In the last century there were three flu pandemics. That of 1918 was the deadliest. It developed in three waves: in the spring of 1918, in the autumn of that same year, and in the winter of 1919. The really virulent and deadly wave was the second, in which 64% of deaths occurred. In reality, the first wave was the least strong: it was only responsible for 10% of the deaths from that pandemic. In the second wave, changes have been documented in the genome of the virus that could explain that it was more virulent.
In 1957, a new influenza virus appeared that caused the “Asian flu”, which also occurred in three epidemic waves: the first in spring-summer 1957 and with a relatively low incidence, the second in early 1958 and the third in winter between 1958 and 1959. Mortality was higher in the second two waves. Ten years later, in 1968, a new influenza virus caused the so-called “Hong Kong flu”, which spread was slower and more irregular: it began in autumn-winter in the northern hemisphere and was followed by a second wave the following winter with a higher incidence.
The last influenza pandemic, the so-called “influenza A” of 2009-2010, did not have as much incidence and ended up having the effect of a seasonal flu. In fact, this virus ended up adapting to humans and being one of the strains that have circulated every year since then. As we can see, the second and third most lethal waves have happened with the influenza virus before.
In the case of SARS-CoV-2, the appearance of new epidemic waves will depend on the virus itself, its capacity for variation and adaptation to humans. Of our immunity, of whether we are really immunized and protected against it. And of our ability to transmit and control it.
Can the virus become more virulent like the 1918 flu?
We do not know. But, unlike the flu, SARS-CoV-2 is not the champion of variability. The flu virus also has an RNA genome, but there are eight small fragments that can mix with other types of avian or swine flu viruses, leading to new reassortments. Their capacity for mutation and recombination is much greater, which is why influenza vaccines have to be changed every year and pandemic viruses originate more frequently.
Since SARS-CoV-2 began, the genomes of several thousand isolates have been sequenced and compared, and of course the virus mutates! They all do it, but for now, as we expected, this one seems much more stable than the flu. Perhaps it is because it has a protein (nsp14-ExoN) that acts as an enzyme capable of repairing errors that can occur during genome replication.
Therefore, although in this case that definition of virus as a “cloud of mutants” remains valid, SARS-CoV-2 does not seem to accumulate mutations that affect its virulence at the moment.
But, in addition, on other occasions it has been found that viruses “jump” from one animal species to another, as in this case, over time they adapt to the new host and their virulence decreases. In other words, it is not always that a virus mutates to become more virulent, but generally the opposite. In any case, it will be necessary to continue monitoring it.
Are we already immunized against this virus?
To avoid the spread of an epidemic, the chain of transmission of the virus must be cut. This is achieved when there are a sufficient number of individuals (at least more than 60%) who are protected against infection, act as a barrier and prevent the virus from reaching those who could still be infected. This is what is called group immunity and is achieved when people have passed the disease or when they are vaccinated.
But against this virus we still do not have a vaccine. Is there group immunity against this virus? Well, it seems not. In the preliminary study on the seroprevalence of the SARS-CoV-2 coronavirus infection in Spain, one of the most important conclusions is that the national prevalence is 5%: some communities had prevalences lower than 2%, while others exceed 10%. These data were obtained by detecting IgG antibodies against SARS-CoV-2 using the immunochromatography technique, rapid tests.
What they indicate is that at most, in some areas, no more than 10% of the population has had contact with the virus. We are a long way from the 60% or more needed to achieve group immunity.
But all this is much more complex than it seems. We still do not know if having antibodies against SARS-CoV-2, that is, having tested positive in serological tests, really ensures that you are immunized against the virus. We do not know, for sure, how long these antibodies last or if they are neutralizing, if they block the virus and protect you from a second infection. Nor do we have data on cellular immunity, that other part of our defense system that does not depend on antibodies but on cells and that is very important to defeat viral infections.
It is true that, in the case of other coronaviruses, the antibodies last a few months or years and it seems that they have a certain protective effector, but this can also depend on the person (not all of them are the same). It is also true that there are some tests with plasma from patients cured of the coronavirus that is blocking the virus and have a beneficial effect on infected people, which would demonstrate that these antibodies are protective.
In tests with macaques infected with the virus, it has been shown that their antibodies do protect them against a second infection. But this has been done in macaques. It has also been suggested that having previous contact with other coronaviruses, those that cause common colds and colds, could have some protective effect against SARS-CoV-2. This has so far only been shown in in vitro tests, but it could explain the large number of asymptomatic people. Ultimately, group immunity remains a mystery.
Three possible scenarios
Taking all this into account, three possible models have been proposed.
1) A second much more intense wave in winter 2020 followed by smaller waves throughout 2021. This scenario would be similar to flu pandemics, but this coronavirus is not flu, it does not have to behave the same. This scenario could require a return to some type of more or less intense confinement measures during the autumn-winter to avoid the collapse of the health system again.
2) Several epidemic waves over a period of one or two years. This first epidemic peak that we just suffered would be followed by repetitive waves that would occur consistently for a couple of years until disappearing sometime in 2021-22. The frequency and intensity of these outbreaks would depend on the control measures of each country.
3) Small outbreaks without a clear pattern of new epidemic waves. This first wave would be followed by small outbreaks that would fade little by little, also depending on the control and containment measures of each country. This scenario would not require a return to such drastic confinement measures, although the number of cases and deaths could continue for a time.
In any case, it seems that we cannot rule out that the SARS-CoV-2 virus will continue to circulate among us for a while. Perhaps it ends up synchronizing with the winter season and its severity diminishes. Even if there are no new epidemic waves, including a new respiratory virus that can have very serious consequences for an important group of the population in the list of dozens of respiratory viruses that visit us each year is not good news. Every flu season the emergency rooms of many hospitals are saturated, adding a new virus is a problem.
Control and prevent outbreaks: stay ahead of the virus
The virus has not disappeared. You can continue to leave dead on the way. This is what is happening in other countries that had already finished their first wave before us, such as South Korea. In Spain there have also been outbreaks in some cities during the start of the de-escalation. In most cases, it has been related to population agglomerations (parties or family meals). But we cannot be eternally confined, nor can we sterilize all environments.
To reduce the frequency and intensity of these outbreaks, two actions are essential:
On the part of citizens: avoid contagion
We already know how the virus is transmitted and that, fortunately, it is easy to inactivate it. The infections are more frequent in closed environments or with many people.
Let’s not forget: a lot of people, close together and moving around is the best for the virus. Avoid crowds, distance between people, use of masks, frequent hand hygiene, cleaning and disinfection (in that order), follow the Health recommendations. This is what must be demanded of the citizen, we cannot relax.
By health authorities: track the virus
We cannot continue behind the virus as we have done up to now, we must take the lead.
A system must be put in place capable of detecting an infected person at the slightest symptom, being able to track and obtain information from their contacts, carry out clinical follow-up and PCR and serological tests, and if necessary isolate them.
Detect an outbreak and isolate it. This requires personnel, equipment, and diagnostic systems. And we must be prepared so that the health system does not collapse again. This is what we have to deal with right now, what we have to dedicate all the resources to, not doing massive tests on the entire population, to take “a still picture” of the situation. Decisions have to be for health reasons, not political. This is what must be demanded of our governments, they cannot relax either.
If you have been in close contact without the precautionary measures with someone who has had symptoms of COVID-19, within 2 meters for more than 15 minutes, you should isolate yourself for 14 days, and you should require the health authorities to do you I test the person with symptoms and you.
There may be a second or more waves, or there may not be. Now we have put out the fire, but we have not extinguished it, there are embers that can fan the fire. The relaxation of confinement measures is not because we have defeated the virus, it is because we also have to save our livelihood. A very long confinement can also cause deaths. We are not going to end the virus, we can avoid it. We can mitigate its effects.
What happened cannot happen again: this time we do have to protect the weakest. And that depends on citizens and governments.
Ignacio López-Goñi, Professor of Microbiology, University of Navarra
This article was originally published on The Conversation. Read the original.
