Herd Immunity Can Be Confusing
Technically what herd immunity means is, depending on the level of transmissibility of an infectious agent, if enough people become infected and recoverand therefore are partially immuneor if they get vaccinated, it means that that will diminish, reduce or even halt virus transmission in the community, Dr. Hotez explained.
Herd immunity is a confusing topic because its different for different things, said Dr. Liddell. But the general idea of herd immunity is that you have protection in a community.
Even though a person may not have immunity for whatever reasonmaybe they don’t have a strong immune system, they’re unable to get the vaccine or children are the obvious example right nowwhat we do is we surround them, he said. We insulate them from the virus by having everybody around them have immunity.
The best example is measles. Measles is one of the most transmissible agents, said Dr. Hotez. We know it has a reproductive number of between 12 and 18, and what that means is if you have over 90% of the population immuneeither because of infection or vaccinationit can halt transmission. This has been more or less the situation for the last two decades in the U.S, until measles transmission resumed in 2019 due to local declines in immunization rates due to antivaccine targeting of parents.
The Indirect Effects Of Herd Immunity
Among vaccine experts, the term community immunity is preferred over herd immunity, says Dr. Omer. Population immunity is another term commonly used.;
But they all have the same meaningand include the indirect benefit of protecting vulnerable groups. For example, some people have medical conditionsor are undergoing specific cancer treatmentsthat cause them to produce few or no antibodies in response to a vaccine. With herd immunity reducing spread of the virus in a vulnerable persons community, they are protected by default.;
We increase vaccine coverage and thereby decrease disease transmission, Dr. Omer says. That way, people who are not vaccinated are also protected indirectly, because there’s less virus to go around.
Dr. Juthani notes that the indirect benefits of mass vaccination are sometimes invisible to the general public.
But reframing the way you think about herd immunity might be helpful, she adds. If you think of your extended family as your herd, it may better illustrate the concept of protection, she says. Knowing that everyone getting vaccinatedand not harboring any viruscan protect, for example, a grandparent with cancer or a cousin who is immuno-compromised, can make the benefits of getting vaccinated feel less abstract and more tangible.;
That mindset is important, adds Dr. Omer. We will see an increase in the indirect, or community, effects of vaccines as the rates of vaccination go up.
Herd Immunity And Covid
Typically, you need a fairly high vaccination rate to achieve herd immunity, and COVID-19 is no exception.
While its too soon to say exactly what percentage of people need to have immunity, either from getting the disease or from a vaccine, the World Health Organization says the number is substantial.
Dr. Piedra estimates it to be higher than 80 to 85 per cent of the population.
Some people, including politicians, have suggested that we should let the virus run its course through communities and gain immunity that way. The proposal boils down to letting the virus infect a whole bunch of people so the population at large can reach herd immunity faster.
Both Swann and Dr. Piedra disagree with that approach.
This really puts many people at huge risk, says Dr. Piedra. If you think about before vaccines became available, that approach is what has caused all the deaths and hospitalizations that have occurred worldwide.
Read Also: Which Covid Vaccine Is Cvs Using
Its Unclear Whether Vaccines Prevent Transmission
The key to herd immunity is that, even if a person becomes infected, there are too few susceptible hosts around to maintain transmission those who have been vaccinated or have already had the infection cannot contract and spread the virus. The COVID-19 vaccines developed by Moderna and PfizerBioNTech, for example, are extremely effective at preventing symptomatic disease, but it is still unclear whether they protect people from becoming infected, or from spreading the virus to others. That poses a problem for herd immunity.
Herd immunity is only relevant if we have a transmission-blocking vaccine. If we dont, then the only way to get herd immunity in the population is to give everyone the vaccine, says Shweta Bansal, a mathematical biologist at Georgetown University in Washington DC. Vaccine effectiveness for halting transmission needs to be pretty darn high for herd immunity to matter, she says, and at the moment, the data arent conclusive. The Moderna and Pfizer data look quite encouraging, she says, but exactly how well these and other vaccines stop people from transmitting the virus will have big implications.
What’s Standing In The Way Of Herd Immunity From Covid
Early on in the pandemic, a report from the Center for Infectious Disease Research and Policy at the University of Minnesota estimated that, in order for the U.S. to achieve herd immunity against COVID-19, roughly 60 to 70 percent of the population would need to be immune to the virus whether from being vaccinated or from developing antibodies as a result of being infected with the virus. However, in a recent WBUR interview, Anthony Fauci, M.D., director of the U.S. National Institute of Allergy and Infectious Diseases, estimated that figure as more like 70 to 80-plus percent.
But now, those initial projections don’t really hold up, says Mathema. “, we are now unlikely to reach herd immunity,” he says. This is due to three main factors: 1) new strains of COVID-19 are emerging with mutated characteristics and rates of infectiousness 2) a significant percentage of people in the U.S. are refusing to get the vaccine, and 3) global vaccination and mitigation efforts have been particularly messy.
Don’t Miss: Is It Safe To Drink Alcohol After Covid Vaccine
Can Covid Vaccines Stop Transmission Scientists Race To Find Answers
Vaccines that can block viral transmission will help control the pandemic.Credit: Andrea Fasani/EPA-EFE/Shutterstock
As countries roll out vaccines that prevent COVID-19, studies are under way to determine whether shots can also stop people from getting infected and passing on the SARS-CoV-2 virus. Vaccines that prevent transmission could help to bring the pandemic under control if they are given to enough people.
Preliminary analyses suggest that at least some vaccines are likely to have a transmission-blocking effect. But confirming that effect and how strong it will be is tricky because a drop in infections in a given region might be explained by other factors, such as lockdowns and behaviour changes. Not only that, the virus can spread from asymptomatic carriers, which makes it hard to detect those infections.
These are among the hardest types of studies to do, says Marc Lipsitch, an infectious-disease epidemiologist at the Harvard T. H. Chan School of Public Health in Boston, Massachusetts. All of us are out there, hungrily trying to see what we can get out of little bits of data that do come out, he says. Results from some studies are expected in the next few weeks.
What Are Vaccine Makers Doing
Like Moderna, other coronavirus vaccine makers have said that they are looking into updating their vaccines. They include Johnson & Johnson of New Brunswick, New Jersey, which is developing a single-shot coronavirus vaccine.
Some aspiring vaccine makers have had their eye on the threat that escape variants might pose from the start. A team at Gritstone Oncology decided to focus on this potential problem by designing a vaccine that targets multiple sites on several viral proteins, in contrast to first-generation shots that target only the spike protein, says Andrew Allen, president of the company in Emeryville, California. The hope is that the vaccine, which should soon start clinical trials, will make it difficult for the virus to evade immunity because many genetic changes would be necessary for it to do so. You can either play whack-a-mole and chase the variants, or you can try to get ahead of them, Allen says.
Because updating the construction of exisiting vaccines is relatively simple, a new RNA vaccine could be designed and manufactured for clinical testing within six weeks, Weissman estimates.
But that is only the beginning. Mass-producing a vaccine is hard. To start all over again will be hard, says Offit.
Also Check: Is It Possible To Be Immune To Covid
What Was Said In Public About Herd Immunity
The person at the forefront of the public debate over herd immunity was the government’s chief scientific adviser, Sir Patrick Vallance.
On 9 and 12 March he appeared alongside the prime minister in Downing Street.
Although he did not mention herd immunity explicitly, he said we shouldn’t suppress the virus “completely”, otherwise it would return later in the year: “It’s not possible to stop everybody getting it and it’s also actually not desirable, because you want some immunity in the population, we need to have immunity to protect ourselves in the future.”
On 13 March, he explicitly mentioned herd immunity, telling BBC Radio 4’s Today programme it was beneficial “to build up some degree of herd immunity so more people are immune to this disease”.
The same day he appeared on Sky News, claiming about 60% of the population would need to contract the virus to achieve herd immunity.
Other government advisers were making similar arguments. On 11 March, David Halpern, who runs the Behavioural Insights Team, said it would be right to “cocoon” those most at risk in society, and once they had emerged from isolation, “herd immunity has been achieved in the rest of the population”.
The prime minister appeared on ITV’s This Morning on 5 March. Boris Johnson said one of the “theories” was to “take it on the chin, take it all in one go and allow the disease, as it were, to move through the population, without taking as many draconian measures”.
Is It Possible To Achieve Covid
- A population is said to achieve herd immunity when a large percentage of individuals become immune to a disease. A doctor on whether or not we will get there anytime soon.
Amid the fear of third wave of Covid-19 infection and a surge in Delta cases in Maharashtra, India continues its fight against the deadly infection with all its might as the country’s vaccination drive is on in full steam.;
According to reports, India on Sunday registered 42,766 new cases of coronavirus disease in the last 24 hours taking the active caseload to 4,10,048 comprising 1.24 per cent of the total infections.;
Out of nearly 11 variants of SARS-CoV-2 virus being monitored by WHO, Delta Plus also known as B.1.617.2.1 or AY.1 is on rise in India as well other parts of the world. Towards the end of August, Maharashtra recorded 103 Delta Plus cases. Approximately 65% of the reported cases were amongst the unvaccinated population.;
Dr Rahul Pandit, Director-Critical Care, Fortis Hospitals Mumbai & Member-Maharashtra COVID19 Taskforce explains more about how a virus mutates and what is the possibility of achieving herd immunity against it.
What happens when a virus mutates
How and when will we achieve herd immunity?
Can herd immunity reduce the chance of transmissibility?
Vaccination is the way forward;
Follow more stories on &
Recommended Reading: Is Cvs Giving Covid Vaccine
Will It Ever End
Many scientists;have been;pessimistic;from the start;about the chances of;us reaching the herd immunity threshold and eradicating Covid-19, even with the;swift development of effective vaccines.
Professor Paul Hunter from the University of East Anglia said: Our grandchildrens grandchildren will be getting the infection. Looking at the other coronaviruses, we can expect to get repeat infections every four to six;years, probably more frequently this decade.
But dont despair. We know that second infections and;infections;after immunization are usually less severe than first infections,;so;the vast majority of;these infections will be asymptomatic or mild common cold.
Professor Willem van Schaik from Birmingham University told;FactCheck: The focus on herd immunity has been somewhat confused from the start of the pandemic as the underlying assumption of herd immunity claims was that those that had antibodies to SARS-CoV-2, either through vaccination or prior infection, would be entirely protected from re-infection and would no longer transmit the virus.
This is true for a number of infectious diseases but SARS-CoV-2 is a different type of virus that can still infect people that have antibodies. Importantly, upon infection symptoms will be generally mild in these individuals but they will still be able to transmit the virus.
Immunity Might Not Last Forever
Calculations for herd immunity consider two sources of individual immunity vaccines and natural infection. People who have been infected with SARS-CoV-2 seem to develop some immunity to the virus, but how long that lasts remains a question, Bansal says. Given whats known about other coronaviruses and the preliminary evidence for SARS-CoV-2, it seems that infection-associated immunity wanes over time, so that needs to be factored in to calculations. Were still lacking conclusive data on waning immunity, but we do know its not zero and not 100, Bansal says.
Modellers wont be able to count everybody whos been infected when calculating how close a population has come to the herd-immunity threshold. And theyll have to account for the fact that the vaccines are not 100% effective. If infection-based immunity lasts only for something like months, that provides a tight deadline for delivering vaccines. It will also be important to understand how long vaccine-based immunity lasts, and whether boosters are necessary over time. For both these reasons, COVID-19 could become like the flu.
Read Also: Can A 14 Year Old Get The Covid Vaccine
How Do You Achieve Herd Immunity
There are two ways this can happen.
You can develop resistance naturally. When your body is exposed to a virus or bacteria, it makes antibodies to fight off the infection. When you recover, your body keeps these antibodies. Your body will defend against another infection. This is what stopped the Zika virus outbreak in Brazil. Two years after the outbreak began, 63% of the population had had exposure to the virus. Researchers think the community reached the right level for herd immunity.
Vaccines can also build resistance. They make your body think a virus or bacteria has infected it. You dont get sick, but your immune system still makes protective antibodies. The next time your body meets that bacteria or virus, its ready to fight it off. This is what stopped polio in the United States.
When does a community reach herd immunity? It depends on the reproduction number, or R0. The R0 tells you the average number of people that a single person with the virus can infect if those people arent already immune. The higher the R0, the more people need to be resistant to reach herd immunity.
Researchers think that the R0 for COVID-19 is between 2 and 3. This means that one person can infect two to three other people. It also means 50% to 67% of the population would need to be resistant before herd immunity kicks in and the infection rates start to go down.
Vaccines Might Change Human Behaviour
At current vaccination rates, Israel is closing in on the theoretical herd-immunity threshold, Aran says. The problem is that, as more people are vaccinated, they will increase their interactions, and that changes the herd-immunity equation, which relies in part on how many people are being exposed to the virus. The vaccine is not bulletproof, he says. Imagine that a vaccine offers 90% protection: If before the vaccine you met at most one person, and now with vaccines you meet ten people, youre back to square one.
Recommended Reading: When Can We Get Covid Vaccine
With Herd Immunity Elusive Vaccination Best Defense Against Covid
Epidemiology expert Julie Parsonnet warns that COVID-19 vaccine hesitancy has probably made herd immunity unattainable, which makes vaccination all the more important for personal health.
A focus on vaccinations rather than on herd immunity will help protect more people, epidemiologist Julie Parsonnet says.oxinoxi/Shutterstock.com
COVID-19 vaccinations are now readily available to all Americans, so herd immunity should be attainable, right?
Probably not, says , MD, professor of medicine and of epidemiology and population health. Paradoxically, it may be the very concept of herd immunity that is thwarting the uptake of vaccinations in the United States.
We need to stop pushing herd immunity to the public, Parsonnet said, as it may discourage some people from getting vaccinated in the mistaken belief that, if other people get vaccinated, they can just wait for herd immunity. Public health departments dont talk about herd immunity because its not helpful for the immediate protection of individuals and the overall response to the pandemic. Whats important is getting as many people vaccinated as you possibly can.
What Is Herd Immunity
Put simply, herd immunity relates to the idea that a high level of immunity to a virus in a population can be achieved by both natural infection and by vaccination.
The latter method is preferred as vaccines overwhelmingly create immunity without causing illness or adverse health complications, unlike the natural infection route.
The antibodies procured by natural infection and vaccination usually protect against future infection. If enough people in a population are immune this leads to lower rates of prevalence of disease or viruses in a community. If a virus has less opportunity to spread and infect, it can be greatly controlled or even eradicated.
With herd immunity, those who are not vaccinated are protected by the overall level of immunity present in a population.
Mass, successful vaccination programs have meant deadly, contagious viruses and diseases such as polio, tuberculosis and measles have been largely eradicated in parts of the world or greatly suppressed by vaccination programs and the herd immunity they foster.
Recommended Reading: How Long Does The Covid Shot Last