One of Belgium's top virologists offered his family 4 tips for surviving the long COVID-19 winter — read the full letter he wrote them

• Guido Vanham is a virologist, a microbiologist who studies the rapid spreading of viruses, who's been sending letters to his three children throughout the coronavirus pandemic.
• The text of his most recent letter is printed below with permission from his son, Peter Vanham.
• In it, Guido Vanham writes that he's optimistic about the latest major vaccine trial updates but warns that if history and previous viruses are any guide, the toughest time, winter, is still ahead of us.
• He advises a combination of four "imperfect" measures that together lead to near perfection: wearing a mask, keeping distance, ventilating the airflow, and reducing your time of interaction.

Dear Nele, Johan, and Peter,

It's been a rollercoaster few weeks, hasn't it? The bad news has been that we've been facing a severe second peak in infections here in Europe, and a similar evolution is underway elsewhere. But there's good news too: Several vaccine candidates seem to be very effective and may arrive early next year.

As we hunker down for the winter, and we unfortunately again can't see each other anymore for the holidays — your mom and I are an at-risk group, because of our age — I wanted to remind you of a couple of measures we can take to reduce our risk of getting sick, or infecting others, until a safe vaccine is here.

I do believe there is now a light at the end of the tunnel.

Two pharmaceutical companies said this week their vaccine candidates are very effective against the new coronavirus. The companies — Pfizer/BioNTech and Moderna — announced that early trial results indicate an effectiveness of their vaccine of over 90%. And that is very positive indeed.

But what does their statement mean in practice?

What these companies announced is the preliminary results of the phase 3 human trials of their vaccines candidates. The phase 3 trials are the last test phase, and in it, many thousands of people got either the vaccine (group A), or a placebo (group B), and were then screened for a couple of months as they returned to their regular lives, to see if they got COVID-19.

In both trials, about 100 of the people who participated got COVID-19. But what matters, for "effectiveness" evidence reasons, is that only a handful (5-10) of those who tested positive, belonged to the group A who was effectively vaccinated against the virus. The other 90 or so had had the placebo, and thus weren't protected. From there, the companies conclude that their vaccines are 90-95% effective against COVID-19.

Why can they make that conclusion? Well, think about it.

Group B — the control group in the trial — effectively got no protection against the virus, because they got a placebo. If 90 people among them got the virus, you'd expect that a similar number of people in any other random group of similar size would also get the virus. But, of those in group A, only 5 to 10 got the virus. The (reasonable) assumption then is that the vaccine protected all others: 80-85 people out of 90 people didn't catch the virus = approx. 90-95% effective protection thanks to the vaccine.

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You can of course ask yourself: If the vaccine works, why would anyone still get infected?

That's a fair question, and the answer is that not all humans have the same immune system. Vaccinology, just as most medical sciences, is not an exact science like mathematics. But what matters in this quest for a vaccine — what is crucial — is that they are well over 50% effective. The figures from Pfizer and Moderna, at first view, look better than for instance the flu vaccine (but still may be lower than the very effective "childhood vaccines" such as measles and tetanus).

So, is 90% effectiveness good or really good? I'd say it's really good, because it helps us fight the virus in two important ways: One, it protects 90% of those injected, with either no or only minor negative side effects (because that was an important step in the vaccine tests too — that they're safe and don't make you sick). And two, the more people are vaccinated, the less the virus can circulate, and the less chances that someone without a vaccine can still get infected, too.

In fact, vaccines are regarded by many virologists as the only ethical way — and the most effective way — to achieve the infamous "herd immunity."

If enough people get vaccinated, then we form effectively a human shield — or "herd" — for others.

The other way to achieve herd immunity is where everyone gets the virus, some may get sick or die, and the rest then develops antibodies. But that's seen as unethical because it leads to deaths and suffering, and overflowing hospitals. In addition, quite a few people who got infected in the first wave and developed antibodies, nevertheless got infected again during the second wave. Unfortunately, coronaviruses in general are known to induce only temporary immunity.

Whether any of the vaccines will induce long-lasting protection or regular "reminders" will be needed (like we have with the annual flu shot) also remains to be seen. So far, it looks as if we will have a good vaccine soon, but it's not a "magic bullet" and we should not forget about the simple and cheap "non-pharmacological measures" that can protect us from getting COVID in the meantime as well.

So I also want to remind you, as you spend much more time inside now that the weather is getting cold, that there are "imperfect" ways to protect yourself before any vaccine is here.

And that will be important, because if history and previous viruses are any guide, the toughest time is still ahead of us. With the Spanish Flu, and with many other viruses, most people got infected, and got sick or even died, during the winter season. For us, that highest risk season is now.

So what can you do? Well, I'd advise a combination of four imperfect measures. Together, they lead to near perfection. They are wearing a mask, keeping distance, ventilating the airflow, and reducing your time of interaction.

Many people may argue against any of these measures because they are only partially effective in stopping the spread of the virus. But what you should now is that even "half effective" measures exponentially get better when combined. Consider the case where two people meet in a room, one person is infected, and not taking any measures would lead to 100% chance of transmission. And consider that each individual measure taken reduces infection risk by 50%. Then

• Not doing anything = 100% chance of infection
• Infected person wears mask = 50% chance of infection
• Non-infected person wears mask = 50% chance of infection
• Ventilation = 50% chance of infection
• Keeping distance = 50% chance of infection

If you combine the measures, however, something interesting happens: 1 x 0.5 x 0.5 x 0.5 x 0.5 = 0.0625 or approximately 6% chance of infection is left! And consider now that many of these measures can protect by more than 50%. With for example 75% reduction in infection rate for each measure, the combined risk of infection drops to 1 x 0.75 x 0.75 x 0.75 x 0.75 = less than 0.1%.

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There's a similar logic at play in the length of time you meet someone, or the kinds of interactions you have with them.

Peter, remember how I told you that it was OK to play football outdoors back in September, but that you needed to stay out of the locker room? That's because in the outdoors, any kind of particles evaporate in seconds, whereas they'll keep "hanging around" for hours in a small confined space with moreover many people in it.

You can look at it another way too. Each time you breathe, you breathe out millions of particles, and when you're infected, some of them will contain the virus. For you to infect another person, these virus particles have to travel quite a way: first, from the breath of one person through the air, then into the air you breathe, and then into your lungs, where they may or may not attach to your blood cells and then start to spread from there.

If you're infected, you're a foot away from someone else, and you cough straight into their face, you can be quite sure the virus particles will manage to get to susceptible cells in their throat or lungs and infect them. In fact, Nele, when I got a cold a few weeks ago, I'm quite sure I got it from Miles, who had a cold, and sneezed in my face when we were playing. It scared me a bit at the time, and we again stopped seeing the grandchildren when cases went up, but fortunately it wasn't COVID-19.

But the situation is immediately very different when you're further apart from someone, the person doesn't sneeze or cough, or does so while wearing a mask, you too wear a mask, and you're in a ventilated space, where air continuously refreshes. So that's what I advise that you do in the coming months. Don't stop your lives, but take many imperfect measures, because they can protect you and those around you.

This is how we get through the winter, and then onto spring.

I know the holiday season is coming, and we would all very much like to see you for it. But as you've gathered by now, as a scientist, I tend to favor rationality over sentimentality in these measures. A long holiday dinner, inside, and with many people, is about as risky of a situation I can imagine for us. The odds are good when we take many partial measures, but for many healthy holidays ahead spent together the odds are even better when we skip just one holiday spent all together now.

Stay safe, and speak soon,

Dad

Peter Vanham is head of the International Media Council at the World Economic Forum, and a member of its COVID-19 Taskforce. He lives in Geneva, Switzerland.

Guido Vanham, MD, PhD, is the former head of virology at the Institute for Tropical Medicine in Antwerp, Belgium.