HJNO Mar/Apr 2021

HEALTHCARE JOURNAL OF NEW ORLEANS I  MAR / APR 2021 11 be higher. Some adults will have acquired some natural immunity by acquiring the infection directly. Modeling indicates that immunity required to achieve natural herd immunity might be only 40% if those who are most likely to spread the virus are also immune to the virus. It’s possible a combi- nation of natural immunity in those most likely to spread the disease, voluntary vac- cine uptake in the general population, and immunization of children may get us close. But, we don’t have a vaccine authorized for use in children under 16 yet. Krousel-Wood: In order to put a “lid” on COVID-19, we must achieve immunity in about 80% of the population to achieve herd immunity or community immunity. Vaccines teach our immune systems to create proteins that fight disease, known as 'antibodies', similar to what would happen when we are exposed to a disease but, importantly, vaccines work without making us sick from the disease. Herd immunity happens when a large portion of a community (the herd) becomes immune to a disease — either through infection or through vaccination — making the spread of disease from person to person unlikely. As a result, the whole community becomes protected, not just those who are immune. There are two ways to herd immunity for COVID-19 — vaccines and infection. Smallpox and polio are two examples of vaccines successfully controlling deadly, contagiousdiseasesthroughherdimmunity. Of note, if there is a large portion of the population that is hesitant to vaccinate and does not get vaccinated, this presents a real challenge to achieving community protection through herd immunity. Editor We live in a global community, but it seems a rather daunting task to achieve herd immunity from COVID-19 worldwide. If the U.S. achieves it and other countries do not, is that really herd immunity? Stoecker: Again, herd immunity is a patch- work quilt and for a time, life could be quite different in some locations. Compare the images of large street parties in New Zea- land to the prospect of a canceled Mardi Gras in New Orleans. GAVI’s COVAX initia- tive is a mechanism to redistribute vaccina- tion resources from wealthy countries to developing countries. President Biden has committed the U.S. to this initiative to ad- dress global inequities in coronavirus vac- cine access. Krousel-Wood: If the proportion of vacci- nated people in a community falls below the herd immunity threshold, exposure to COVID-19 disease could result in the disease spreading rapidly. We have seen this happen with the recent resurgence of measles in several parts of the world with relatively low vaccination rates, including some areas in the United States. By achiev- ing high immunity rates (about 80%) in our communities through vaccination, we will protect our communities from spreading COVID-19. Editor If all goes as planned, what timeta- bles are you seeing for herd immunity in our communities? Stoecker: With promising results from a third vaccine freshly announced, I’m op- timistic that I might go inside a restaurant sometime this summer! Krousel-Wood: This depends on the roll- out of vaccines and the proportion of the population in the community getting vac- cinated. In December 2020, NAIAD direc- tor, Anthony Fauci, MD, outlined a plan that would have 75-80% of Americans vac- cinated by the end of summer 2021 and a return to some sense of “normalcy” by the end of 2021. However, the success of this timeline depends on high vaccination rates that achieve herd immunity in our commu- nities. The impact of the COVID-19 variants on herd immunity is yet to be determined. Importantly, getting a vaccine does not mean instant success. Until at least 80% of the population achieves immunity through infection or vaccination, we must contin- ue to use prevention measures, including wearing masks, physical distancing, hand hygiene and disinfecting high-touch areas to reduce the spread of COVID-19. n “Herd immunity is a patchwork quilt as we have seen with outbreaks of measles in some schools but not others.” — CHARLES STOECKER, PHD