Photographer: Akos Stiller / Bloomberg
Photographer: Akos Stiller / Bloomberg
The road to removing Covid-19 is long and paved with uncertainty. Many countries have this vaccines to generate enough immunity in their populations so that SARS-CoV-2 is not able to find people susceptible to infection, which causes the transmission of coronavirus to slow down and eventually stop. But even with the launch of highly effective vaccines, vaccination coverage may not reach that level, the so-called herd immunity threshold – anytime. For one thing, it is it is not known what level of immunity is required and whether the vaccines will be powerful enough to achieve. There is also the threat of emerging variants of coronavirus that may weaken the effectiveness of vaccinations.
1. Can Covid-19 be eradicated?
No, so far only one human disease, smallpox, has officially occurred eradicated; that is, reduced to zero cases and kept there for a long time without continuous intervention measures. Smallpox was eliminated thanks to a highly effective vaccine and the fact that humans are the only mammals that are. naturally susceptible to infection with smallpox virus that causes disfiguring, sometimes fatal disease. The human being is the only known reservoir poliovirus, but still spreads some countries, causing paralyzing diseases, despite the widespread use of effective immunizations and a 32-year-old patient global eradication effort. SARS-CoV-2 is thought to persist in horseshoe nature and is known to infect minks, cats, gorillas, and other animals. Removing the virus would require banishing it from all susceptible species, which is not feasible. In countries that have successfully suppressed Covid-19 cases, the elimination of the disease has been proposed.
2. What is elimination?
That’s when efforts have been made to suppress an outbreak zero new cases of disease or infection in a defined area during a sustained period. There is no official definition of how long it should be. One proposal is to make it 28 days, which is twice as long as the outer range of the incubation period of SARS-CoV-2: the time elapsed between infection and onset of symptoms. Some countries, such as New Zealand, have achieved zero new cases over long periods with border closures, blockades and diligent case detection and isolation. Durant a pandemic, which is an outbreak of a new infection on every continent, that keeps the elimination of any infectious disease nationwide is a challenge, if not impossible, due to the threat of the virus re-entering the country by infected international travelers.
3. Will vaccines eliminate Covid-19?
It’s hard to say. It is not known what a proportion of the population needs to have immunity to stop the circulation of the coronavirus or if even the most potent vaccines will be able to prevent it from spreading. One study estimated that to stop transmission, 55% to 82% of the population should have immunity, which can be achieved by recovering from an infection or by vaccination. However, the immunity of the herd it was not achieved in Manaus, the capital of the state of Amazonas, in Brazil, even after 76% of the population had become infected. However, there is reason to believe that mass inoculations will have a more powerful effect because vaccines appear to get stronger and longer lasting protection than a previous infection.
4. How effective will the vaccines be?
There is good evidence that the shots made by Pfizer Inc.—BioNTech SE i Moderna Inc. it is very effective (up to 95%) to prevent recipients from developing the same Covid-19. However, no data have been published on its ability to prevent people from developing asymptomatic infections or transmitting the virus to others. The gold standard in vaccinology is to stop infection and disease, providing the so-called sterilizing immunity. But it is not always achieved. The measles vaccine, for example, prevents infection by preventing vaccinated people from spreading the virus, while the measles vaccine prevents whooping cough has good protection against serious diseases, but is less effective in stopping the infection. Encouraging, a the study of the Modern Covid vaccine in monkeys suggested that it would reduce, if not completely prevent, subsequent transmission of the virus. Clinical trials using The AstraZeneca Plc vaccine indicates that it may be less than 60% effective in stopping infections, so herd immunity is unlikely to be achieved even if everyone in a population receives two doses.
5. How do virus factor variants intervene?
Researchers have studied the ability of antibodies in the blood of patients recovered from Covid-19 to block new fast-spreading variants B.1.1.7, 501Y.V2 and P.1 first reported in the UK, South Africa and Brazil. Some research indicated the potential of these strains to escape the immune protection provided by natural infection. The scientists warned that laboratory studies are only indicative and that there is no evidence that this is happening in the community or that antibodies generated by vaccines will be less effective against the new strain.
6. Should Covid-19 vaccines prevent infection to curb cases?
No. Vaccines it doesn’t have to be perfect to get a benefit to public health. New Zealand vaccinologist Helen Petousis-Harris points to rotavirus and chickenpox as examples of diseases that have been “virtually eliminated by vaccines that are very good at preventing serious disease, which are very good at preventing any disease, but which do not completely prevent infection in everyone “Since SARS-CoV-2 spreads by respiratory particles from the throat and nose of an infected person, a vaccine that reduces the amount of virus in the airway or reduces the frequency that a person Infected cough can decrease the likelihood of it being transmitted to other people and the number of effective reproduction (Re), which is the average number of new infections estimated to come from a single case. Mike Ryan, head of The World Health Organization’s emergency program told reporters on Jan. 25 that instead of focusing on eliminating SARS-CoV-2, success should be seen as “reduce the ability of this virus to kill, to put people To the hospital, to destroy our economic and social life “.
Explosion to elimination
A model of how it can work
Source: Los Alamos National Laboratory (Wuhan R0 and serial interval)
7. What happens if Covid-19 is not removed?
David Heymann, Chair of the WHO Strategic and Technical Advisory Group on Infectious Risks, warned in late 2020, “it appears that the fate of SARS-CoV-2 is endemic.” Endemic viruses circulate continuously in the community, often causing periodic spikes when disease characteristics and human behavior patterns favor transmission. Examples include norovirus, the notorious cause of gastroenteritis in cruises, and countless viruses, including four coronavirus, which cause the common cold, especially during the winter.
8. What can be the implications?
It is unknown how things will evolve, but researchers have begun to define scenarios. People who have survived Covid-19 and vaccines against it are likely to be protected against the disease for some time. Probably that re-exposure to the virus or a booster vaccine strengthen their protection. As more and more people develop immunity in this way, the virus will find those who are not yet immune, as long as the herd’s immunity is not established to protect them. This would mean that people who cannot be vaccinated (because their immune system is compromised, are allergic to vaccine ingredients, or are too young (none of the vaccines authorized in Western countries have been approved for children)) will remain vulnerable. Some scientists have predicted that once the endemic phase and primary exposure to the virus in childhood are reached, SARS-CoV-2 may occur. no more virulent than the common cold.
The reference shelf
- Devi Sridhar of the University of Edinburgh and Deepti Gurdasani detail the difficult lessons learned from a largely uncontrolled epidemic of Covid-19 in Manaus, Brazil.
- Anita Heywood and Raina MacIntyre of the University of New South Wales explain the eradication, elimination and suppression of the disease and what elimination of Covid-19 would seem. MacIntyre also presents principles of vaccine programs for the control of Covid-19.
- QuickTakes related to how hesitation threatens to delay the end of the pandemic, why? delaying the second shot of a Covid-19 vaccine is messy, why mutated variants are as worrisome as coronavirus transmitted, the deployment of vaccines, if possible forced to be vaccinated, the coronavirus treatments and the unanswered questions about the virus.
– With the assistance of Alisa Odenheimer