Thursday, May 19

Covid-19 in Europe: Be careful when comparing countries | View


Opinions expressed in View articles are those of the authors alone.

Once again, COVID is making a comeback in Europe. But not all countries are in the same situation. Why?

It’s an easy question to answer, but confusion reigns in the press, on social media, and even among some scientists and epidemiological modelers.

The answer is a basic epidemiological principle, population immunity: a concept that any young epidemiologist learns early in his career, as I did during my first month at the Centers for Disease Control and Prevention (CDC). ) in 1976.

The immunity of the population is as relevant today with SARS-CoV-2 and its many variants as it was then. It is simply the percentage of the population that has had an immune response to an infectious agent or vaccine, and this response is not necessarily one that prevents another infection.

Measles infection in children provides an immune response that provides lifelong protection against reinfection, and the immune response from the measles vaccine provides lifelong protection against measles infection.

A high percentage of the population’s immunity against measles can, in fact, stop transmission and eliminate the virus by creating a “herd immunity” that stops the transmission of the virus from person to person.

We are not so lucky with SARS-CoV-2. Those who have had a prior infection do not appear to be fully protected against reinfection, although most appear to be protected, for a time yet to be determined, from serious illness if reinfection occurs.

And most people who have received a full series of vaccinations are protected against serious illness and death if they become infected after vaccination. We are extremely fortunate to have such a wide variety of vaccines developed and produced in such a short time.

Learning to live with SARS-CoV-2

Because the current generation of COVID-19 vaccines does not protect against infection in all vaccinated, and because natural infection does not prevent reinfection, SARS-CoV-2 is becoming an endemic infection that will likely remain. in human populations, as do the other four endemic coronaviruses that cause the common cold.

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And since we have learned to live with HIV, an infection believed to have arisen in human populations of the animal kingdom sometime in the early 20th century, we must learn to live with SARS-CoV-2. We must hope that the immunity of the population will keep the infection mild and that severe COVID syndrome prolonged after infection can be prevented by vaccination.

All of this is not bad news. In fact, this is good news, and as the population’s immunity to SARS-CoV-2 infections increases in those who have been vaccinated and those who have already been infected, the infection will likely have a milder course of the disease. disease, milder than in many of those who have not had a previous infection or vaccination.

In summary, COVID-19 provides protection against serious illness and death in most people who have had a previous infection with COVID-19, or in those who have been vaccinated, and as more evidence emerges we will see if the same is. valid for the Omicron variant.

Be wary of comparisons across Europe

Comparisons of COVID-19 are being made between European and non-European countries based on reported COVID-19 cases.

This makes the story easy for journalists, but many times the story is not accurate because ‘cases’, as defined by the World Health Organization, are reports of people with a positive diagnostic test, and this, for Of course, it depends on the testing strategy used in each case. country.

Testing strategies vary widely in European countries, from screening programs in schools to diagnostics in healthcare settings.

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There are numerous websites that provide insight into the differences in the number of people tested. Statista.com, for example, reports Germany, with a population larger than the UK, is estimated to have carried out nearly 82 million tests since the start of the pandemic, compared to more than 355 million in the UK.

So with these differences, how can valid comparisons be made between European countries? And is it really necessary to compare them?

In most European countries, the national focus has not been on reported cases, but on hospital admissions, ICU capacity, and deaths.

Decision makers have used increases in these rates as a reason to “lock in”: either by using localized restrictions where there is known transmission, or broader restrictions across the country.

These rates would be better if comparisons were made between European countries and could be more informative if additional information such as vaccination status, presence of comorbidities and age were also reported.

Further blockages may be bypassed in some countries

At some point in the past 18 months, most European countries have locked in their economies, and people ranging from office workers to school-age children have been isolated at home during these periods.

The enclosures have prevented serious illness and death by preventing SARS-CoV-2 transmission and infection, especially in the elderly and those with severe comorbidities.

But the blockages, in addition to having a devastating effect on livelihoods, have also decreased the virus’s ability to spread, preventing the population from acquiring immunity against natural infection, but also preventing any associated long-term COVID.

Currently, some European countries reporting low COVID-19 hospital admissions, ICU admissions and deaths are trying to postpone closures.

Hopefully, if they have developed a high population immunity to the current known variants of concern, and hopefully to the newer variant, Omicron, which is being intensively studied in South Africa and elsewhere, they will be able to continue down this path.

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But in the end, to understand the differences between European countries, it all comes down to understanding the immunity of the population.

And by current understanding, vaccination or natural infection provides an immune response that greatly decreases the risk of severe illness and death from SARS-CoV-2 infection.

Vaccines are still the answer

We are very fortunate to have the alternative of increasing the immunity of the population through vaccination instead of waiting for the immunity of the population and its harmful aftermath to develop naturally.

Vaccination coverage is a good indicator of the level of immunity of the population among European countries, some of which are plagued by strong anti-vaccination movements.

So, currently, European countries find themselves in an uneasy balance: different vaccination rates and population immunity, and different strategies to drive the virus into endemicity.

It would be easy to conclude that European countries should let the virus in quickly, to compensate for the uneven distribution of vaccines and hope that those with comorbidities and prone to developing prolonged COVID will be spared.

However, the right path is to bring vaccines to the populations of Europe, remembering that there is an urgent need, indeed an obligation, to ensure a more equitable distribution of vaccines in all countries of the world.

David Heymann is Professor of Infectious Disease Epidemiology at the London School of Hygiene and Tropical Medicine, formerly of the World Health Organization, Public Health England, and the Centers for Disease Control and Prevention.


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