TEHRAN - Questions about coronavirus (COVID-19) – how it behaves, who it strikes, and how bad it can get – are spreading almost as fast as the virus itself. The quest to get some answers will take some time before we can come up with reliable statistics.

In six months during 2003, SARS infected a total of about 8,000 people and killed about 770 in just a few locations: China, Taiwan, Hong Kong, Toronto, and Singapore, with a handful of cases in a few other cities before it was contained and ran out of steam.

The first positive case for COVID-19 was detected on December 1. Just three-and-a-half months later WHO declared COVID-19 a pandemic.

What is alarming about this disease is the speed at which it is spreading worldwide. According to WHO website dated March 11, in the past two weeks, the number of cases of COVID-19 outside China has increased 13-fold and the number of affected countries has tripled. WHO reports more than 118,000 cases in 114 countries, and 4,291 people have lost their lives.

From the time of this report WHO has made the assessment that COVID-19 can be characterized as a pandemic. However, “90 percent of the cases are in just four countries, and two of those – China and S. Korea – have significantly declining epidemics,” the report added.

According to TIME magazine’s March 14 report, Italy is second on the list, with 21,157 cases, 1,441 deaths, and 1,966 recoveries. Iran is third on the list with 12,729 cases, 611 deaths and 2,959 recoveries.

During a Wednesday news conference in Berlin, German Chancellor Angela Merkel said the “consensus among experts is that 60 to 70 percent of the population will be infected” since there is no immunity for the virus. About 1,300 people have been infected with novel coronavirus in Germany as of Wednesday, but only three deaths have been reported.

We simply do not know if it will slow during the summer months, as some respiratory viral infections do. 

If it does, “be ready for at least a second wave in the fall, following the path of the 1918 influence and the 2009 influenza”, says Timothy Sly a Canadian epidemiologist while talking to Maclean's magazine.

The worst-case scenario, writes Sly, is to allow the virus to enter a population and circulate, some people will die, while the majority will acquire immunity, finally bringing the pandemic to a halt.

Important factors

Seriousness, in the context of an infectious illness, is assessed by a combination of factors. The “case-fatality rate” (CFR) is the risk of dying if you have the condition or mortality rate. For example, dandruff has a CFR of zero, Ebola ranges from 25 percent to 90 percent, and rabies is essentially 100 percent fatal. Seasonal influenza comes in around 0.1 to 0.2 percent or one to two deaths expected per thousand cases. According to the recent data, confirmed by WHO Director-General Tedros Adhanom Ghebreyesus CFR for COVID-19 is 3.4 percent, more than the previous estimates of 1.4 and 2 percent.

Fatality rates also vary based on age. No deaths occurred in nine or younger, but cases for those aged 70-79 carried eight percent fatality, and those aged 80 and older with a fatality rate of 14.8 percent. The rate was 49 percent among critical cases, and among those with pre-existing conditions to between 5.6-10.3 percent depending on condition.

A second key factor is a rate at which an infection can spread to others. That’s the “basic reproductive number” (BRN), an estimate of how many secondary infections can be expected from an average primary case. A BRN greater than one predicts continuing growth, less than one predicts the outbreak will die out, while a BRN equal to one suggests continuous low-level disease – an endemic. A BRN for SARS, for instance, was between two to five, diphtheria, four to five, and measles nine to 18. More than 10 estimates for the COVID-19 have been calculated ranging from 1.7 and 3.3.

A third key factor is incubation period (IP). In a research published in the journal Eurosurveillance, one of the most detailed estimate of the IP of COVID-19, the researchers studied 88 people who had been confirmed positive for COVID-19 virus and found the average incubation period was 6.4 days, with the range from 2 to 11 days.

Before jumping into conclusions there are doubts about the number of cases reported worldwide are accurate. Exact numbers of “confirmed” cases is not possible to find out at any given time but the numbers will be more refined with time.

COVID-19 vs other epidemics

How the coronavirus compares to SARS, swine flu, Zika, and other epidemics. While some of those examples were deadlier, they were far more limited in scope.

COVID-19 is not as deadly as SARS epidemic of 2003, which killed about ten percent of the 8,098 confirmed cases of the respiratory illness.

It is also far less deadly than the Middle East Respiratory Syndrome, or MERS, which killed 34 percent of 2,500 since it was first reported in 2012 in Saudi Arabia.

With a mortality rate (CFR) of 3.4 percent, COVID-19 is more severe than 2009 outbreak of H1N1, or Swineflu which infected between 700 million to 1.4 billion people with mortality rate of 0.02 percent.

In 2015-16 more than 500,000 cases of Zika virus were reported with 18 deaths. Zika has been linked to a spike in birth defect microcephaly. It is transmitted through mosquitoes while COVID-19 is spread through respiratory fluids such as saliva or mucus. That is why it is so important to cover your mouth when coughing and cover your face when sneezing.