What do we know about pandemics? Interview with Ilkka Julkunen, Professor of Virology at the University of Turku

How do pandemics come about, how can they be prevented and what have we learnt from the coronavirus pandemic?

A pandemic is a global epidemic that emerges unexpectedly. Pandemics start with a microbe – usually a virus – that originates from somewhere in the animal kingdom and transfers to a human that is in close contact with the animal.

“It is possible for a novel virus that is capable of reproducing to be transmitted from one human to another, usually via the upper respiratory tract, because the population has no immunity to it. The virus will spread faster if asymptomatic people can also transmit it. It can already be transmitted a few days before symptoms appear,” says Ilkka Julkunen, Professor of Virology at the University of Turku.

All-important reproduction number

“The basic reproduction number (R0), which denotes a virus’s potential to spread, is at its lowest below one for microbial infections, which means the spread of the infection will slow down. When R is 1, a person will infect, on average, one other person, and when R is 2 a person will infect 2 others,” says Julkunen.

The R number of the Covid-19 virus was initially between 2 and 2.5. It is estimated that the R number of the UK variant is 0.5 units higher than this.

From Spanish flu to the coronavirus pandemic

Influenza pandemics have occurred approximately every 10–30 years over the past 100 years.

In 1918, a deadly influenza, knowns as Spanish flu, which was transmitted from birds to human beings, spread around the world. In 1957, the world was hit by Asian flu, in 1968 masses of people caught the Hong Kong flu and in 1977 there was the Russian flu. In 2009, the swine flu, which seemed to originate from pigs, caused considerable concern.

“The SARS coronavirus, which is likely to have originated from bats, spread around the world in 2002. Although the mortality rate of SARS was about 10%, it did not meet the criteria of a pandemic as it was not spread by asymptomatic carriers and was thus easier to control.”

The MERS coronavirus, which spread to humans from dromedary camels, was first detected in 2012 in the Arabian Peninsula. New MERS cases have been identified to this very day.

“The Covid-19 coronavirus pandemic is most likely to have originated in China. It derived from bats and was transmitted to humans via an armadillo or another animal potentially functioning as an intermediate host. The human population had no immunity to this novel coronavirus, which spreads via the upper respiratory tract in close contact even before symptoms appear. The fact that some infected people are asymptomatic helped the virus to spread,” explains Julkunen.

Future pandemics

“It is most likely that the next pandemic will originate from birds, bats or small rodents. A pandemic caused by the influenza A virus will emerge at some point, but a completely new type of virus may also start to spread. It may not necessarily spread via droplet transmission, as it may be a gastrointestinal disease similar to norovirus.”

If a virus is highly pathogenic, it is easier for it to spread via the respiratory tract, even if people are not in direct contact. If the virus is very contagious and it spreads through the air, such as measles, it will be almost impossible to stop the spread.

Pandemics can be prevented

“The most important factor is an international monitoring system that identifies all new influenza viruses and coronaviruses and other new pathogens. WHO requires all countries to report emerging epidemics within 24 hours of their identification. An early warning system is used when Ebola, yellow fever, cholera and other particularly dangerous microbial infections, are detected,” says Julkunen.

“We must also keep focusing on maintaining and developing laboratory diagnostics, and laboratory expertise must be developed further.”

What have we learnt from the coronavirus?

We have learnt that unforeseen pandemics can emerge, but that we can also protect ourselves from them. The spread of infections can be avoided by reducing contacts, by using masks, and by observing social distancing rules and strict coughing and hand hygiene.

“Society must control a pandemic and provide information and diagnostics in a professional way and it must maintain society’s basic functions at a high level. Sufficient resources must be used to prepare for pandemics. Smooth cooperation and openness between the authorities is also of paramount importance,” says Julkunen.

Vaccinations and immunity of the population

If a virus is new, the population will have no immunity (known as herd immunity) against it. Immunity can be achieved by either having the disease or through vaccination. Since it would be unethical to allow a disease to spread throughout the population, efforts must be made to prevent the disease effectively.

“Vaccination is used to increase the immunity of the population. It is estimated that vaccination coverage of 70–80% of the population will probably be enough to put an end to the coronavirus epidemic, because there would not be enough people susceptible to the virus to allow it to keep circulating in the population. In Finland, this situation could be achieved by the autumn if we receive enough vaccine doses and the population’s vaccination compliance remains high,” says Julkunen.

“Vaccine development has been very rapid, and we have been very lucky, as the immunity produced by all the vaccines purchased by the EU seems to be good. Yes, we will still conquer the coronavirus pandemic!”

 

Text by: Leena Koskenlaakso