Little more than a year ago, not one of us had heard of the COVID-19 coronavirus strain. And not one of us was definitively immune. 

In the months that followed, the COVID pandemic wreaked havoc across families and neighborhoods and around the globe, stealing our loved ones, confining us to our homes, ravaging businesses and bringing the freedom- and activity-rich lives to which we’d become accustomed to a halt. So in early December, as news of effective vaccines against the virus reached the public and those precious vials began to make their way across America, even the most skeptical among us entertained the thought of life finally, finally returning to normal. Or at least normal-ish.

For most of us, however, the idea of “herd immunity” — protection for both those who receive the injection and those who eschew — offered by mass vaccination against a brand new virus is unfamiliar territory. Are the new vaccines safe in the long term? If we’ve already had COVID, do we need to receive them? Do they also cover new and emerging mutations? Once we’ve been vaccinated, are we safe to move unfettered through the world?


MKE Lifestyle asked Laura Cassidy, PhD, epidemiologist at the Medical College of Wisconsin, for some insight on the realities of herd immunity and realistic expectations for the future.

Most of us have heard of herd immunity, but what is the “official” definition?

Cassidy: According to the World Health Organization (WHO), “herd immunity” — also known as “population immunity” — is the indirect protection from an infectious disease that happens when a population is immune either through vaccination or immunity developed through previous infection.

Basically, when we get enough people vaccinated, it is difficult for a disease to take hold and spread in a community. Importantly, with COVID-19, we want to work to achieve immunity through vaccination, not infection. 

Does the medical community have hope that herd immunity might begin to gain momentum as we head into spring and summer? Summer and fall?

Cassidy: To safely achieve herd immunity against COVID-19, a substantial percentage of a population needs to be vaccinated, which in turn decreases the number of people who can spread the virus in the population. Experts suggest that the United States could achieve herd immunity against COVID-19 by the end of the second quarter 2021 after vaccines are widely available. However, this also depends upon people’s willingness to take the vaccine.

As more and more people take the vaccine, we should begin to see a decrease in hospitalizations and deaths first, because we are initially vaccinating those at highest risk. 

Next, we should see a decrease in the number of positive cases as the vaccine becomes available to everyone. At the point when our healthcare facilities are functioning at a relatively normal rate, the number of positive cases in the community is low, and a high percentage of people are vaccinated, then we will have some relief and return to some normalcy. This is certainly possible by late summer or early fall as long as people accept the vaccine and continue to practice public health prevention measures.

As the vaccine rollout eventually reaches a majority of the public, could this foster a premature or false sense of security and potentially another wave of the pandemic?

Cassidy: If the majority of the pubic are vaccinated — meaning over 80 percent — then we can begin to feel more secure. However, it’s not wise to assume that if everyone else gets the vaccine that you won’t need it. Anyone who is not vaccinated remains at risk of getting the virus, but the transmission should be slower. We also still have more to learn about how the vaccine affects transmission. 

Until we achieve herd immunity — meaning high levels of community protection, and very low rates of infection — we must continue to wear masks, watch our distance, wash hands and avoid crowds. Using all of these tools is still the fastest way back to some normalcy.

What do the new strains of COVID mean, and what precautions should people continue to take?

Cassidy: It’s normal for viruses to mutate. The new strains are believed to be much more contagious and [as of press time] it is unclear whether they are more deadly. However, if COVID-19 spreads much more easily, then more people can get ill and it can reach those at higher risk, which will increase hospitalizations and deaths. 

Scientists are confident that the vaccine will be effective against these new strains. The strains and future mutations will be monitored so that vaccine developers can respond and modify the vaccinations as needed.

We recommend a layered approach to prevention. It’s extremely important to be diligent about washing hands and wearing face coverings and keeping your distance from others and avoiding crowds and when it’s your turn, get vaccinated. 

For those who have had COVID and have recovered, are there risks with the new strains? 

Cassidy: There is some concern the South African strain can cause reinfections. When an individual recovers from COVID-19, they build up some natural immunity, but we do not know how long that protects someone from getting sick again. It can vary from person to person. Experts say vaccines likely provide stronger, longer lasting immunity as compared to infection.

For those who have had COVID, there can often appear to be a “survivor mentality” and lack of concern as they become more social and forego protective measures. What risks does this behavior represent, both for the recovered and for those who have not had COVID yet? 

Cassidy: Some people may be infected with enough of the virus to test positive on a COVID-19 test, but not enough to trigger a strong immune response. They may have mild symptoms or no symptoms at all even though they are infected with the virus. It is unclear whether they will create enough antibodies to protect against another infection in the future.

Initial results from a new study suggest that patients who have recovered from COVID-19 are likely to be protected against reinfection for several months. However, it’s possible that they may still carry the virus in their nose and throat and can transmit it to others.

COVID-19 has been circulating for a year now. While we have made extraordinary advances in knowledge, treatment and vaccines, we do not yet have long-term follow-up results on how long immunity lasts and the potential for reinfections. We must keep our guard up and protect ourselves and our families and friends so that we can reach a high level of herd immunity and community protection. We will get there together, and how soon depends on our individual actions. MKE