Herd immunity can be achieved when most of a population is immune to an infectious disease, providing indirect protection or herd protection to those who are not immune to the disease.
Two ways can provide herd immunity, according to experts – when a large proportion of the population gets infected or gets a protective vaccine.
Now, the World Health Organization (WHO) says that the world is nowhere near the amount of coronavirus immunity needed to induce herd immunity, where enough people would develop the antibodies to stop the spread of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).
What is herd immunity?
Herd immunity or community immunity happens when a high percentage of a certain community is immune to a disease, either through prior illness or vaccination, making the disease spread from one person to another unlikely.
Image Credit: Paolo De Gasperis / Shutterstock
People who cannot receive the vaccine due to a weakened immune system, pregnant women or newborns, are offered some protection because the disease has little opportunity to spread. The concept of herd immunity is to protect the most vulnerable members of the population, and if enough people receive the vaccine, those who are susceptible to developing severe illness are protected as well.
Herd immunity is usually achieved with vaccination, and most health experts estimate at about 60 to 70 percent of the population should develop antibodies to prevent an outbreak. A recent study published in the journal Science reveals that herd immunity against SARS-CoV-2, the virus that causes the coronavirus disease (COVID-19) can be achieved at a population-wide infection rate of 40 percent, which is considerably lower than previous estimates.
"This shift is because transmission and immunity are concentrated among the most active members of a population, who are often younger and less vulnerable. If nonpharmaceutical interventions are rigorous, no herd immunity is achieved, and infections will then resurge if they are eased too quickly," the researchers noted in the paper.
Nowhere near herd immunity
The executive director of WHO's Health Emergencies Program, Mike Ryan, said the world is nowhere near herd immunity after some experts said that community protection could be attained if 40 percent of people developed antibodies against COVID-19.
"I think what we can say with certainty is, right now, as a planet, as a global population, we are nowhere close to the levels of immunity required to stop this disease transmitting. And we need to focus on what we can actually do now to suppress transmission and not live in the hope of herd immunity being our salvation. Right now, that is not a solution."
Early in the pandemic, the United Kingdom was one of the countries who pondered herd immunity as a health strategy to stop the spread of the virus. However, the government received a backlash on the strategy, and amid the pandemic, issued lockdowns orders when the infection rate steadily increased.
Sweden, on the other hand, continued with its herd immunity strategy and avoided locking down the country. Health experts in the country said that a lockdown is not the solution to the virus spread since it only delays it.
In another study published on the open-source medRxiv*, comparing England's lockdown vs. Sweden's herd immunity approach to COVID-19, the researchers noted that the lockdown approach is recommended and an effective way to reduce the speed and extent of infections in a country.
Opting for herd immunity is dangerous and could kill a lot of people, WHO experts warned.
Vaccine is the only solution
Being exposed to the virus is a way to develop protection, which can induce the production of antibodies that can fight the virus. However, experts said that they do not know how strong and long the protection is.
The more effective way to protect the population against the coronavirus, and induce herd immunity is to get a vaccine. However, a safe and effective vaccine is not yet available, but six vaccines are underway as they continue with the last phase of clinical trials.
The WHO also emphasizes that while the world is waiting for the approval of a COVID-19 vaccine, the most effective strategies countries should implement include testing, contact-tracing, isolating, mask-wearing, proper hand hygiene, and physical distancing.