Just a couple of months ago, it was very difficult for most adults to get appointments for vaccination against SARS-CoV2 (the virus that causes COVID-19), and now, in many countries, including the United States, it is fairly easy. The reason why it is easy is not because nearly everyone is vaccinated, but rather because just about every adult who has been eager to be vaccinated now has received at least one dose of a COVID-19 vaccine. In the United States, most of those who still have not been vaccinated either fall somewhere along the spectrum of vaccine hesitancy — ranging from “I’m scared to get vaccinated for now, but will consider it after a few hundred million more people receive the vaccine and meanwhile I’m not so scared about getting COVID-19 or the prospect of getting infected and spreading the virus to other people” to “the vaccines are part of a conspiracy to inject people with microchips”— or are below the age of 16, or 18, depending on which COVID-19 vaccines are available in their locations. Currently, the emergency use authorization (EUA) from the FDA is in place for the Modern and Johnson and Johnson (Janssen) vaccines for those ages 18+ and for the Pfizer-BioNtech vaccine for ages 16+. However, at the time that I’m writing this, in early May, an EUA extension is expected that will make the Pfizer-BioNtech vaccine available down to the age of 12. This could happen within days, so it may begin by the time that this article is posted, or soon after. Soon after that, EUA extensions also are anticipated for Moderna and Janssen, also down to age 12, while the Novavax vaccine may receive an EUA covering adults very soon, with lower ages to follow. Meanwhile, clinical trials are in progress for COVID-19 vaccines in children ages 11 years down to 6 months.
As we have discussed previously, SARS-CoV2 infection in children can lead to severe disease, but much more rarely compared with adults, so many people wonder why the children should be vaccinated, or why pediatric vaccination should be required. Well, the answer has to do with the fact that children spread the virus plus the fact the vaccine hesitancy among adults. To get the pandemic under control, we need to get a lot of people vaccinated. It comes down to a numbers game related to the capability of the virus to spread, and so to compensate for the numerous anti-vaxxer adults and the adults who are hesitating because they believe, mistakenly, that the vaccines are risky and want other people to take the risks in their stead, millions of children, beginning with the young teens, are standing by ready to step up to the plate. Vaccination is a community thing. They are a component of public health, emphasis on the word public. Like agreeing to turn off the lights and use blackout curtains in your home during an air raid in London in World War II, the argument about contributing to the protection of the community must be balanced against the argument about your personal freedoms.
As for the numbers game, if you have been reading what we have been posting here on The Pulse about a variable used in epidemiology called the R0 (pronounced R naught), it will seem very straightforward. R0 represents the average number of people that an already-infected individual infects. If R0 equals 1, then each infected person infects just one other person, which means that that the number of cases does not increase over time. If R0 equals 2, then each infected person infects two other people, so the number of infected people doubles over the average amount of time that the infection takes to spread from person to person, and the number of cases doubles over an amount of time that depends both on how long it takes for the infection to spread from person to person and how long it takes for people to become symptomatic.
In the case of SARS-CoV2, the R0 is now thought to be in the range of 2.5 to 4, with the more infectious variants being closer to 4 than 2.5. Maybe, some variants are emerging with an R0 higher than 4, for instance approaching 5, but let’s use an R0 of 4.0 here. In order to get control over the pandemic, we need herd immunity, which means having a certain minimum fraction of people immune, either through vaccination or previous infection with the virus to prevent the virus from increasing its prevalence in the community. That needed fraction depends on the R0 and there is an equation for calculating it. You take the reciprocal of the R0, meaning 1 divided by the R0, and then you subtract that number from 1. Thus, for a variant of SARS-CoV2 whose R0 equals 4.0, we divide 1 by 4, which gives us 0.25, then we subtract 0.25 from 1, which gives us 0.75, or 75 percent, meaning that for herd immunity we need a minimum of 75 percent of all people who are in interacting community to be immunized, either through vaccination or having been infected with the virus. Now, certainly there are places with higher fractions of the population being vaccine hesitant or anti-vaxx and other places where people are more compliant about getting their vaccines, but overall, we are talking about 75 percent, and experts think we should consider 80 percent as the target, because of new variants that may have an R0 closer to 5.0 (1/5 = 0.2; 1-0.2 = 0.8). Except in places where nearly all of the adults get vaccinated, we cannot get to 75 percent or 80 percent of people, if the children are not vaccinated too. And so there is a direct connection between the vaccine hesitancy among adults and the need for COVID-19 vaccination to be expanded to children.