Photographer: Akos Stiller / Bloomberg
Photographer: Akos Stiller / Bloomberg
The road to elimination of Covid-19 is long and paved with uncertainty. Many countries rely on vaccines to build sufficient immunity in their populations so that SARS-CoV-2 cannot find people susceptible to infection, slowing down the transmission of coronavirus and eventually stopping it. But even with the launch of highly effective vaccines, immunization coverage may not reach this level – the so-called herd immunity threshold – anytime soon. First of all, it is it is not known what level of immunity is needed and whether there will be vaccines strong enough to touch it. There is also the threat emerging variants of coronavirus that may weaken the effectiveness of immunizations.
1. Can Covid-19 be eradicated?
Not. So far, only one human disease – smallpox – was official eradicated; ie reduced to zero cases and maintained there for a long time without continuous intervention measures. Smallpox has been eliminated due to an extremely 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. People are the only known reservoir of poliovirus, but continues to spread several countries causing paralyzing diseases, despite the widespread use of effective immunizations and a 32-year-old child global eradication effort. SARS-CoV-2 is thought to persist in the horseshoe and has been known to infect minks, cats, gorillas and other animals. Deleting the virus would require its removal from all susceptible species, which is not feasible. In countries that have successfully abolished Covid-19 cases, the elimination of the disease was proposed instead.
2. What is elimination?
Then came the efforts to suppress an outbreak zero new cases of disease or infection in a defined area over a sustained period. There is no official definition of duration. One proposal is to do it 28 days, which corresponds to twice as much as the outer interval of the incubation period of SARS-CoV-2 – the time between infection and the onset of symptoms. Some countries, such as New Zealand, have obtained zero new cases for long periods of time, using border closures, blockades and case detection and isolation. During a pandemic, which is an outbreak of a new infection on the continents, supporting the elimination of any infectious disease nationwide is challenging, 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 the proportion of the population must have immunity to stop the circulation of the coronavirus or if even the strongest vaccines will be able to prevent its spread. One study estimated that in order to stop transmission, 55% to 82% of the population should have immunity, which can be achieved either by recovery from an infection or by vaccination. However, the immunity of the herd it was not performed in Manaus, the capital of the Brazilian state of Amazonas, even after about 76% of the population was infected. However, there is reason to believe that mass vaccinations will have a stronger effect, as vaccines appear to achieve stronger and more lasting protection than a previous infection.
4. How effective will the vaccines be?
There is good evidence that the shootings made by Pfizer Inc.—BioNTech SE and Moderna Inc. are very effective – up to 95% – in preventing recipients from developing Covid-19 itself. However, no data have been published on their ability to prevent people from developing asymptomatic infections or transmitting the virus to others. The gold standard in vaccinology is to stop infection as well as disease by providing so-called sterilizing immunity. But it is not always achieved. The measles vaccine, for example, prevents infection so that vaccinated people do not spread the virus, while the measles vaccine Whooping cough does a good job protecting against serious illness, but is less effective at stopping the infection. Encouraging, a The study of the Coverna Moderna vaccine in monkeys suggested that it would reduce, if not completely prevent, the subsequent transmission of the virus. Clinical trials using The AstraZeneca Plc vaccine indicates that it can be less than 60% effective in stopping infections – which makes it unlikely that the population will be immune even if everyone in a population has received two doses.
5. How do virus factor variants come in?
The researchers studied the ability of antibodies in the blood of patients recovered from Covid-19 to block the new fast-spreading variants B.1.1.7, 501Y.V2 and P.1 reported for the first time in the UK, South Africa and Brazil. Some research has shown the potential of these strains to get rid of the immune protection offered by natural infection. Scientists have warned that laboratory studies are only indicative and there is no evidence that this is actually happening in the community or if the antibodies generated by the vaccine will be less effective against the new strain.
6. Should Covid-19 vaccines prevent infection to reduce cases?
Vaccines you don’t have to be perfect to have a public health benefit. Vaccinologist from New Zealand Helen Petousis-Harris cites rotavirus and chickenpox as examples of diseases that have been “virtually eliminated using vaccines that are very good at preventing severe disease, quite good at preventing any disease, but which do not completely prevent infection in everyone.” Because SARS-CoV-2 spreads through the respiratory particles in an infected person’s throat and nose, a vaccine that reduces the amount of virus in the airway or reduces the frequency with which an infected person coughs can reduce the likelihood of it being transmitted to others the actual number of reproductions (Re), which is the average number of new infections estimated to come from a single case. Mike Ryan, chief of The World Health Organization’s emergency program told reporters Jan. 25 that rather than focus on eliminating SARS-CoV-2, success should be seen as “reducing the ability of this virus to kill, to put people in hospital, to destroy our economic and social life. ”
Explosion at disposal
A model of how it can work
Source: Los Alamos National Laboratory (Wuhan R0 and serial range)
7. What happens if Covid-19 is not eliminated?
David Heymann, Chair of the WHO Strategic and Technical Advisory Group on Infectious Hazards, warned at the end of 2020, “it seems that the fate of SARS-CoV-2 is to become endemic”. Endemic viruses circulate continuously in the community, often causing periodic increases when disease characteristics and patterns of human behavior favor transmission. Examples include norovirus, the notorious cause of gastroenteritis on cruise ships, and countless viruses, including four coronaviruses, which cause the common cold, especially in winter.
8. What could be the implications?
It is not known how things will evolve, but researchers have begun to explode scenarios. People who have survived Covid-19 and those who have been vaccinated against it will probably be protected against the disease for some time. Probably a exposure to the virus or a booster shot of the vaccine support 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 immunity of the herd is not established to protect them. This will mean that people who cannot be vaccinated – because their immune system is compromised or have allergies to vaccine ingredients or are too young (none of the vaccines allowed 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 be no more virulent than the common cold.
Reference shelf
- Devi Sridhar from the University of Edinburgh and Deepti Gurdasani detail difficult lessons learned from a largely uncontrolled Covid-19 epidemic in Manaus, Brazil.
- Anita Heywood and Raina MacIntyre from the University of New South Wales explain the eradication, elimination and suppression of the disease and what elimination of Covid-19 would look like. MacIntyre also presents principles of vaccination programs for the control of Covid-19.
- QuickTakes related to how hesitation of the vaccine threatens to delay the end of the pandemic, why The delay in the second shot of a Covid-19 vaccine is messy, why mutant variants are as worrisome as coronavirus transmitted, launching the vaccine, whatever you may be forced to be vaccinated, coronavirus treatments and unanswered questions about the virus.
– With the assistance of Alisa Odenheimer