Why are there so many vaccinated people in hospital?

It may be confronting to hear there are more vaccinated people than unvaccinated people in hospital – but it’s actually a good thing.

Right now, it looks like there has been an increase in the number of people hospitalised with COVID-19 – even though they’re fully vaccinated.

This is particularly evident in Israel, where there are more vaccinated than unvaccinated people in hospital.

The bottom line is that no vaccine is 100 per cent perfect. You can still get sick and there is a chance you’ll still need hospital care – in spite of being vaccinated.

Why would that be so?

It all comes down to the size of the vaccinated population.

Imagine this scenario

To understand why this happens, we need to look at vaccine efficacy within the whole population, not just the people in hospital.

We know that COVID-19 vaccines reduce your chances of serious illness by around 80 per cent.

In trials, 80 per cent vaccine efficacy means that 80 per cent of people who contracted COVID-19 were unvaccinated, and 20 per cent were vaccinated.

Say we looked at a population of 100 people, 50 vaccinated and 50 unvaccinated. Of these, 40 people had COVID-19.

If we look at the ratios in this hypothetical example, we see that 8/40 infected people are vaccinated and 32/40 are unvaccinated. It’s clear to see that the vaccinated people fared better – in fact, that would be a vaccine efficacy of 80 per cent (1–8/40 = 80 per cent).

A population with 50 per cent vaccine coverage

However, the ratios change as vaccination rates increase – they are no longer even.

Say, instead, that there are 80 vaccinated people of our hypothetical population of 100 and only 20 unvaccinated. In this scenario, there are 29 people with COVID-19.

Let’s zoom in – We see that 16/29 people are vaccinated, but only 13 are unvaccinated. It seems like more vaccinated people are ending up with the virus, but that number is out of context.

A population with 80 per cent vaccine coverage

Instead, we can see that the overall rate of incidence has dropped from 40 to 29 as the vaccinated population reaches 80 per cent.

It also means that the percentage of vaccinated sick people (16/80 = 20 per cent) is much lower than the percentage of unvaccinated sick people (13/20 = 65 per cent).

This is the same principle that occurs as Australia’s vaccinated population increases. With higher vaccination rates, the ratio of vaccinated to unvaccinated people in hospital will become closer, but the rate of seriously ill people in the whole population will decrease.

People who wear seatbelts still die

We can see the above scenario playing out in many different situations. It all comes down to the number of people following a protocol. For example, seat belts are compulsory in Australia, so most people in car accidents are wearing a seatbelt. People that wear seat belts still get in car accidents, but fewer die.

In 1970, the year before seat belts became compulsory across Australia, 3,798 people died in car accidents. In 2019, only 1,195 people died in car accidents.

Read more: What does 80% vaccination coverage mean?

If you look at the people now in hospital as a result of car accidents, you’ll find that most were wearing a seat belt.

Of course, that doesn’t mean you shouldn’t bother with a seat belt, because if you do end up in a car accident, you’re more still 10 times more likely to die if you’re not wearing a seatbelt than if you are.

The same goes with vaccines. The data is still clear: vaccines dramatically lower your risk of severe disease, hospitalisation and death from COVID-19.

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This article was originally published on Cosmos Magazine and was written by Deborah Devis. Deborah Devis is a science journalist at Cosmos. She has a Bachelor of Liberal Arts and Science (Honours) in biology and philosophy from the University of Sydney, and a PhD in plant molecular genetics from the University of Adelaide.