these factors, that doesn’t eliminate transmissibility, it might just reduce it somewhat. And one major difference between SARS-CoV-2 and influenza is that SARS-CoV-2 is a novel virus - no one in the world has any immunity to it. So in the summer months in the northern hemisphere with influenza, the transmissibility goes down for a number of factors, and that’s enough to shut off transmission. And that may be partly because a lot of the population has immunity already, because of vaccination or partial immunity from previous infection. With SARS-CoV-2, even if transmissibility is reduced in the summer, it is very unlikely that’s going to have enough of an effect that the virus will disappear, because there are enough susceptible people to sustain transmission.

Can MERS and SARS tell us anything about how the new coronavirus pandemic might develop?

POLLACK: Each of these viruses seem to affect humans differently, so I think it’s difficult to extrapolate from MERS and SARS to COVID-19. SARS had a much higher mortality rate. And the number of asymptomatic or mildly symptomatic people after infection was quite low. So, it was a lot easier to do isolation and contact tracing with SARS, because if you were infected, then it was quite obvious. And so SARS really went away because of public health measures. But with COVID-19 it’s much harder to find and track those who are infected. It’s a good thing that it’s less deadly than SARS and MERS, but the [higher] transmissibility makes it much more difficult to control.

The WHO has warned of an ‘infodemic of misinformation’ around COVID-19. How concerned are you about it?

POLLACK: On the one hand, you have information that is communicated in a way that is causing people to be scared and panicked, which has led to some unhelpful behaviours such as panic buying and stealing of hand sanitizer or other supplies from hospitals. On the other hand, we had this idea that the virus is not dangerous for young, healthy people, and especially in the US and Europe, this created a sense of security or lack of concern about getting infected. However, we know now that it can be dangerous even for younger people, and maybe more importantly, younger people contribute to the spread of the virus to older people or people who have pre-existing conditions that make them more vulnerable. And, that’s what ultimately leads to the hospitals becoming overwhelmed with too many patients and shortages of supplies, which exacerbates the problems. So clear, consistent, and transparent communication is so important.

DUONG: With this virus at this global scale, there’s so much uncertainty and that causes a lot of anxiety and fear in people. Government’s job is to communicate around that uncertainty and communicate the decisions that they’re making based on what is fact and what is conjecture. Governments in places like Singapore and Taiwan have said: This is what we know. This is what we’re assuming. So therefore, these are the measures that are put in place. And that really helps calm the population. Transparency in the communication process with governments is so important at this point in time. Especially in an uncertain situation when we have new data that comes out every single day that may contradict the old data.

What ought to be the priorities for governments and healthcare systems?

POLLACK: The good news is that we have examples of countries that have had major outbreaks and found ways to slow them. In China, in Wuhan, the outbreak was successfully contained through aggressive quarantine and isolation measures. In South Korea, we saw the importance of widespread testing as part of the containment strategy. They are testing tens of thousands of people every day and isolating those who test positive from others and allowing for less restrictive measures for the rest of the population. The key thing is to keep infected people away from uninfected people. And how to do that depends a bit on society and your resources and what you have available, but some combination of aggressive testing, isolation of infected people, and social distancing is what we've seen to be effective.

What are the key things that people need to know about COVID-19?

POLLACK: People should understand that even if they are at lower risk for serious health consequences, they can contribute to the continual spread of the virus in their community, which affects those who are at higher risk of a bad outcome. That’s the purpose of social distancing and everyone should take it seriously even if their individual risk is low.

DUONG: This is a ‘novel’ virus for a reason, because it’s so new, we don’t understand much about it and the science is still changing. However, given what we do know, the best thing that the general public can do right now, is to ‘flatten the curve’, through social distancing measures. And we know that soap and water helps kill the virus. So wash your hands, practice social distancing, and if you have symptoms, report them and pay attention to them. But we need to be prepared for uncertainty.

There could be a seasonality effect, but there is no amount of seasonality effect that will work better than the current mitigation and suppression efforts that we’re doing to control this virus. That still trumps everything else.

POLLACK: We should all be prepared for the fact that this COVID-19 is likely to be an issue for some time to come.