As the current wave of unprecedented global disruption from COVID-19 slowly begins to recede and life starts to return to normal, albeit a different normal, people around the world are wondering if there will be a second wave of COVID-19.
Given that this is a brand-new (i.e., novel) human coronavirus which has only been under our microscopes for the last 5 months, no one at this time has that answer. However, if one is pragmatic when looking at previous pandemics, it would be fair to conclude that it is somewhat probable that there will be a second wave of COVID-19.
Three Significant Pandemics
In the last 100 years, excluding the current COVID-19 pandemic caused by the SARS-CoV-2 virus, we have experienced five pandemics – all caused by a new (novel) influenza virus.
The three with the most significance were:
- 1918 - 1919, caused by the H1N1 influenza virus (Spanish flu);
- 1957 - 1958 due to the H2N2 influenza virus (Asian flu); and
- the H3N2 influenza virus (Hong Kong flu) in 1968 – 1970.
The deadliest pandemic recorded in the modern era to date occurred in 1918 - 1919 and killed an estimated 50 to 100 million persons worldwide.1 This pandemic was unique due to the fact that very high death rates were seen in healthy younger persons aged 15 to 34 years. It appears that this pandemic occurred in three distinct waves.2 The first wave began in the spring and summer of 1918 and was relatively mild and did not attract much attention. In the fall of 1918, the second and most severe wave occurred, and the spread was global. Despite involving a highly pathogenic and transmissible strain of influenza, this second wave's severity can be explained, at least in part, by the military context in which it developed, with large numbers of soldiers and allied personal (all of a relatively young age) moving about the world.3
In addition, at this time the public health system in most countries was underdeveloped and unprepared for a pandemic. Antibiotics to treat secondary bacterial infections had not been developed, and containment was not consistently practiced. In early 1919, a third, milder wave occurred. The pattern of these three waves was not universal and some regions even reported a persistence of influenza infection and/or recurrence into 1920.2
The 1957 - 1958 Asian flu pandemic, although milder in nature, was still significant. It resulted in 1 to 2 million deaths worldwide, with higher mortality in younger age groups.4, 5 Like the 1918 Spanish flu, the Asian flu appeared in waves, although this time only two occurred, with the second wave proving deadlier than the first.4 The first wave initially appeared in the spring and summer of 1957. The second wave occurred in the fall of 1957 and appeared to coincide with the re-opening of schools and the subsequent broader, community-wide transmission.6
One decade later, the next of the severe pandemics emerged, the 1968 - 1970 Hong Kong flu. A unique feature of this virus was its accelerated spread due to extensive air travel, which had not been seen in previous pandemics. Once again, there was a shift in the age distribution of mortality toward younger age groups.7 The Hong Kong flu is estimated to have caused between 500,000 to 2 million deaths worldwide.8 There were two waves associated with the virus. The first began in July 1968, driven in part by Vietnam War veterans returning to the United States.9 The first wave was from 1968 until the winter of 1969, and the second wave occurred in the late fall and winter of 1969 and 1970. Most influenza-related deaths in the first wave occurred in the United States (70%) and Canada (54%), while in Europe and Asia, 70% of the deaths due to the pandemic were in the second wave.7 The North American experience contrasted with previous patterns of a more severe second wave.
2009 H1N1 Pandemic
In 2009 - 2010, we experienced the less significant H1N1 Swine flu pandemic, which again exhibited wave behavior that varied geographically. The number of deaths globally was between approximately 151,700 and 575,400.10
Pandemics tend to occur in waves, but there is a significant geographical variability and we are unable to accurately predict why, how, or when the waves will occur, but based on previous pandemics, it would seem probable that there will be a second wave of COVID- 19.
However, given the advances in public health, medical therapy, health care delivery, and the increased production of personal protective equipment, we are certainly in a better position today to deal with any additional waves that may occur. Given the inherent uncertainty of pandemics, and drawing on our previous experience, I think we would be wise to remember the words of Sir Winston Churchill, “This is not the end. It is not even the beginning of the end. But it is, perhaps the end of the beginning”.