Who will get a third COVID-19 shot?

October 4, 2021


The Centers for Disease Control and Prevention recently expanded its recommendations on who should receive a booster COVID-19 vaccine to improve protection against the virus. People with certain autoimmune diseases were already able to get a third shot, and the new guidance includes people with underlying medical conditions and others who live or work in environments that are more likely to transmit COVID-19, such as health care professionals.

Richmond biology professor Angie Hilliker, an expert in RNA biology, recently weighed in on common questions around the third shot.

What is a ‘booster?’

The third shot is the same as the first two doses. Same dose, same type of shot. The third shot and the booster are the same thing, but the term booster usually refers to people who had the normal two doses of the vaccine, presumably had a normal immune response, but the immune response weakened over time. Getting another dose will trigger the immune system again and boost or increase the antibody production. People with suppressed immune systems have priority for a third shot, as two shots are often not enough to give them a normal immune response.

We need to get used to the idea that this virus will be around and that we will need updated vaccines to boost the immune system or protect it against future variants — like we do with the flu shot. And, like the flu shot, we also need to adjust our thinking from expecting nearly 100% protection against symptoms to high protection against severe symptoms, hospitalization, or death.

Who will need boosters?

As of now, the CDC and the FDA only recommend boosters for people over 65, the immunocompromised, and people with specific risk factors six months after their second dose. For the general population, the Department of Health and Human Services hopes that a third dose for all Americans will be approved. This is based on data that the vaccines are less effective at preventing infection with COVID eight months after vaccination. However, the vaccines are still highly effective at preventing hospitalization and deaths.

The story is nuanced, and there is controversy over it among scientists. Do we use doses of the vaccine to protect ourselves against any infection? Or do we share those doses with countries that have little access to vaccines?

Does the third shot need to be the same as the first two?

Currently, only the Pfizer COVID-19 vaccine is approved for boosters. Data on a possible booster for the Moderna COVID-19 vaccine and the Johnson & Johnson vaccine should be coming in the next few months. Because the Pfizer and Moderna vaccines are similar mRNA vaccines that target the same part of the virus, many people are wondering if they are interchangeable.

There are some studies that suggest mixing brands is safe, but public health officials are recommending continuity for now. The CDC recommends people wait to receive the same dose of the vaccine they have already gotten. However, for those in a high-risk group — if they got one of the two-dose mRNA vaccines but the same type is unavailable — the CDC says you can accept a dose from the other. But that sort of mixing and matching only pertains to the Moderna and Pfizer vaccines, which function similarly in the body. The Johnson and Johnson vaccine works in a different way.