Health officials around the world are fighting to vaccinate enough people to stop the spread of COVID-19, but what qualifies as “enough” is still an open question.
The goal is to reach “herd immunity,” which is when enough people have immunity, either from vaccination or from a past infection, to stop the uncontrolled spread.
Herd immunity does not make a person immune, and outbreaks can still occur. It means that a virus no longer leaps easily from person to person, helping to protect those who are still vulnerable to catching it.
No one knows for sure what the herd’s immunity threshold for coronavirus is, although many experts say it is 70% or higher. And the appearance of variants further complicates the image.
Here’s what is known about the herd’s virus and immunity.
HOW IS THE THRESHOLD IMMUNITY THRESHOLD CALCULATED?
It’s a formula based on how contagious a virus is – or how many people catch the virus from an infected person, on average.
But the calculation only provides a broad target for when there could be a large decrease in the spread. The figure could also vary by region.
“It’s not 64.9, it’s terrible and 70.1 is fantastic,” said Dr. Walter Orenstein, an infectious disease expert at Emory University.
Orenstein notes that vaccination levels and other factors that affect the spread could differ even within a city.
HOW DO WE KNOW THAT WE HAVE REACHED THE HUMAN IMMUNITY?
Proof that we are approaching herd immunity would be a “break in the transmission chain,” said Ashley St. John, who is studying the immune system at the Duke-NUS School of Medicine in Singapore.
But don’t expect any big statements that we have reached this stage.
To determine whether to relax the restrictions, health officials will monitor trends in infection and hospitalization as vaccinations are launched. And these decisions will probably start long before the ideal herd immunity threshold is reached, although they will be gradual and vary by region.
In IndiaFor example, scientists believe that more people will have to be protected in densely populated cities, where the virus is spreading faster than in its vast rural area.
India plans to look for antibodies in humans nationwide to find out what percentage of its nearly 1.4 billion people have already been infected, said Dr. Jayaprakash Muliyil, who advises the government on virus surveillance.
The effectiveness of the vaccine also plays a role. Fewer people need to be vaccinated to get the immunity of the herd if the shootings are more effective.
HOW DO CORONAVIRUS VARIANTS AFFECT SERIAL IMMUNITY?
It depends on the protection that the previous infection or vaccination offers you from the variant.
If vaccines prove to be less effective against a variant, it would be necessary to vaccinate an even larger section of the population or update existing vaccines. to make them more effective, Orenstein said.
So far, it seems that the photos offer at least some protection against the most worrying variations. But scientists are still studying the situation and worried about other mutations.
Variants stressed the importance of vaccinating people as soon as possible. Slowing down transmission is essential because viruses can move when they infect humans.
SHOULD THE REQUEST IMMUNITY BE GLOBAL?
The global immunity of the herd is ideal, but unlikely.
Rich nations have reserved most of the vaccines that will be manufactured this year. In the United States, for example, officials said enough people could be vaccinated by the fall to begin to return to normal.
But many poorer countries will probably have to wait longer. That is why the World Health Organization has warned that the global immunity of the herd is unlikely to be reached this year.
Differences in vaccination levels between countries are also the reason why many experts believe that the virus will never be completely eliminated.
CAN THE IMMUNITY OF LOSS BE DONE?
It is not known how long immunity lasts, either after vaccination or after an infection, although experts believe it should be at least a few months old.
However, booster photos on the road may be required. And, although current COVID-19 vaccines are expected to work on variants identified in the UK and elsewhere, the virus may move sufficiently over time, so vaccines should be updated.
Influenza virus mutations, for example, are why we get flu shots every year. But experts note that coronaviruses do not move as easily.
WHAT IF COVID-19 VACCINES DO NOT PREVENT INFECTION?
The current COVID-19 vaccines seem to be very effective in preventing people from getting sick. We don’t know yet how good they are to stop the infection altogether, but it should help reduce the spread of the virus.
This is because vaccines stop the virus from multiplying in your body. So, even if you get infected after vaccination, your body should shed fewer viruses for a shorter period of time, said Deborah Fuller, a vaccine expert at the University of Washington.
It is another reason why vaccinating as many people as possible is essential to ending the pandemic.
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