Thursday, March 23, 2023

What Impact Does Reduced Vaccination Have On Herd Immunity

At Least 85% Need To Be Vaccinated

How does herd immunity work?

What we need to do is we need to get 85% of the U.S. population vaccinatedwe need all of the adolescents and all of the adults, said Dr. Hotez, noting that except for a few areas in the Northeast and maybe Pacific Northwest, it’s not happening.

In fact, the opposite’s happening in the South and that’s why we’re seeing Delta rage through the South right now, he added. Its going to be really problematic to get through a school year safely in many parts of the South unless we can fix these vaccination rates.

The Simple Math Of Herd Immunity

When a new infection enters a fully susceptible population, as SARS-CoV-2 infection did in early 2020, each infectious case on average infects R0 other cases. As the disease spreads, it leaves in its wake immunity to infection in some or all of those who have recovered. Moreover, once society recognizes the threat, measures can be put in place that may further hamper spread. At some time t when the disease has been spreading for a while, the average case in a population will infect R others in that population, where usually R< R0, thanks to the combined effect of immunity to infection that has accumulated, and control measures. As has become common knowledge thanks to the teachable moments of this pandemic, when each individual infects on average more than one other, the number of cases will rise, and when each individual infects on average less than one other, the number of cases will fall.

Uncertainty In X Part 2

The efficacy of vaccines against SARS-CoV-2 has been measured very rapidly, with the consequence that most of the data come from a period very shortly post vaccination. It is completely normal for vaccination to produce antibody concentrations that decline with time, rapidly over months and then more slowly over years , sometimes with a concomitant decline in protection. In other vaccines, the antibody concentration needed to protect in the nasopharynx is higher than that needed to prevent disease . So it is possible that all of the vaccine efficacy measures, including those against transmission, will decline with time since vaccination.

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Institutional Review Board Review

The protocol was reviewed by the Stanford University School of Medicine Committee on the Protection of Human Subjects and approved as exempt. Each participant provided consent on three occasions. In addition to the two YouGov consents, participants were presented with a Stanford consent form, and all provided electronic consent.

Which Group Was Vaccinated First

Vaccine Information

Another interesting indicator is which group of people each country chose to give the first COVID-19 vaccine to.

Countries in our study are split equally between healthcare professionals and the elderly.

There is also a handful of countries, like Turkey, Serbia, the Czech Republic and Bulgaria that chose to give it to politicians first. In some instances, this could be a way of trying to allay the fears of a vaccine-sceptic population.

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Herd Immunity Won’t Come Easy Though

Like most things pandemic-related, herd immunity comes with a question mark or two.

“In particular, we don’t yet know how long vaccine-induced immunity will last. The natural immunity acquired after infection seems to last for several months, and the expectation is that the immunity conferred via vaccination will last even longer. But we don’t know exactly how long yet,” explains Dr. Drews. “This is one of the major reasons that it will be important to continue wearing a mask after being vaccinated, as well as practicing the other preventive measures we’ve used to keep our communities safe during this pandemic.”

And it’s not just questions, there are challenges, too.

“There are logistical hurdles to vaccinating 248+ million people. In addition, many people are still skeptical about these vaccines, and misinformation is adding to this fear,” says Dr. Drews.

But, with Delta variant cases on the rise especially among the unvaccinated it’s time for the entire herd to come together to help to end this pandemic by getting vaccinated.

Remember, to this virus, there are no sqauds, no crews, no pods only one big herd. And herd immunity, by way of vaccination, is what we need to help keep our squads, crews, pods and fams safe.

Herd Immunity For Covid

Scientists are currently working on a vaccine for SARS-CoV-2. If we have a vaccine, we may be able to develop herd immunity against this virus in the future. This would mean getting the SARS-CoV-2 in specific doses and making sure the majority of the worlds population is vaccinated.

Almost all healthy adults, teens, and older children would need to be vaccinated to provide herd immunity for people who cant get the vaccine or who are too ill to become naturally immune to it.

If youre vaccinated and build immunity against SARS-CoV-2, you most likely wouldnt contract the virus or transmit it.

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Vaccines And Herd Immunity

Countries that have begun distributing COVID-19 vaccines soon expect to see a reduction in severe illness. But it will take longer to see how effectively vaccines can reduce transmission. Data from clinical trials suggest that vaccines that prevent symptomatic infection might also stop a person from passing on the virus.

If vaccines do block transmission and if they remain effective against newer variants of the virus it might be possible to eliminate the virus in regions where enough people are vaccinated so that they can protect those who are not, contributing to herd immunity. A vaccine that is 90% effective at blocking transmission will need to reach at least 55% of the population to achieve temporary herd immunity as long as some social distancing measures such as face masks and many people working from home remain in place to keep transmission in check, according to a model developed by Alexandra Hogan at Imperial College London and her colleagues. But if the rate of transmission increases because of a new variant, or if a vaccine is less effective than 90% at blocking transmission, vaccine coverage will need to be greater to blunt circulation.

Vaccinating even 55% of the population will be challenging in many countries. The virus will stick around if parts of the world dont get vaccinated, says Jeffrey Shaman, an infectious-disease researcher at Columbia University in New York City.

How Many People Need To Get Vaccinated

Coronavirus Q& A: Impact of different vaccines on herd immunity

Herd immunity looks different for different viruses. That’s because the concept hinges on how easily a particular virus spreads from person to person.

“It’s still unclear exactly how many people will need to be vaccinated in order to achieve herd immunity to COVID-19, but experts estimate that it will take at least 70% of the population with some estimates ranging as high as 90%,” says Dr. Drews.

In the U.S., that means at least 248 million people will need to be vaccinated.

“What we need to keep in mind is that some people can’t get vaccinated, either due to their age or medical history. So those of us who can get vaccinated need to do our part to protect those who can’t,” explains Dr. Drews.

Lastly, if you’ve already had COVID-19, don’t assume this means that you don’t need to get vaccinated. It’s important to know that you can get COVID-19 more than once meaning vaccination is still important for you, too.

So, even if you’re young and healthy and even if you’ve had COVID-19 and recovered, here’s why herd immunity is so necessary.

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Why Should People Get Vaccinated Against Flu

Influenza is a potentially serious disease that can lead to hospitalization and sometimes even death. Every flu season is different, and influenza can affect people differently, but millions of people get flu every year, hundreds of thousands of people are hospitalized and thousands to tens of thousands of people die from flu-related causes every year. Flu can mean a few days of feeling bad and missing work or it can result in more serious illness. Complications of flu can include bacterial pneumonia, ear infections, sinus infections and worsening of chronic medical conditions, such as congestive heart failure, asthma, or diabetes. An annual seasonal flu vaccine is the best way to help protect against flu. Vaccination has been shown to have many benefits including reducing the risk of flu illnesses, hospitalizations and even the risk of flu-related death in children. While some people who get a flu vaccine may still get sick, flu vaccination has been shown in several studies to reduce severity of illness.

Herd Immunity: An Explanation

Put simply, herd immunity means a large portion of a community is immune to a disease, making further disease spread unlikely. Immunity is conferred either by building antibodies after an infection from the virus or from a vaccine.

Ellen Foxman, MD, PhD, a Yale Medicine pathologist who is an expert in respiratory viruses, likens herd immunity to making the virus hit a dead end.

If you are coughing and sneezing, and the droplets reach someone who is susceptible, then the virus will keep spreading, Dr. Foxman says. But if the virus reaches someone who has immunity, it is like hitting a wall. The virus cant go any further.

We need to get vaccinated as soon as we can so we can prevent the spread of COVID-19, which will also prevent the emergence of variants. Its a race between vaccination and variants.Ellen Foxman, MD, PhD, a Yale Medicine pathologist

The percentage of the population that needs to be immune to attain herd immunity varies by disease and how contagious that disease is. Measles, for example, spreads so easily that an estimated 95% of a population needs to be vaccinated to achieve herd immunity. In turn, the remaining 5% have protection because, at 95% coverage, measles will no longer spread. For polio, the threshold is about 80%.

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Herd Immunity Is Powerful And It Takes Well The Herd

To understand herd immunity, let’s take a look at our squads, our crew, our pods, our fams because, whether we’ve realized it yet or not, these groups have blended together to create one big herd during this pandemic.

Let’s say your squad is five of your old college buddies. Three of you are taking the pandemic pretty seriously, but the other two aren’t. After what you thought was a safe gathering, three of you end up with COVID-19 presumably via your friend who’s being less safe, but in this fake scenario there’s no need to point fingers. You’re all young and healthy, and your mild cases aren’t fun by any stretch of the imagination, but they’re not life-threatening.

But, one of your friends in your squad also has a crew the three friends he plays golf with on weekends. And before he even realizes he’s sick, his crew gets sick, too. Fortunately, only mild cases in the crew, too.

Except, someone in the crew has a wife who is high risk. Unfortunately, she gets COVID-19 and her case is severe.

The fact is that, right now, your squad isn’t just your five friends. Your squad is also the three people in someone else’s crew, the 10 people in another person’s pod, as well as your family and their own squads, crews and pods. It’s also your coworkers, the teachers at your kids’ schools and the random people you encounter running errands.

There are no squads, crews and pods during this pandemic, only the herd.

Think Global Act Local

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Dr. Juthani says she believes herd immunity can be achieved, but that it may take several years.

We need to get the rest of the world vaccinated, and that is happening more slowly than we would like, she says. The current outbreak in India is also putting a wrench in global vaccination plans since many vaccines are mass produced in India.

While the vaccination pace in the U.S. has been swift, that is not the case worldwide. As of May 2, 43.9% of the U.S. population have had at least one vaccine dose and 30.9% are fully vaccinated. Worldwide, only 3.5% are fully vaccinated.

There are several reasons to be concerned about COVID in other countries, Dr. Omer says, even if we think it doesnt directly affect us.

There is a responsibility that comes with the resources that each country has. We will be judged by our children and grandchildren in terms of how we behaved in this pandemic, he says, noting that what is happening in India and in other places, is happening on our watch. We are privileged to live in a country where these vaccines are available. Everyone should go out and get it.

And, there is also the case of enlightened self-interest, Dr. Omer adds.

Right now, the dam is holding, he says. But why test the dam by tempting it with these large tidal waves coming through?

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Immunity May Not Be Permanent

Immunity against any disease only lasts as long as our bodies retain immune memorythe ability to recognize an antigen and reinitiate an immune response.

Polio vaccinations, for example, protect for many years. This, combined with widespread vaccination coverage, has brought the world close to eradicating the disease. Others, like influenza vaccination, must be administered every year.

A recent study found that natural immunityfrom previous infectionto COVID-19 can last at least eight months. Its still too early to tell how long immunity from vaccination will last. If it isnt long-lasting, its possible that vaccinations against SARS-CoV-2 might be needed annually, like the influenza vaccine.

Were going to have to continue to monitor, Dr. Marfin says. But in the meantime, keep wearing your masks.

Minimizing The Impact On Family

The economic impact of adult illness is evident from loss of productivity and pay for the duration of the illness and recovery period. The impact of childhood illness falls primarily on their adult carers, generally parents. In most industrialized regions, two-parent families are reliant on both parents undertaking at least part-time or full-time work. Therefore, when a child is unwell with childhood illnesses, which may or may not necessitate admission to hospital, the parent will invariably have to forego their paid employment to care for the child. In seven European countries one parent or carer required time off work in 3991% of rotavirus gastroenteritis cases . This loss of productivity in the parental workforce tends to disproportionately affect women, but loss of either parental attendance at work reduces overall employer productivity and in the short-term is rarely replaced. This argument was made for the impact of chicken pox on children, whereby the exclusion from school mandates parental caring at home for a period until the lesions are crusted over. VZV vaccines are estimated to have had a similar impact as rotavirus vaccine in United States studies . In many regions, mothers are still the primary carers, spending their days at home caring for children and maintaining the household in these settings, the impact on this unpaid work is harder to determine.

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Herd Immunity And Introduction Strategies

Protection against the bacterial meningitis pathogens through herd immunity is a remarkable, powerful, and unanticipated effect of bacterial polysaccharide-protein conjugate vaccines.35 Herd immunity can account for approximately one half of their effectiveness at preventing disease and has significantly enhanced their cost-effectiveness. It is an important strategy for vaccine introduction, implementation, and evaluation. As noted, in 1999 to 2000 the meningococcal serogroup C conjugate vaccines were introduced in the United Kingdom as a broad catch-up campaign for those younger than 19 years of age, reduced nasopharyngeal carriage of serogroup C in adolescents more than 75%, and created herd immunity that has persisted for more than a decade.413,417 The explanation for this remarkable herd immunity effect is the low R0 , estimated at 1.3, for meningococcal disease providing herd immunity with 17% to 26% vaccine coverage of the population.35,434 In contrast, measles, mumps, pertussis, polio, and rubella have an R0 greater than 5 and require much higher thresholds .427 The immunologic basis of mucosal immunity with conjugate vaccines remains unclear. Generation of capsule-specific mucosal immunoglobulins, transudation of high-avidity serum IgG to mucosal surfaces, and Th17-induced immunity via macrophage clearance have been proposed.35

What We Are Still Learning

Variants and ‘Vaccine deserts’ impede herd immunity
  • How well the vaccines protect people with weakened immune systems, including people who take medicines that suppress the immune system
  • How long COVID-19 vaccines protect people
  • How many people have to be vaccinated against COVID-19 before the population can be considered protected
  • How effective the vaccines are against new variants of the virus that causes COVID-19

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Herd Immunity And The Flu

Some vaccines are better at producing herd immunity than others. The measles, mumps, and rubella vaccine is 97% effective at preventing measles. So when lots of people in a community get this vaccine, protection rates stay high.

The flu vaccine is a little different. It’s only about 40% to 60% effective in any given year. That’s because sometimes the virus strains in the vaccine don’t exactly match the virus that spreads.

Even if the flu vaccine isn’t perfect, it’s still worth getting, Brady says. In any one flu season, the flu vaccine prevents millions of people from getting the flu. “That’s particularly important when the people who don’t get the flu are around people who are over 65, or have , or are young,” he adds.

The flu vaccine is also good at protecting small groups of people — such as in your home, office, or school. When you get vaccinated, you help an older adult relative who has a chronic disease, or a baby who is too young to get vaccinated avoid getting sick, Cohn says.

Vaccines are especially important for people who work in hospitals and other health care centers. The sick people they care for are more likely to get flu complications, and they need more protection.

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