Photographer: Akos Stiller / Bloomberg
Photographer: Akos Stiller / Bloomberg
The road to eliminating Covid-19 is paved long and with uncertainty. Many countries count on vaccines to build up sufficient immunity in their population so that SARS-CoV-2 cannot find susceptible people to infect, causing the transmission of the coronavirus to slow down and eventually stop. But even with the introduction of very effective vaccines, the coverage of the vaccine may not reach the level – the so-called pillow immunity threshold – soon. For one thing it is not known what level of immunity is required and whether vaccines will be strong enough to achieve it. There is also the threat of emerging coronavirus variants that may impair the effectiveness of vaccinations.
1. Can Covid-19 be eradicated?
No. Till now only one human disease – smallpox – is official eradicated; that is, reduced to zero cases and held there long-term without continuous intervention measures. Smallpox has been eliminated thanks to an extremely effective vaccine and the fact that humans are the only mammals naturally susceptible to infection with the variola virus that causes the debilitating, sometimes fatal disease. Humans are the only known reservoir of poliovirus, but it still spreads in some countries, which cause crippling diseases, despite the widespread use of effective vaccinations and a 32-year-old global eradication effort. It is suspected that SARS-CoV-2 persists in nature in horseshoe iron bats, and it is known to infect minks, cats, gorillas and other animals. To eradicate the virus, it must be banned from every susceptible species, which is not feasible. In countries that have successfully suppressed Covid-19 cases, disease elimination has been suggested rather.
2. What is elimination?
It was then that attempts to suppress an outbreak led to zero new cases of a disease or infection in a particular area over a long period of time. There is no official definition of how long it should be. One suggestion is to make it 28 days, corresponding to twice as long as the outer series of SARS-CoV-2 incubation period – the time between infection and the onset of symptoms. Some countries, such as New Zealand, have achieved zero new business over long periods of time by bringing about border closures, closures and diligent detection and isolation of businesses. While a pandemic, which is an outbreak of a new infection across the continents, sustaining the eradication of any contagious disease nationwide challenging, if not impossible, due to the threat of the virus re-entering the country by infected international travelers.
Will vaccines eliminate Covid-19?
That’s hard to say. It is not known what a portion of the population must have immunity to prevent the coronavirus from circulating, or that even the most potent vaccines can spread. One study estimated that in order to stop the transmission, 55% to 82% of the population must have immunity, which can be achieved by repairing an infection or by vaccination. Herd immunity was not achieved in Manaus, the capital of the Amazon state in Brazil, even after about 76% of the population was infected. Nevertheless, there is reason to believe that mass vaccinations will have a stronger effect because the vaccines appear to be stronger and more durable than a previous infection.
4. How effective will vaccines be?
There is good evidence that the shots made by Pfizer Inc.-BioNTech SE en Moderna Inc. is very effective – up to 95% – in preventing recipients from developing Covid-19 themselves. However, no data have been released on their ability to prevent humans from developing asymptomatic infections or transmitting the virus to others. The gold standard in vaccination is to stop infection as well as diseases, by the so-called sterilization of immunity. But this is not always achieved. For example, the measles vaccine prevents infection so that vaccinated people do not spread the virus, while the vaccine for whooping cough is good for protecting against serious diseases but is less effective at stopping infection. Encouraging, a a study of Moderna’s Covid vaccine in monkeys has suggested that it reduces the transmission of the virus, if it does not occur completely. Clinical trials using The AstraZeneca Plc vaccine suggests that it can be less than 60% effective in stopping infections, making it unlikely that herd immunity will be acquired, even if everyone in a population receives two doses.
5. How can variants of the virus be activated?
Researchers have studied the ability of antibodies in the blood of recovered Covid-19 patients to study the new, rapidly spreading B.1.1.7, 501Y.V2 and P.1 variants first found in the UK, South Africa and Brazil reported, to block. Some research has indicated that these strains can escape the immune protection of natural infections. The scientists warned that laboratory studies are only an indication and that there is no evidence that they occur in the community, or that antibodies generated by vaccine will be less effective against the new strain.
6. Should Covid-19 vaccines prevent infection to limit cases?
No. Vaccines does not have to be perfect to have a public health benefit. New Zealand vaccinator Helen Petousis-Harris points to rotavirus and chickenpox as examples of diseases that have been ‘virtually eliminated’ using vaccines that are very good at preventing serious diseases, which are good at preventing any disease but which can not prevent infection in everyone . ‘ Because SARS-CoV-2 spreads through respiratory particles from the throat and nose of an infected person, a vaccine that reduces the amount of virus in the airways or the frequency at which an infected person coughs may reduce the likelihood of it others are transferred and lowered. the effective reproduction number (Re), which is the average number of new infections that are estimated to arise from a single case. Mike Ryan, head of the The World Health Organization’s Emergency Health Program told reporters on January 25 that rather than focusing on eliminating SARS-CoV-2, success should be seen as’ reducing the ability of this virus to kill people, to kill people. farm in the hospital, to destroy our economic and social lives. ”
Explosion to elimination
A model of how it can work
Source: Los Alamos National Laboratory (Wuhan R0 and Series Interval)
7. What if Covid-19 is not eliminated?
David Heymann, Chair of the WHO’s Strategic and Technical Advisory Group on Contagious Hazards, warned at the end of 2020, “it appears that the fate of SARS-CoV-2 must become endemic.” Viruses that are endemic are constantly spreading in the community, often causing periodic spikes when diseases and human behavior patterns promote transmission. Examples are norovirus, the notorious cause of gastroenteritis on cruise ships, and the myriad viruses, including four coronaviruses that cause colds in particular, especially during winter.
8. What could be the implications?
It is unknown how things will develop, but researchers have begun to carry out scenarios. People who survived Covid-19 and those who were vaccinated against it are likely to be protected against the disease for some time. It is likely re-exposure to the virus or a booster shot of the vaccine strengthen their protection. As more and more people develop immunity in this way, the virus will find those that are not yet immune, as long as there is no herd immunity to protect them. This will mean that people who cannot be vaccinated – because their immune systems are at risk, or they have allergies to vaccine ingredients, or that they are too young (none of the vaccines authorized in Western countries have been approved for children) – will remain vulnerable. Some scientists have predicted that SARS-CoV-2 once the endemic phase is reached and is the primary exposure to the virus in childhood no more virulent than colds.
The reference shelf
- The Devi Sridhar and Deepti Gurdasani of the University of Edinburgh describe the difficult lessons learned from a largely uncontrolled Covid-19 epidemic in Manaus, Brazil.
- The University of New South Wales, Anita Heywood and Raina MacIntyre explain the eradication, elimination and suppression of diseases and the elimination of Covid-19 would look like. MacIntyre also offers principles of vaccine programs for Covid-19 control.
- Related QuickTakes on how hesitant vaccine threatens to delay the end of the pandemic, why the postponement of the second ingestion of a Covid-19 vaccine is messy, why the mutated variants are so worrying how the coronavirus is transferred, the vaccine deployment, or you may be now forced to be vaccinated, coronavirus treatments and the unanswered questions about the virus.
– With assistance by Alisa Odenheimer