Note: This article continues the Pandemic series which includes Pandemic Part 1: A Primer on the Biology of the SARS-CoV-2 Virus and the Terminology that You are Hearing, Pandemic Part 2: Pandemics of the Past, Pandemic Part 3: Getting Your Flu Shot and Other Vaccines, and Part 4: How the Testing Works for COVID-19.
In an earlier segment, we considered some pandemics of the past, such as the influenza pandemic of 1918 and the Asian flu of 1956-58. The history of these pandemics raises concerns as to possible effects of the COVID-19 pandemic on pregnant women and on the fetuses that they carry inside, as does experience with previous 21st-century viral outbreaks that have struck fewer people than COVID-19, but with dramatically high rates of severe illness and mortality. The latter group includes Ebolavirus, although, for insight on COVID-19, we are concerned mostly with viral diseases whose main life-threatening effects and method of transmission involve the respiratory system. Thus, 21st-century examples to highlight include the influenza A (H7N9) outbreak of 2013, the influenza A (H1N1) outbreak of 2009 (“swine flu”), and two human coronavirus diseases: severe acute respiratory syndrome (SARS), occurring in 2003, and Middle East respiratory syndrome (MERS) of 2012. Although the As, Hs, and Ns are included here for naming purposes, for the sake of this article, you can think of the viruses causing these diseases as falling into two broad categories: influenza viruses and coronaviruses. The current pandemic, COVID-19, falls into the latter category and is caused by a virus called SARS-CoV2.
As the pandemic has unfolded since January, you have likely learned that being infected with SARS-CoV-2 entails a very broad spectrum of severities, ranging from being entirely asymptomatic (you feel normal and thus are unaware that you are infected) to having common cold symptoms, to having flu-like symptoms and worsening respiratory symptoms, to having what doctors call acute respiratory distress syndrome (ARDS). The latter requires admission, either to an intensive care unit (ICU) within a hospital or to one of a growing number of ICU facilities that are being built rapidly to manage massive numbers of COVID-19 cases. In addition to requiring mechanical ventilation through what’s called an endotracheal (ET) tube (a tube that is inserted down the throat), ARDS furthermore can lead to a variety of other life-threatening complications. While mechanical ventilation can keep a person alive as her body learns to fight off the virus, the mortality (the rate of death) appears to be fairly high, thus far, for those who get to the point of requiring ventilation. Consequently, one thing that scientists are trying to learn is why COVID-19 reaches a severe state in some people but can be more limited in most others.
Much less than an understanding, what we have at this point is statistics, describing which categories of people are more or less vulnerable to develop severe disease if they do become infected. In this respect, you have probably heard that age and the presence of other diseases constitute the major factors. Statistically speaking, if you are over the age of 65, you are at higher risk of getting to a critical stage and of dying compared with younger people, but a person with another disease, such as cancer, heart disease, high blood pressure, or uncontrolled diabetes, is at high risk, even if she or he is younger. Lifestyle factors also affect the risk. As far as we know, smoking cigarettes and other tobacco products does not increase one’s risk of catching COVID-19 in the first place, but smokers who do become infected carry a significantly higher risk of becoming critically ill and of dying compared with infected non-smokers. So smoking is even more unwise during the current pandemic than it was in the pre-COVID-19 era, whether you are pregnant or not.
But what about pregnancy and COVID-19? Pregnancy is not a bad habit like smoking, nor is it a disease, like atherosclerosis or diabetes, but it does change your physiology considerably. The changes include function of the immune system, which has a complex relationship with the rest of the body during pregnancy because it has to allow the embryo/fetus to flourish and not be expelled as an infectious parasite. Thus, it is thought that there are periods during pregnancy when you are more susceptible to infectious disease compared with non-pregnant women of similar age and health status.
So for insight from history, let’s start with the worst outbreak of the modern era, the 1918 influenza pandemic. The sheer scale of the causative virus, a type of H1N1 influenza A, was huge as it is estimated to have infected approximately 500 million people, about one third of the human population at the time. Of these 500 million people, the virus is thought to have killed at least 50 million and some estimates have suggested the death toll may have been twice that number. This means that the case fatality rate of the 1918 flu was at least 10 percent, which is roughly the same as the death rate of the 2003 SARS outbreak, although for SARS the total number of cases and number of deaths were approximately 8,000 and 800, respectively, so it was a much smaller scale disease. With both SARS and the 1918 flu, however, the consequences for pregnant women were substantial. Reporting on cases and deaths in 1918 and even in the 1950s was not as thorough or reliable as such reporting is today, but available information includes reports of death rates in the range of 27 to 45 percent for infected pregnant women during the influenza pandemics of 1918 and 1956. This means that the outcome for pregnant women with those infections was worse than for the general population. Dovetailing with all of this, studies have also shown that pregnant women with the 1918 and 1956 influenza diseases suffered elevated rates of complications. As for the fetus, there were reports of elevated rates of spontaneous abortion (miscarriage) during the 1918 flu and elevated rates of defects of the brain and spinal cord, fetal death, preterm labor and delivery, and spontaneous abortion in connection with the 1956 flu. Similarly, studies have suggested a possible association between SARS and spontaneous abortion, fetal growth restriction, preterm labor and delivery, and also maternal death. In the case of MERS, which struck fewer people than SARS, but killed more than 34 percent, infection was associated with severe neonatal illness and also neonatal death. There is no evidence that the coronaviruses that cause SARS and MERS (known as SARS-CoV1 and MERS-CoV) are capable of vertical transmission, which is to say transfer from mother to fetus through the placenta or through body fluids during delivery, but respiratory transfer through droplets (for instance through coughing) is another matter.
As for the 2013 influenza A (H7N9) and the 2009 influenza A (H1N1), they were reported to cause complications and death and higher rates in infected pregnant women and also were associated with adverse outcomes for the fetus, such as spontaneous abortion and preterm labor and birth.
This all sounds really bad as we consider COVID-19 and pregnancy. However, a new study, early analysis of the COVID-19 pandemic’s effect on pregnancy, in this case, 38 pregnant women with COVID-19 has found a couple of encouraging things. First, as expected based on the SARS/MERS experience, the researchers found no evidence of vertical transmission to the fetus, but second, in sharp contrast with SARS and MERS, the new study did not find an elevated rate of maternal death. Possibly this has to do with the fact that, although it is pandemic affecting an alarmingly high number of people, that COVID-19 has a lower rate of severe cases compared with the previous two human coronaviruses. A major caution, however, is that, despite knowing the statistics of older people and people with other illnesses being at higher risk, it’s not really understood yet what makes some people more vulnerable in the sense that they develop the full-blown, life-threatening disease. So stay tuned to remain up to date as we learn more about this illness.