So I “Herd” Something about Immunity: COVID-19

February 15, 2021

So I “Herd” Something about Immunity: COVID-19

There has been a lot of talk recently about COVID-19 vaccinations and the end of the pandemic. But how does this really work? How do vaccines help with this?

What Protections Do Vaccines Provide?

If a person receives a vaccine, and the vaccine is effective, they are generally protected (at least for a time) from becoming ill with that infection. We’re used to getting vaccines all the time: flu vaccines in the fall, tetanus vaccines every few years or after an injury, and childhood vaccines against a bunch of different infections. While these vaccines will help protect the person getting the vaccine, they will also usually help protect those who have not been vaccinated.

For something like tetanus, which you can get from the old rusty metal injury, one person having the vaccine will not help somebody else. If the person with the injury has the vaccine, they should be good. If they have not had the vaccine, they are at risk of tetanus. Infections that spread from person-to-person, however, are different.

For an infection that passes from person-to-person, vaccines can help protect others in the community. This is called “herd immunity.” In order for the infections to continue to exist, they have to have people to infect. If each person who is infected ends up infecting one other person, the level of disease in the community is stable. If each infected person (on average) ends up infecting more than one person, the amount of sick people in the community increases. And finally, if each infected person ends up infecting less than one person, the disease will eventually go away or to very minimal levels. Obviously, an ill person cannot infect half of another person, but the numbers work out when you’re dealing with many people in the population.

What is “Herd Immunity?”

This is where vaccines help. If you have not gotten a vaccine, but you are hanging around with one hundred people who have all gotten the vaccine, they are less likely to be able to get sick and spread the infection to you. So, you end up protected even though you haven’t gotten the vaccine yourself. This is called “herd immunity.” It was first recognized in the early 1900s when it was noticed that after many kids in an area had measles, the rate of measles infection went down even in kids who had not become ill. While this natural infection helped, there wasn’t a huge reduction in the rate of measles until mass vaccinations began for measles in the 1960s. Currently, because of vaccination, almost all of the measles cases in the United States are either in travelers from overseas or in groups of people who have not received vaccination. Unlike the large spread of measles before widespread vaccination, current outbreaks tend to be relatively small and tend to burn out pretty quickly.

It is hoped that COVID-19 will act the same way. If many people in the country are immune to the disease, there will be fewer people who can be infected and spread will really slow down. But enough people need to be vaccinated in order for this to work. The problem is that the more contagious an infection is, the more people overall need to be vaccinated in order to reach the level of true herd immunity. How many people need to be vaccinated or immune from natural infection for this to work? That’s where there are many questions.

How Do Variants Affect Herd Immunity?

There have been identified several new variants of COVID-19 that seem to be more easily spread between people. This means that a larger amount of people in the population will need to be vaccinated or otherwise immune in order to quash the spread of virus. There are other things that need to be considered too. Not all people in the population are as likely to spread an infection. For example, someone who works as a cashier in a grocery store or driving a bus is much more likely to be infected or spread infection than someone who never leaves the house. Also, even though it is likely that a vaccinated person is less likely to be able to asymptomatically spread infection, we’re not yet sure how much this is decreased. Because of these uncertainties, we don’t know exactly how many people need to be vaccinated for herd immunity in the United States. The best guess for now is somewhere between 70%-85% of the population. With the two vaccines currently available, two shots are needed for each person, so even though about 1.5 million doses are given each day in the United States, it’s going to take quite some time for everyone who wants vaccine to receive one.

Are the COVID-19 Vaccines Safe?

In general, yes, they are safe. There have been some reports of allergic reactions, and even fewer reports of unusual reactions after receiving vaccine. It is not uncommon to have a reaction like fever or muscle aches; this is just your immune system doing its job and learning how to respond to the virus. My opinion on safety: I enrolled in the Moderna vaccine trial last fall, and received the vaccine in August 2020. Although when I signed up, I didn’t know if I would receive the vaccine or placebo, it turns out I got the vaccine. I trusted the vaccine enough, based on what I read, to allow my own body to research how well it worked. Even more telling: my 14 year old son is enrolled in the Pfizer vaccine trial that is currently in progress for kids.

Having questions about a vaccine that was developed faster than any other in history is reasonable and fair. My best advice on this: ask your primary health provider any questions that you have about your health and vaccine. I realize that this is a blog post, which makes the following statement somewhat ironic: don’t necessarily believe what you read on the internet, or Facebook, or twitter, or Instagram, or whatever platform of your choice when it comes to your health. If you have questions, talk to your health provider so that you can decide what is best for you.

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