Does Everyone Need a Yearly Covid Booster?

The most recent recommendation by the CDC has come under question.

On September 12, 2023, the CDC recommended a booster dose of Covid vaccine for everyone over 6 months of age. To understand why, we need to go back to the beginning.

In December 2020, two Covid mRNA vaccines became available. Given as a series of two doses, both were shown to be more than 90 percent effective at preventing severe disease in placebo-controlled studies. One year later, the CDC found that two doses of these vaccines remained highly effective at preventing severe disease. The goal of Covid vaccines is to keep people out of the hospital, out of the intensive care unit, and out of the morgue. By the end of 2021, the mRNA vaccines were doing exactly that.

Then, the omicron variant entered the United States. Omicron was different. Unlike the variants that had been circulating in 2021 (i.e., alpha and delta), omicron was immune evasive. Many people who had been previously vaccinated were getting mild infections, some severe disease. In response, the CDC performed a series of studies at the beginning of 2022 to determine whether booster doses of mRNA vaccines protected against severe disease caused by omicron. They found that a third dose and, to a lesser extent, a fourth dose decreased hospitalizations. But not everyone benefited. Those most likely to benefit were elderly, immune suppressed, pregnant, or had multiple health problems such as diabetes or chronic lung, liver, kidney, or heart disease.

The CDC is now arguing that, given the continued evolution of SARS-CoV-2, we should offer a yearly Covid vaccine in a manner analogous to the influenza vaccine. SARS-CoV-2, however, isn’t influenza. Every year, FDA advisors pick strains to include in the yearly influenza vaccine. If they’re wrong, which has happened three times in the past twenty years, protective efficacy against severe disease can fall below 20 percent. In other words, pick the wrong influenza strain and you’re in trouble. That’s not true for SARS-CoV-2. Healthy young people who have been vaccinated against SARS-CoV-2 with the original vaccine remain protected against severe disease because the parts of these new variants that are recognized by T cells have remained relatively unchanged. T cells, which are long-lived and kill virus-infected cells, are critical in protecting against severe COVID. By likening SARS-CoV-2 to influenza, we have created the false perception that healthy young people who have already been vaccinated or naturally infected or both will be protected against severe disease only if they receive the updated vaccine.

The United States is now an outlier. Health officials in the United Kingdom, Sweden, Germany, Norway, Finland, and the World Health Organization (WHO) recommend booster dosing only for those at highest risk. Regarding vaccinating healthy young people, the WHO stated, “Although additional boosters are safe for this group, [we do] not routinely recommend them, given the comparatively low public health returns.”

Most people in the United States have now been both vaccinated and naturally infected. This “hybrid immunity” likely induces broad, long-lived protection against severe disease. At this point in the pandemic, it is hard to make a case for vaccinating everyone. Let’s focus on those who are most likely to benefit. Otherwise, we run the risk of further confusing and frustrating the American public.