This article was last updated on March 16, 2020.
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Coronavirus. This is the name of a family of viruses, including several that are known to cause 15 to 30 percent of common colds. Named for spiky projections from their protein coats that give a crown-like-(coronal) appearance under electron microscopy, coronaviruses are classified into four groups –alpha, beta, gamma, and delta– but they all fall into a larger category of viruses, namely viruses that use a molecule called RNA as the genetic material. Prior to the turn of the century, the mention of such a virus would barely get you a nod from any researcher in a department of virology, or infectious disease, but that has changed. Say the word coronavirus today, and it will evoke fear, and for a good reason. One newly discovered coronavirus, called “2019 novel coronavirus” (2019-nCoV), causes flu-like symptoms with severe illness in the lower respiratory track, such as pneumonia and bronchitis, called “coronavirus disease 2019” or, shortened, Covid-19. Covid-19 is similar to a different coronavirus known as “severe acute respiratory syndrome” (SARS) that first emerged on the scene in 2003. Since being identified in Wuhan, China, in late 2019, 2019-nCoV has caused 2,169 deaths due to Covid-19. That’s as of the writing of this post, March 16, 2020, when about 180,000 cases have been confirmed in 133 countries.
What do these data mean in terms of actual danger for you, for your children, for a developing baby that you may be carrying, and for your family and friends, if you do not live in the region of Wuhan, China, where the Chinese government has set up a quarantine ring?
One way that public health officials try to get a useful answer to this type of questions is simply by dividing the number of deaths by the number of cases. This produces what’s called the “case fatality rate”, also called the “mortality rate”. Using the numbers listed above, we would be looking at a fatality rate of approximately 2 percent due to Covid-19, except that officials don’t actually have a reliable estimate because it’s very early in the epidemic and the number of subjects with Covid-19 keeps changing on a daily basis. Essentially, there are not enough data to know how deadly Covid-19 is for those who have contracted it.
Now, I have just used the word epidemic, without defining it, so let’s unpack that just a bit. It’s not actually the case fatality rate that determines if something is an epidemic. You can have an epidemic of a disease that is not very deadly, while something can be deadly without being an epidemic. The defining characteristic of an epidemic is that it’s spreading, the number of cases is on the rise. Such spreading is related to a value known as R0 (pronounced “R naught”, the “R” stands for “reproduction”), which is basically the average number of people who become infected as a result of contact with an infected person. If each person with a particular virus infects one other person, on average, then the R0 for that condition is 1.0. This would not be an epidemic, because, for every person who catches the virus, another person would either recover, or die, so the number of cases would not increase. If R0 = 2.0, on the other hand, then each person with the virus infects two other people, each of whom then infects two people. As of February 24, the R0 for 2019-nCoV had been estimated in the range of 2.0 to 2.5, with an incubation period of 2 – 14 days (outliers: 0 – 27 days).
For perspective on what this means, it is useful to discuss two other coronaviruses that have proved deadly since the turn of the century. One of these is the SARS virus, which had an R0 in the range of 2-3 during a notorious outbreak in 2003, which it also had a mortality rate in the range of 10 percent. The other is called Middle East respiratory syndrome (MERS), which was first recognized around 2012 with an alarming mortality rate close to 34 percent, but with a low R0, so the number of confirmed cases has been only about 2500 since that time. It’s also useful to discuss measles virus, which is not a member of the coronavirus family, but I’m mentioning it because it had a notoriously high R0, ranging from 12-20, back in the days before the advent of measles vaccination. Since measles vaccination is extremely effective, measles is not an epidemic in most places, but it spreads alarmingly fast among populations of people who refuse vaccines, much faster than the spread of Covid-19. While the mortality rate from measles is much lower than for any of the three coronaviruses that we have discussed, being much more contagious, measles would be devastating, if not for the vaccine, as it was in the days prior to measles vaccination. Finally, for still more perspective, you should consider influenza –the flu, the numbers of which dwarf those of Covid-19. According to estimates by the US Centers of Disease Control and Prevention (CDC), influenza strikes 9 to 45 million people, each year, in the United States alone, leading to 140,000 to 810,000 hospitalizations and causing death in 12,000 – 61,000 people (based on numbers obtained since 2010).
How coronavirus compares to flu, Ebola, and other major outbreaks (source: National Geographic, February 7, 2020).
As for the significance of Covid-19 for pregnant women, very few data are available to draw any conclusions, but experience with SARS and MERS can provide some insight. Although only a small number of cases of these diseases have been documented in pregnancy (*see details at the end of this article), studies suggest a potential association between SARS and spontaneous abortion (miscarriage), fetal growth restriction, preterm labor and delivery, as well as maternal death. Similarly, MERS in pregnant women has been associated with severe neonatal illness (requiring treatment in the neonatal intensive care unit) as well as neonatal death. Of note, the current belief is that, unlike HIV and Zika, SARS and MERS are not capable of maternal-fetal (vertical) transmission.
Therefore, the risk for the fetus to be infected is low. If a newborn was diagnosed with SARS or MERS, the infection probably occurred during or after birth. A similar scenario is expected for Covid-19.
As worrying as this may be, it is important to keep in mind that we are talking about a very small number of pregnant women suffering from SARS and MERS, and trying to figure out from that what the danger might be from Covid-19 during pregnancy. We don’t know the answer yet, but we do know that, outside of China, influenza is a much greater danger, whether you are pregnant or not, simply because it affects millions of people. Consequently, you should do all that you can to avoid coming down with the flu, including getting a flu shot and being vigilant about hand washing. You should also have all of your other vaccines up-to-date.
Most of this article has consisted of very bad news, but there is a silver lining to this story, that, due to advances in biotechnology over the past few years, scientists have been able to learn about 2019-nCoV rapidly. Within days after recognizing the outbreak, health officials had sequenced the genome of the virus using a technique call RT-PCR (which translates the viral RNA genes into a DNA, which is then amplified so that it can be sequenced), followed by sequencing. This provided accurate knowledge of the viral protein to enable rapid diagnosis of large numbers of people and also to begin work on a vaccine. Several years ago, the mere sequencing of such a viral genome would have amount to a dissertation project of a PhD student working for four years. Using the newly created diagnostic tests, health authorities both inside and outside of China are able to hone in on people who are infected, get them help, help to locate their recent contacts, and keep them from infecting others. As the technology improves, public health authorities will be able to stop outbreaks with increasing speed. In addition to working toward a vaccine, scientists are also working toward the goal of selecting and testing antiviral drugs that may possibly be effective against the virus.
Given all of this, one question that you may have is “what to do?” if you’re suffering from symptoms known to result from the 2019-nCoV virus, such as dyspnea (difficulty breathing), along with fever, aches, an pains. The answer is that you probably have the flu. Given the relatively low number of people suffering from the novel coronavirus compared with flu, the chances are very low that you are infected with Covid-19. This is despite the fact that there have been a handful of confirmed cases of Covid-19 in the United States, Canada, the United Kingdom, and other countries where people read this blog.
Another question that you may have is whether there is any benefit to wearing a mask, like those that you may have seen in videos of people in Chinese cities, or maybe that you have seen in crowded malls or airports. Like SARS, MERS, as well as the various coronaviruses that cause common colds, 2019-nCoV transmits from person-to-person through droplets in the air and also through touch. Researchers believe that you can acquire the virus through the air, if you come within approximately two meters (six feet) of an infected person. While it is true to that special masks, the masks that healthcare workers may wear, or masks that are worn during surgery, offer protection, it is not clear that the ordinary masks that people wear in the streets will prevent airborne contamination in either direction. Some researchers suspect that, if the ordinary masks do any good, it’s because they are preventing the wearer from touching his or her face.
*There is no evidence that the two other coronaviruses that have caused major outbreaks — severe acute respiratory syndrome (SARS) and Middle East respiratory syndrome (MERS) — are capable of vertical transmission. There are 12 pregnant women known to have been infected with SARS during the 2002–03 pandemic. Four of the 7 (57%) women who were infected in the first trimester had a miscarriage. Of the remaining five women infected in the second to third trimester, two (40%) had a newborn with growth restriction and four (80%) had a preterm birth (one spontaneous; three induced for maternal condition). Three (25%) of the 12 infected women died during pregnancy. In a review of 11 pregnant women infected with MERS, ten (91%) presented with adverse outcomes, six (55%) neonates required admission to the intensive care unit, and three (27%) died. Two neonates were delivered prematurely for severe maternal respiratory failure.