The “One and Done” has arrived.
Health Canada has authorized the use of a fourth COVID-19 vaccine developed by Janssen (Johnson & Johnson’s pharmaceutical subsidiary) following ones by Pfizer, Moderna, and AstraZeneca. This new vaccine uses a harmless adenovirus vector to deliver the genetic information that instructs the body to produce the surface spike protein of the coronavirus (SARS-CoV-2), in order to trigger an immune response. The vaccine has been approved for use in people 18 years of age or older.
The J&J vaccine is a single dose vaccine, unlike the other three, which need two doses to reach maximum strength. The “one and done” factor means it will be ideal for vaccinating communities that are transient or at higher risk of not returning for a timely second dose, such as the homeless, or rotational workers. And it will be easier to administer for public health units, which won’t have to deal with the complicated logistics of giving second doses.
How does the Johnson & Johnson (J&J) vaccine work? How is the biological mechanism different from that of the mRNA vaccines?
Unlike the mRNA vaccines from Pfizer and Moderna, which deliver fat-covered bits of genetic material into your cells, the Johnson & Johnson vaccine uses a “shell of a virus” to carry genetic material into your cells. The “shell” is an adenovirus, which normally causes colds, but has been modified so that it can no longer replicate and make you sick.
The genetic material in the mRNA vaccines is RNA, whereas the genetic material in the J&J vaccine is DNA, but both encode the information to make the spike protein of SARS-CoV-2. Inside the adenovirus is the DNA that your body will use to make into RNA and then into the spike protein of the coronavirus.
In addition to being a single-dose vaccine, the J&J vaccine has standard refrigeration storage requirements, like the AstraZeneca vaccine. Adenovirus-based vaccines like the J&J COVID-19 vaccine and the AstraZeneca vaccine, are more resilient than mRNA vaccines from Pfizer and Moderna. DNA is not as fragile as RNA, and the adenovirus’s tough protein coat helps protect the genetic material inside. As a result, the Johnson & Johnson vaccine can be refrigerated for up to three months at 36–46°F (2–8°C).
Why is the Johnson & Johnson vaccine only one dose?
The J&J vaccine went into Phase III trials as a one-dose vaccine because earlier phase trials had shown strong immune responses after just one dose. After one dose, across all populations, even in older people. The antibody response and T-cell response were excellent and increased over time.
In trials, the J&J vaccine was found to be 66 percent effective overall in protecting against moderate to severe COVID-19, 28 days after injection. That exceeds the efficacy standards of Health Canada, the U.S. Food & Drug Administration, and the World Health Organization.
It was also 85 percent effective against severe COVID-19 alone. Of the roughly 45,000 people in the vaccine’s worldwide stage 3 trial—in which half got the shot, half got a placebo—464 people developed moderate–to–severe COVID-19 symptoms, Health Canada explained when announcing its approval. Of those 464 cases of COVID-19, 348 had received the placebo with 116 having received the vaccine.
What do we know about each vaccine’s ability to protect against the variants?
We know more about how the J&J vaccine protects against the coronavirus variants because the trials were conducted in South Africa and Brazil when the new variants had become prevalent. In South Africa, some 95 percent of the circulating virus was the B.1.351 variant and in Brazil, 69 percent of the circulating virus was a P1/P2 variant at the time of the trial. Although the J&J vaccine appeared to be less effective against mild and moderate disease in these regions, it remained strongly protective against severe disease, hospitalizations, and deaths. In the U.S., where the prevalence of variants was low, the overall efficacy of 72 percent likely was not affected by the variants.