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Asof June 22, the world had 3.75 million active Covid-19 cases. Among those, around 2% were serious or critical, and an estimated 1.5% of those were being treated with ventilators.

Let’s rewind three months to March 22, 2020. At that time, there were 224,588 active cases around the world, 5% of which were reported to be serious or critical. More people are infected now, but a lower percentage of them need ventilation treatment. Why is that? There are a few possible explanations. What follows are the five most commonly debated suggestions.

1. The virus is gradually becoming less lethal.

This hypothesis was raised in the early days of the outbreak by a minority of experts. This view is still, to this day, held by few and stands in contrast to the common convention that the virus is not mutating, at least not in a meaningful way.

Professor Matteo Bassetti, head of the infectious diseases clinic at Italy’s Policlinico San Martino Hospital, has said that “coronavirus had downgraded from a tiger to a wild cat.” Bassetti says that in the last month (compared with March and April of this year), the severity of the virus has changed and that even elderly patients, aged 80–90, are now sitting up in bed and breathing without help. Again, this is a view held by a minority of experts. The optimistic belief that Covid-19 is steadily weakening and will eventually disappear is considered highly unlikely by most.

2. Hot weather is slowing down the virus.

This, too, has been a subject of speculation and debate for months. Theories on the benefits of vitamin D treatment or evidence of clusters mainly occurring in cool climates all sparked an optimistic view that the coronavirus could fade by summertime like other similar seasonal illnesses. Research is still being published asserting that hot weather and sunshine cause the virus to decay to such a degree that a higher viral load is needed to prompt a serious condition. This is, however, inconclusive.

Other researchers found there is no link between the spread of the virus and weather conditions. In certain parts of the world, the Middle East, for example, a rise in cases has been reported despite the onset of summer. So is it possible that hot weather is causing the virus to be less dangerous? Possibly, but recent evidence suggests otherwise.

3. More tests are happening.

More tests are being done, and so more asymptomatic carriers are found. Our World in Data

This is quite a straightforward argument. In most of the world, more tests are being done. When you test more, you find more. Even President Donald Trump knows that. With more tests completed, the number of asymptomatic carriers also increases. More people are reported sick, many of them in a very mild state, which makes the percentage of those in critical condition drop. This must have some effect, although that by itself is unlikely to explain the whole trend.

4. There are better treatments.

The world is learning new information about Covid-19 every day. Along with the rising number of Covid-19 daily cases are the rising number of Covid-19 daily research papers. With new knowledge comes better and more effective treatment. Just recently, Oxford University reported that treatment with the cheap, highly accessible drug dexamethasone managed to reduce mortality rates. More research is needed, but this is definitely a good start.

Could it be that ventilators aren’t necessarily effective in all Covid-19 cases?

As there isn’t yet any proven coronavirus medication, what is definitely affecting the rate of patients needing ventilation is the evolving treatment protocol. It is quite clear that the general convention in medicine initially favored ventilation treatment, and providers believed that starting it as soon as possible was preferred. When a patient showed signs of deterioration, the protocol in many hospitals around the world was to connect an invasive respirator right away. This explains the arms race after ventilators — countries needed as many as they could get.

Over time, as new knowledge was gathered and with experience, a question started to emerge. Could it be that ventilators aren’t necessarily effective in all Covid-19 cases? Research showed that many ended up dying despite receiving treatment. Some even went so far as to say ventilators harmed patients more than they helped. Some patients developed a dependence on the ventilator and were more difficult to wean from mechanical ventilation. This could, in turn, cause chronic respiratory problems.

In some countries, the practice has now shifted considerably to no more early ventilating and efforts being made to avoid ventilators at almost any cost. Noninvasive methods now considered, such as Vapotherm, were not used during the first wave because they might cause a splatter of droplets from the patient and put staff at risk. Mind you, at that time, many medical staff were already underprotected due to a dire shortage of personal protective equipment (PPE).

5. Younger people are getting sick.

This claim is part chance and part very hard to measure. It is clear that in some places, the median age of those infected has dropped considerably. Florida is a very clear example: The median age for those infected in Florida now stands at 37 — in March it was 65. This trend has followed in Texas, Arizona, and other places. Does this age shift at least partially explain the lower rates of ICU admission and the drop in the use of ventilators? Yes. On measure, young people suffer less from Covid-19 and are less likely to need intensive care than older people.

One theory as to why the median age has gotten younger is that older people are doing a better job of protecting themselves. But how long can this continue as the disease spreads through the younger population? Probably not long. If this is the reason we’re leaning less heavily on ventilators at the moment, then we are not really fixing the problem — instead, we’re postponing it.