There were a couple of big changes in the COVID vaccine landscape last week. On Thursday, February 25, the FDA reissued its EUAs for the Pfizer and Moderna COVID-19 vaccines, revising portions of their original EUAs. On Saturday, February 27, the FDA issued a new EUA for the Janssen COVID-19 vaccine, commonly known as the Johnson and Johnson vaccine. Lots of news, too much for one blog. Let’s address the important information one bite at a time, starting with the Janssen vaccine.
Like all other COVID-19 vaccines, the Janssen vaccine has not been approved for use by the FDA. Instead, these vaccines are authorized for use in the U.S. This authorization is based on the FDA’s authority to make unapproved products available during an emergency when “there are no adequate, approved, and available alternatives.” As stated in the EUA letter issued February 27, 2021, “It is an investigational vaccine not licensed for any indication.” This means that clinical trails on vaccine safety and effectiveness have not been completed. Expect comprehensive analysis of clinical trials this summer at the earliest.
However, the Janssen vaccine differs from the other two vaccines in important ways. First, it is not an mRNA vaccine. Rather, it is a recombinant vector vaccine. This vaccine is made by inserting genetic code for a protein of the target into a harmless virus (the “vector”). When injected, this harmless virus presents the target proteins to the immune system, causing formation of antibodies, in this case antibodies to the spike proteins on the SARS-CoV-2 capsule. This technology is not entirely new. Manufactured (or “recombinant”) genetic code has been used to synthesize proteins for vaccines for nearly a decade. Recombinant flu vaccines received FDA approval in 2013. You may have received a recombinant flu vaccine in recent years. The difference between recombinant protein vaccine and viral vector vaccines has to do with where the antigenic proteins are made–either in your body (viral vector) or outside your body (recombinant protein). The harmless virus (the “viral vector”) cannot replicate within your body, so the effect is the same.
There are more differences. According to data submitted to the FDA, the Janssen vaccine is less effective preventing moderate to severe COVID-19 than the Moderna and Pfizer vaccines. The Janssen vaccine requires only one doses compared to the two doses required by Moderna and Pfizer. Storage of the Janssen vaccine is easier to accomplish than the other two. Vaccines features are compared as follows:
| Pfizer | Moderna | Janssen | |
| Vaccine Technology | mRNA | mRNA | Recombinant Vector |
| FDA Approval | No | No | No |
| Effective rate | 95% | 95% | 66% |
| Minimum Age | 16 years | 18 years | 18 years |
| Doses | 2 | 2 | 1 |
| Storage | -70°C | -70°C | Refrigerated |
| Time between doses | 3 weeks | 1 month | Not applicable |
There is another difference. In its reissued EUA, the FDA has required Pfizer to disclose post-authorization adverse events in its fact sheet to health care providers. We will discuss that next time.
