The air is brisk, the days are shorter, and the temperature is dropping, which can only mean one thing: It’s respiratory virus season. Or at least it’s a notable season for us health care workers, especially those of us who work in pediatrics. Respiratory viruses increase in prevalence during the winter months. This is because viruses can survive longer in colder temperatures and lower humidity and because people spend more time inside during the winter. But I’m not here to remind you of elementary science. I’m here to talk about the science behind the Covid vaccine and some of the uncertainties.
How effective are Covid vaccines? Data demonstrates the efficacy of the SARS-CoV2 (Covid) vaccines through the decreased number of positive tests and hospitalizations related to Covid. The most recent and frequent types of studies are observational in nature, because the environment and variables do not have to be controlled as in randomized controlled trials. They add value and attestation to the original clinical trials that Pfizer, Moderna, and Johnson & Johnson (J&J) conducted in order to get FDA emergency authorization. An observational study published in October by The New England Journal of Medicine demonstrated that the effectiveness of full mRNA vaccination (Pfizer or Moderna) was 89% against laboratory-confirmed SARS-CoV-2 infection leading to hospitalization, 90% against infection leading to an ICU admission, and 91% against infection leading to an emergency department or urgent care visit. The effectiveness of the J&J vaccine was 68% against laboratory-confirmed SARS-CoV-2 infection leading to hospitalization and 73% against infection leading to an emergency department or urgent care visit.
But what about booster shots? The data from observational studies suggests that breakthrough Covid infections are becoming more prevalent six months to a year after initial vaccination. Booster shots are required with many other vaccines, particularly vaccines containing inactivated virus strains (like J&J). For example, the Centers for Disease Control and Prevention (CDC) recommends that all adults get a Tdap booster every 10 years, which is a mixed vaccine immunizing us from tetanus, diphtheria, and pertussis. As new strains begin to circulate, it makes sense that we would need booster shots for Covid too. We require flu shots annually for that very reason. There are multiple strains of the flu virus and scientists attempt to predict each year which strains will be most prevalent when making the flu vaccine. That is why flu vaccines tend to only be 40-60% effective. The data on the necessity of a Covid booster vaccine is limited but is there in two observational studies performed in Israel this summer. In mid-June, the Delta variant became dominant in Israel and the government authorized a third dose for immunocompromised residents and residents ≥60 by the end of July. The authorization was then expanded to ≥12 years at the end of August. Preliminary results have demonstrated that the rates of confirmed Covid and severe illness related to Covid were substantially lower among those who received a booster shot. The rate of confirmed infection was lower in the booster group than in the non-booster group by a factor of 11.3 (95% confidence interval) and the rate of severe illness was lower by a factor of 19.5. This table does a better job of explaining the importance of the data than I could.
Should I mix and match? The FDA and CDC recently supported a “mix-and-match” approach that allows people to choose a different vaccine for their booster than the one they started with. One of the great things about mRNA technology, which the Pfizer and Moderna vaccines use, is that it’s easy to change the mRNA to match variants, and they can be quickly produced at scale. “This is different from the manufacturing process for the most commonly used flu vaccines, which is a much slower process because influenza virus strains need to be grown in chicken eggs, from which a particular viral protein is purified and formulated into a vaccine,” says Dr. Albert Shaw, an infectious disease specialist at Yale Medicine. Meanwhile, the J&J vaccine uses a specific dead virus called adenovirus 26. The difference between the J&J and mRNA vaccines is that the J&J “is engineered to be unable to reproduce itself to introduce a version of the SARS-CoV-2 spike protein—the target of the mRNA vaccines—into cells to generate a protective immune response,” according to Dr. Shaw. Being able to mix and match increases flexibility. You can choose the booster depending on the vaccine that is available and potential vaccine reactions you may have experienced in the past. There are no additional safety concerns with mixing and matching. Therefore, there are no bad choices. Regardless of what booster you get, you will still develop an immune response with an increase in antibodies against SARS-CoV2.
What are the CDC’s current recommendations about who can get booster shots? As of November 11, 2021, you are eligible to receive a Pfizer or Moderna booster if you are 65 years of age or older (as many of you are at Stern…kidding), are 18+ and live in long-term care facilities, have underlying medical conditions, or work in high-risk settings. Boosters for people who meet this criteria are recommended at six months after their second shot. For those who received a J&J vaccine, everyone 18+ is eligible to receive a booster two months after their initial shot. And yes, you can try Moderna or Pfizer this time.