Will we ever land in ‘Zero Kovid-19’? An immunologist weighs in

Most scientists agree that stringent control measures, efficient contact tracing, testing and isolation, as well as social disturbances and wearing of masks, are necessary to limit the spread of SARS-CoV-2. South Korea, Taiwan, China and New Zealand have successfully used all these methods to suppress the virus.

Some have also called for a zero COVID-19 approach, attempting to eradicate the virus rather than preventing its spread.

New Zealand almost became successful, but after 100 days without a case, new infections emerged from international sources and other unknown sources.

While it is possible to flatten the curves using these control measures, it is more difficult to obtain zero COVID-19 with them.

This may be possible for some island countries, but the New Zealand example suggests that this is necessary to prevent the virus from being imported again. This would probably require long and severe travel restrictions and rigorous testing of pre and post-trip passengers.

Given that there is little appetite to close borders for long periods of time, and community control measures alone are not sufficient to eradicate the virus, currently zero is not possible. But this can happen in the future if we use different methods.

Immunity is the best strategy

The most effective method containing COVID-19 exploits the body’s natural defense system: the immune system.

Recovering from a viral infection is usually associated with the development of immunity. Infection with SARS-CoV-2 to prevent infection is not yet known, but still there are very few examples of people.

Most infected people develop antibodies against the virus, and those who do not develop symptoms cannot produce antibodies, the infection may still activate the immune system’s T cells, which provide an alternative defense. So it seems that infection generates immunity in most people, at least in people.

Knowing this, some scientists have recently suggested that the virus should be allowed to spread to populations – while protecting the old and vulnerable – to allow herd immunity to develop.

This is where enough people in a population have become immune to prevent a disease from spreading freely. This threshold ranges from 90–95 percent for highly infectious viruses such as measles. Some have suggested that it may be less than 50 percent for SARS-CoV-2. The general consensus is that it will be around 60–70 percent.

But the percentage of people who have been infected and recovered from SARS-CoV-2 is currently nowhere near it. Studies testing for antibodies suggest that about 3 per cent of people in Dublin had the virus.

In New York City, the figure is much higher: 23 percent. But many more people have died as a result of high rates of infection in New York, even taking into account its large population.

And Sweden, which had adopted a liberal policy involving the epidemic, which resulted in higher numbers of cases, caused 10 times of deaths per million people, as did neighboring Finland and Norway.

The impact of a second wave will probably be less in places where many people have already been infected, but if the threshold for herd immunity has not been reached, the population as a whole will still not be protected.

And attempting to reach that threshold through natural infections will result in many more deaths in at-risk groups: older people, obese people, and those with underlying medical conditions.

On top of this, some who are infected develop long-term health complications, even if their initial infection is not very severe.

So for most, the risks associated with chasing herd immunity make it an unacceptable strategy to suppress the virus, let alone eliminate it.

Vaccines won’t cure soon

However, achieving herd immunity through vaccination has, in principle, the ability to obtain us for the elusive zero COVID-19.

Vaccines have reduced the incidence of diphtheria, tetanus, measles, mumps, rubella, and Haemophilus influenzae type B to near zero in many developed countries.

SARS-CoV-2 has over 200 vaccines in development. But there is a high bar to eliminate COVID-19. Any vaccine will need to be highly effective both to prevent disease and to spread the virus to people who do not do it.

However, vaccines currently have their sights set on much lower targets, along with development: at least 50 percent to be effective, which is the threshold required to be approved by the US Food and Drug Administration.

Creating a highly effective vaccine in the first attempt may be more optimistic. Vaccines will need to be effective in all age groups and safe to administer to the entire population. Safety is important, as any concern in any age group will reduce confidence and growth.

Vaccines will also have to be produced in sufficient quantities to vaccinate more than 7 billion people, which will take time.

For example, AstraZeneca – which is developing one of the leading vaccines – has deals to produce 2 billion doses by the end of 2021. It can take years to make enough for the whole world.

The effect will not be immediate. The last natural smallpox case was in 1977, when the World Health Organization launched a global eradication program for that disease, and nearly 200 years after the first smallpox vaccine was developed.

And it has been more than 30 years since the start of the Global Polio Eradication Initiative to eradicate polio everywhere except in Pakistan and Afghanistan.

So while an effective vaccine provides the best chance of reaching zero COVID-19, we need to be realistic about what is possible. In most parts of the world, eradicating the virus, while not inconceivable, can take significant numbers of years.chit chat

Kingston Mills, Professor of Experimental Immunology, Trinity College Dublin.

This article is republished from Conversation under a Creative Commons license. Read the original article.


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