Virologists were already predicting a second wave of coronavirus infections months ago. The more people break the rules of conduct and restrictions introduced to curb the pandemic, the greater the risk of sucha second wave. Now, it seems to be rolling in.
In many countries, lockdown restrictions are no longer being as strictly enforced. Germany, Spain and Greece were among the first countries in Europe to ease such measures.
The World Health Organization (WHO) has warned that the coronavirus may never fully disappear. It has stressed the possible consequences if people take the coronavirus lightly and revert to behavior patterns that prevailed before lockdown measures were put in place.
In many countries, shops have reopened, as have restaurants. In Australia, the government has tightened restrictions again after several cases of infection among guests in pubs and bars.
People's desire to travel is also on the rise once more — another reason for increased infection rates. Too many people are congregating in too small spaces; parties are taking place again. The risk of infection is rising, worldwide. In Germany, there was a sharp uptick in the number of infections at the end of July. The reproduction rate R also went up again.
The reproduction number R
The reproduction rate indicates how many other people one ill person infects on average. This number helps health authorities to better predict infection patterns. For example, if R is 3, it means that one infected person will infect three more people. If the reproduction number is 1, the infection rate remains about the same.
In Germany, this reproduction number rose to above 1 at the end of July. This could be due, among other things, to holidaymakers who once again blithely mingled in large crowds even though the pandemic is far from over.
If the infection numbers go down, it is an initial success. However, if things go the other way and the reproduction rate increases, this could indicate a second wave of infections.
The United States and Brazil have recently experienced the most dramatic increases, followed by India and South Africa. In Brazil alone, well over 2 million people have already become infected with the virus. According to the Brazilian Ministry of Health, more than 2,600,000 people were infected by the end of July.
The second wave
There is no uniform international standard for how a second wave is defined. Even the WHO has no clear guidelines. WHO spokesman Christian Lindmeier wrote in an email to DW: "The term refers [only] to new outbreaks that have occurred after an initial decline. The same applies to a 'third' wave."
At the beginning of the pandemic, virologists were already warning against a further wave of infection and appealed to the population not to see falling infection numbers as a license to act carelessly.
Scientists are comparing the coronavirus with the Spanish flu, which raged from 1918 to 1920. According to the WHO, it claimed between 20 and 50 million lives worldwide.
That pandemic ran in three waves. The second wave was much worse than the first and caused many more deaths. Between the individual phases, the virus mutated. That could also be the case with the novel coronavirus.
What if the virus mutates?
Every virus can mutate, i.e. change. At best, a virus becomes weaker through mutation. This means that it is less dangerous and claims fewer victims. For this to happen, however, a large number of people must already have developed immunity to a virus. Whether this is the case with SARS-CoV-2, researchers do not yet know.
People develop immunity against most viruses. When infected, the body produces antibodies and, if these succeed in fighting off the virus, a person becomes immune. The virus can then no longer harm that person.
But it is unclear whether this is also completely true of the novel coronavirus. More and more cases indicate that some COVID-19 sufferers no longer have any detectable antibodies in them after just a few months. This could mean that they could become infected again.
With a serological test, experts can determine whether someone has produced antibodies against the virus. But such a test does not provide any information about whether the person is then immune to the virus and, if so, for how long. Scientists are now trying to answer these questions.
During times when the coronavirus pandemic has been at its most severe, there were often voices suggesting that only so-called herd immunity could contain the disease. Herd immunity occurs when a high percentage of the population is already immune so the pathogen can no longer spread as quickly. Some 70% to 90% of the population would have to be immune to a virus to stop it.
Medical journal The Lancet recently published a study on herd immunity indicating that herd immunity against the coronavirus will be "difficult to achieve." Scientists at the Madrid Carlos III Health Institute, the Spanish Ministry of Health and Harvard University in Boston were involved in the study, which was the largest European antibody study to date, involving 60,000 people.
The investigations showed that only about 5% of all Spaniards had formed antibodies against the virus.
The virus likes it cold
Viruses feel comfortable in cold environments. This is a reason, for example, why several coronavirus outbreaks have been in slaughterhouses, where temperatures are usually quite low. By contrast, viruses generally do not spread as quickly in hot weather as in cold.
At warmer times of year, there should thus be fewer infections with viruses. In addition, if it is cold outdoors, people spend more time indoors, where there is much less exchange of air than outside. This means that virus-laden aerosols — tiny airborne droplets — can spread more easily.
At the beginning of the pandemic, experts assumed that SARS-CoV-2 was spread by means of larger droplets, such as those produced by coughing and talking, and by smear infection, i.e. contact with an infected surface. But we soon learned better: The virus can also linger in the air in the form of aerosols and be transmitted in this way.
If it is dry and cold outside, these are ideal conditions for the virus. The aerosols then remain in the air much longer than on warm days. But precautions are always necessary — and winter has not yet even begun in the northern hemisphere.