COVID-19 could be a seasonal illness with higher risk in winter

Reduced humidity linked to increased COVID-19 risk.

COVID-19 could be a seasonal illness

A study conducted in NSW during the early epidemic stage of COVID-19 has found an association between lower humidity and an increase in locally acquired positive cases.

Researchers at the University of Sydney discovered that a 1 per cent decrease in humidity could increase the number of COVID-19 cases by 6 per cent.

The research led by Professor Michael Ward, an epidemiologist at the University of Sydney, and two researchers from Fudan University in Shanghai, China, is the first peer-reviewed study of a relationship between climate and COVID-19 in the southern hemisphere.

“COVID-19 is likely to be a seasonal disease that recurs in periods of lower humidity,” explained Prof. Ward.

“We need to be thinking if it’s winter time, it could be COVID-19 time.”

Further studies – including those conducted during winter – are needed to determine how this relationship works and the extent to which it drives COVID-19 case notification rates.

Previous research has identified a link between climate and occurrence of SARS-CoV cases in Hong Kong and China and MERS-CoV cases in Saudi Arabia, and a recent study on the COVID-19 outbreak in China found an association between transmission and daily temperature and relative humidity

“The pandemic in China, Europe and North America happened in winter, so we were interested to see if the association between COVID-19 cases and climate was different in Australia in late summer and early autumn,” Prof. Ward said.

“When it comes to climate, we found that lower humidity is the main driver here, rather than colder temperatures.

“It means we may see an increased risk in winter here, when we have a drop in humidity. But in the northern hemisphere, in areas with lower humidity or during periods when humidity drops, there might be a risk even during the summer months. So, vigilance must be maintained.”

Prof. Ward said there were biological reasons why humidity matters in transmission of airborne viruses.

“When the humidity is lower, the air is drier and it makes the aerosols smaller,” he said.

“When you sneeze and cough those smaller infectious aerosols can stay suspended in the air for longer. That increases the exposure for other people. When the air is humid and the aerosols are larger and heavier, they fall and hit surfaces quicker.”

Prof. Ward and his team studied 749 locally acquired cases of COVID-19 – mostly in Sydney – between 26 February and 31 March.

The team matched the patients’ postcodes with the nearest weather observation station and studied the rainfall, temperature and humidity for the period January to March 2020.

The study found lower humidity was associated with increased case notifications; a reduction in relative humidity of 1 per cent was predicted to be associated with an increase of COVID-19 cases by 6 per cent.

“This means we need to be careful coming into a dry winter,” Prof. Ward said.

“Even though the cases of COVID-19 have gone down in Australia, we still need to be vigilant and public health systems need to be aware of potentially increased risk when we are in a period of low humidity.

“Ongoing testing and surveillance remain critical as we enter the winter months, when conditions may favour coronavirus spread.”

Are you concerned about a spike in the number of Australian COVID-19 cases during winter?

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    COMMENTS

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    Horace Cope
    3rd Jun 2020
    10:20am
    It should be pointed out that the 'flu vaccination is derived from the previous known infections and if there is a new virus associated with the current 'flu there will be no barrier. One can presume, therefore, that even if a vaccine can be found for COVID-19 that any variation to the strain will have no protection. We read that last year the 'flu virus caused about 3000 deaths in Australia and this pandemic has claimed just over 100. Maybe it's time to reduce the concern about health and increase the concern about the economy.
    Rosret
    3rd Jun 2020
    10:29am
    Apparently COVID-19 is not mutating like influenza but I am not a medico. - and yes, let's get the economy up and running again especially as we have to pay for all the public service pay rises out of Australia's credit account.
    Laura52
    3rd Jun 2020
    10:38am
    That is correct Rosret, this virus is stable for now but it does mutate, but slowly and the mutations are not significant for now in terms of how it will affect the properties of the virus. All viruses mutate given the right circumstances.
    sainter
    3rd Jun 2020
    11:32am
    It will be interesting to see if that figure of 3000 from the flu last year is similar to this year with social distancing,as we had none of that last year,the economy is a problem and will be for sometime to come....so all the people saying don't get to worried about covid/19 maybe the same should apply to the economy also...yes people have lost jobs and business is in strife but we've been through this before and will probably go through it again in the future.
    sainter
    3rd Jun 2020
    11:32am
    It will be interesting to see if that figure of 3000 from the flu last year is similar to this year with social distancing,as we had none of that last year,the economy is a problem and will be for sometime to come....so all the people saying don't get to worried about covid/19 maybe the same should apply to the economy also...yes people have lost jobs and business is in strife but we've been through this before and will probably go through it again in the future.
    Laura52
    3rd Jun 2020
    1:10pm
    I would be interested too Sainter...to see how the increase in social awareness of hygienic measures and social distancing has impacted the flu virus!
    Anonymous
    3rd Jun 2020
    1:41pm
    The flu vaccine is only 40% effective at it's best but it does have a feel good factor that makes people mentally feel they have had it so they won't get the flu. Covid-19 one will probably be les effective but have a similar mental effect on people.
    Anonymous
    3rd Jun 2020
    1:43pm
    Maybe that's why I never get the flu I just do what everyone else is asked to do for Covid-19 anyway and have done so all my life.
    Laura52
    3rd Jun 2020
    4:13pm
    According to the department of Health Australia: In general, influenza vaccine effectiveness has been found to vary between 30-60%. This implies that, on average, a vaccinated person is 30-60% less likely to experience the outcome being measured (e.g. influenza leading to attendance at a general practice or hospitalisation) than an unvaccinated person. The estimated effectiveness of the vaccine may depend on a number of factors – the outcome being measured, the age group predominantly affected (vaccine effectiveness is generally lower in older people than in younger adults and children), and the match between vaccine and circulating influenza strains
    Anonymous
    4th Jun 2020
    11:42am
    It is not the vaccine but your immune system that stop the flu before it takes hold. The vaccine is only a state of mind as it does not stop you getting the flu at all.
    Rosret
    3rd Jun 2020
    10:26am
    That's why they are more concerned about Victoria and Tasmania (cold and dry). However its under control so let's keep on keeping on and just take appropriate care - just as we do for the flu.
    Xmas19
    3rd Jun 2020
    10:28am
    Not sure of the science here considering that Singapore has about 80% humidity all year round and is known for its cleanliness yet has had 35,000 cases (of which 23,000 have recovered) and 24 deaths.
    Rosret
    3rd Jun 2020
    10:32am
    I think that says a lot about Singapore. They have a very high density population and to have so few serious cases has to be a positive indicator.
    Laura52
    3rd Jun 2020
    10:35am
    That's right Xmas19....this virus doesn't discriminate between hot and cold.
    Anonymous
    3rd Jun 2020
    1:47pm
    Covid-19 does not like the heat but loves hot countries with people inside in air conditioning.
    Rosret
    3rd Jun 2020
    3:49pm
    I understand it breaks down in UV sunlight and heat so the old adage of fresh air and sunshine still applies.
    Laura52
    3rd Jun 2020
    10:34am
    From my understanding, the virus is not affected by climate, as cases are still happening in the Summer overseas, with lifting of restrictions, such as in South Korea, Japan, the USA. The reason the spikes could happen here in Australia (in areas of community transmission which are still occurring, ) during the colder seasons is because of infectious people not practising social distancing or isolating themselves when ill, lack of cough and sneeze etiquette in social places such as cafes, restaurants etc as restrictions have have eased off. This virus needs hosts to survive, simple as that It doesn't discriminate between hot and cold climates.
    Anonymous
    3rd Jun 2020
    1:46pm
    Covid-19 does not like the heat and that's why it attacks your nose and lungs those being the coolest parts of your body. If we were going into summer we wold certainly not have a second wave but going into winter might just be enough to cause a second wave.
    Laura52
    3rd Jun 2020
    4:08pm
    Where is your scientific based evidence for covid-19 not liking the heat? Can you provide a link for me to analyse and review?The reason why colds and flus are more promiment in Winter is due to people being more indoors, increased contact of spreading viruses. The flu still occurs in Spring and Summer but not in a pronounced way as due to people being more in the outdoors. There have been cases of the flu in Australia in Summer and Spring.
    Thoughtful
    3rd Jun 2020
    5:54pm
    This article links the spread of virus to humidity levels rather than temperature. It would seem to me it is indicating spread through aerosol, rather than touch, in times of lower humidity and may be another reason to consider wearing masks.
    Pushkin2
    4th Jun 2020
    12:11pm
    Interesting the study was mainly conducted in Sydney, which is humid yet had high rates of infection, but in Canberra where it is dryer (and colder) rates were fairly negligible. Please explain.


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