SINGAPORE: The outbreak of COVID-19 infections that started in Wuhan, China and has now spread to almost 30 other countries including Singapore could follow the same trajectory seen in the H1N1 influenza outbreak in Mexico just over a decade ago. It could fade into something less sinister later on, said infectious disease experts.
In early March 2009, Mexico experienced outbreaks of respiratory illness and increased reports of patients with flu-like symptoms in several areas of the country.
This new human H1N1 strain, which originated from swine flu in pigs, swept across the world and by the World Health Organization's (WHO) estimate, was responsible for more than 18,000 deaths globally in the 2009 pandemic.
JUST ANOTHER FLU BUG
WHO declared the virus a public health emergency on Apr 24, 2009. Four days later, Singapore raised its Disease Outbreak Response (DORSCON) from Green to Yellow. This was raised to Orange on Apr 30, when the WHO raised its pandemic alert level from phase 4 to phase 5.
But it was not until May 26, 2009 that Singapore saw its first case of H1N1, 15 days after the Ministry of Health (MOH) revised the DORSCON alert back down to Yellow. A 22-year-old undergraduate returning from New York had developed symptoms on the flight and later tested positive for the virus.
The outbreak in Singapore peaked in Aug 2009, and the country saw 18 H1N1 fatalities in that year. By the time the DORSCON alert was lowered from yellow to green on Feb 21, 2010, about 415,000 people islandwide had been infected with the virus, with most experiencing mild illness.
“Everyone then realised that it was just another flu bug. The initial deaths in Mexico were not seen in Singapore. Very surprising,” said Dr Leong Hoe Nam, an infectious disease specialist at Mount Elizabeth Novena Hospital.
“Now when you revisit Mexico, the same virus circulates there, but it doesn’t kill that much.” This is because the threat of H1N1 eroded over the years, he added.
And the same is likely to happen for COVID-19, said experts CNA spoke to.
VIRUSES BECOME MILDER OVER TIME: EXPERTS
Professor Tikki Pang, visiting professor at the Lee Kuan Yew School of Public Policy under the National University of Singapore (NUS) said the coronavirus causing the COVID-19 outbreak is likely to stabilise and eventually disappear from public consciousness.
“This is the historical pattern of past pandemics, and happens because the virus ‘burns out’ and runs out of people to infect as a result of many factors,” said Prof Pang, citing warmer temperatures, better public awareness and public health measures.
“There is a possibility that the virus could mutate into something more ‘sinister’, (that) spreads faster (or causes) more severe disease, but, so far, we have not seen any evidence of this happening.”
According to Dr Leong, there are four circulating coronaviruses that cause the common cold, and one of them periodically causes severe pneumonia.
“I believe they came into existence much like the current COVID-19. It killed many people and virology or technology was not sufficiently established then to identify the cause of the illness. But it became attenuated with time,” said Dr Leong.
“COVID-19 will go the same way. What we need is time for it to accumulate mutations, and it will become milder.”
According to Dr Leong, there is a “natural tendency” for viruses to mutate to something milder.
If the virus is too pathogenic and it kills its host, it is unable to continue spreading. But if it is mild, it can continue to propagate and pass on to other individuals, eventually picking up mutations that reduce the virus' ability to cause disease, said Dr Leong.
He noted that increasing awareness of H1N1 treatment and availability of vaccines also contributed to the threat fading.
According to experts, H1N1 is currently a dominant flu strain in Singapore, although this may vary between seasons, and flu vaccines provide immunity against it. Countries in the region face a similar situation - Taiwan's Centre for Disease Control said earlier this month that 56 patients there had died of H1N1 flu virus-affected respiratory failure in the past three months.
In the years following the 2009 pandemic, H1N1 became less common globally, but has been on the increase in recent years, said Professor Clarence Tam from the Saw Swee Hock School of Public Health, NUS.
"This is likely because, after the pandemic, many people were infected with H1N1 and developed immunity against this influenza strain, so the virus couldn't spread as easily," said Prof Tam.
"But we know that immunity against influenza is short-lived, and as the level of immunity drops in the population, more people are now becoming infected with this strain again."
Dr Leong said: “It becomes another flu bug. And it helps with the fact that Singaporeans cannot distinguish between flu and the common cold, making the concept of flu in Singapore much milder.
“People soon became complacent of H1N1. But, some lethality maintained. If there is a bad case of influenza in the intensive care (unit), it would usually be a H1N1 (case). But overall, we see less and less of a problem.”
TRANSMISSION OF COVID-19, H1N1 SIMILAR
Speaking at a press conference on Friday (Feb 14), Minister for National Development Lawrence Wong had said that it is “clearly emerging” that COVID-19 is different from Severe Acute Respiratory Syndrome (SARS) and has more similarities with H1N1.
“The transmission mechanism of COVID-19 is different from SARS. In fact, the transmission mechanism is closer to H1N1 or influenza,” said Mr Wong.
Researchers at the National Centre for Infectious Diseases (NCID) have confirmed this, he added. Researchers found that, like influenza, COVID-19 is infectious when symptoms are mild.
Because of this transmission mechanism, COVID-19, like the flu, can spread “quite quickly”, said Mr Wong.
“With our mild symptoms, we sometimes let our guard down - we continue going out even though we don’t really feel well, and that’s how the virus transmits,” he added.
Mr Wong also said it was “a matter of time” before “a lot of people around the world” will be infected with COVID-19.
Citing the widespread community transmission seen in the 2009 H1N1 pandemic, Mr Wong said: “We’re not saying that this will happen for COVID-19. It’s a different disease than H1N1 so the patterns of transmission and the number of people contracting the disease will be different,” he said.
"But because the transmission patterns are similar to H1N1, we should be prepared for a scenario where you get wider transmission around the world.”
Prof Tam stressed that even if the risk of mortality from a virus is low, it can still cause a large number of deaths if it spreads easily, citing the current COVID-19 outbreak as an example.
“The available data indicate that this new virus is not as deadly as SARS, but spreads much more readily from person to person. Consequently, the number of reported deaths has already surpassed deaths from SARS in less than two months,” he said.
“The same applies for influenza viruses. Even though the proportion of all influenza cases that succumb to the disease is low, an estimated 300,000-500,000 people worldwide die each year from influenza.”
Adding that it is “difficult to predict” whether the COVID-19 will take the same route as the H1N1 pandemic, Prof Tam said: “The concern is that if current efforts to contain the virus aren’t ultimately enough to stamp out human transmission, it could spread rapidly across the globe causing many more hospitalisations and deaths before a vaccine can be developed or enough immunity builds up in the population to bring the epidemic under control.”