SINGAPORE - Covid-19 has not been shown to be more deadly than the flu, said local experts responding to two recent studies that say Omicron, while not as virulent as earlier variants, caused more fatalities in the last winter season than influenza.
Almost all Covid-19 infections today are caused by Omicron and its sub-variants.
The first study, by the United States Department of Veterans Affairs (VA), looked at more than 11,000 people who were hospitalised after confirmation of either Covid-19 or the flu, between Oct 1, 2022 and Jan 31, 2023.
The results, published online by the Journal of the American Medical Association on April 6, found that 6 per cent of Covid-19 patients died, against 3.7 per cent who had the flu.
The article said: “Compared with hospitalisation for influenza, hospitalisation for Covid-19 was associated with a higher risk of death. The risk of death decreased with the number of Covid-19 vaccinations.”
The second study, by the Rabin Medical Centre in Israel, compared outcomes among 167 hospitalised Covid-19 Omicron patients and 221 patients admitted for flu in December 2021 and January 2022.
This study, which has not been peer-reviewed, was a special early release from the European Congress of Clinical Microbiology and Infectious Diseases, which is meeting in Copenhagen, Denmark, from last Saturday to Tuesday.
In this cohort, the mortality rate was 26 per cent for patients hospitalised with Omicron against 9 per cent of those with the flu.
Dr Alaa Atamna, who led the research team, said: “A possible reason for the higher Omicron death rate is that patients admitted with Omicron were older with additional major underlying illnesses such as diabetes and chronic kidney disease.”
Covid-19 is of particular interest now following news of a more virulent variant dubbed Arcturus, which has caused a surge of infections in India. There was also a spike in infections here at the end of March.
In the week of March 26, the Ministry of Health (MOH) reported 28,410 Covid-19 infections – almost double the 14,467 reported the previous week. The number of cases over the previous three weeks was also higher than in the first two months of 2023.
However, that jump in cases did not presage a new wave of infections, as the number dropped to 16,018 in the week of April 2.
On the other hand, the number of flu cases has been increasing, with confirmed cases more than doubling each month – from 96 in January to 421 in March – based on the MOH monitoring of polyclinic cases, which is used as a yardstick for infection rates in the country.
Dr Asok Kurup, an infectious diseases specialist in the private sector, said: ”I am personally seeing several cases of severe influenza infection requiring hospitalisation.”
He said he has already seen about six older patients with severe influenza this year. There were also three younger patients, aged 17 to 33, who had to be hospitalised, though none needed intensive care.
Dr Kurup said the flu should not be trifled with.
“Not enough people are getting vaccinated, especially over the last few years. So the flu is back with a vengeance.”
Professor Ooi Eng Eong of Duke-NUS Medical School, a medical doctor specialising in microbiology, said the two foreign studies were too short and not suited to compare the deadliness of the flu versus Covid-19.
He added: “Genetic drifts that occur over the course of months and even years in influenza viruses can give rise to strains with greater propensity to cause severe lung infection.”
Professor Paul Tambyah, an infectious diseases specialist at National University Hospital, agreed with Prof Ooi that the studies were not designed to compare mortality rates, and that the severity of the flu bug varies from year to year.
He added that previous studies have shown that Singapore gets about 50 deaths a month from the flu. The latest Covid-19 data from MOH shows there were 12 Covid-19 deaths in January and five in February.
Associate Professor Alex Cook, vice-dean of research at the NUS Saw Swee Hock School of Public Health, said the VA study showed mortality only among those hospitalised, and not of those infected.
He said: “It’s not a like-for-like comparison, and I don’t think that saying ‘Omicron is more severe than flu’ is warranted.”
His colleague, Associate Professor Hsu Li Yang, pointed out that the studies merely showed the number of hospitalised patients with Covid-19 or the flu who had died, and not that they had died of Covid-19 or the flu. Some patients may have been hospitalised for some other problem, but happened to be infected.
Said Prof Hsu, who is an infectious diseases expert by training: “My own take is that both are non-trivial illnesses in the elderly.”
Professor Leo Yee Sin, executive director of the National Centre for Infectious Diseases, said whether there is a seasonal pattern or a predictable pattern for Covid-19 is uncertain as the virus is still evolving.
She said the disease can be mild and inconsequential to younger adults, but can be severe in older people as there is an “age effect”.
“We have to do our part to protect our elderly and those vulnerable. Keeping an updated vaccination against the Sars-CoV-2 (virus) is critically important for the older population.”
All the experts agreed that vaccinations will continue to play an important role in reducing severe illness and death in older people and others who are vulnerable because of other illnesses they may have.
Said Prof Ooi: “I think these studies strongly reinforce the notion that vaccination is critical for preventing severe Covid-19. How frequently booster vaccinations against Covid-19 are needed in the more vulnerable group really depends on the ongoing studies.”
While Prof Hsu said he is not sure if vaccination is the way to go for Covid-19 the way it is for the flu, “perhaps this is the less harmful practice for the elderly as far as Covid-19 is concerned, until we have better data and evidence”.
Added Prof Leo: “The mRNA vaccine is highly effective but it is limited in durability – to whom, when and how frequently to give booster doses needs further study.”