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Johnson and Johnson Vaccine

 New vaccine candidate linked to long lasting antibody levels

    COVID-19 vaccines have recently become the hot topic of many conversations. Two vaccines in particular, have been all over the media; one developed by the company Moderna and the other by Pfizer. Both vaccines are mRNA based and according to the Centers for Disease Control and Prevention, are the only vaccines "authorized and recommended to prevent COVID-19," (as of Jan. 15, 2021). However, many COVID-19 vaccine candidates are currently under development and undergoing clinical trials. One candidate in particular, although in its early stages of testing, displayed hopeful results; the vaccine was associated with long lasting antibody levels in all ages. Unlike the Pfizer and Moderna vaccines, this candidate is not mRNA-based but rather an adenovirus-based vaccine. The results for the phase 1-2a trial of this vaccine were published in the New England Journal of Medicine on January 13, 2021.

What is an Adenovirus Vaccine

    The vaccine discussed in this article is a replication-incompetent adenovirus serotype 26 vector vaccine (Ad26.COV2.S.) This type of vaccine uses a weakened form of an adenovirus, which encodes a SARS-CoV-2 spike protein. This spike protein then generates an immune response specific against the coronavirus. Unlike mRNA vaccines which are relatively new, adenovirus-based vaccines have been around for some time and have been used to fight off other viruses including human immunodeficiency virus (HIV).

About the Trial

    The trial, funded by Johnson & Johnson, was first initiated on July 22, 2020, throughout Belgium and the United States. Over 800 healthy adults were enrolled and split into 3 cohorts by age, but only the results from cohorts 1 and 3 were reported in the publication. Cohort 1 consisted of 402 participants between the ages 18-55 and cohort 3 consisted of 403 participants aged 65 years or older. Participants in each cohort were randomly split up to either receive a high-dose of the vaccine, a low-dose, or placebo.

Is it Safe: Adverse Events

    Overall, the vaccine can be considered safe as it only produced a few mild symptoms that got better with time. Low grade adverse events such as fatigue, headache and muscle pain were the most frequent adverse events observed in both cohorts after vaccination. In cohort 1, these adverse events were reported in 65% of low-dose recipients , 84% of high-dose recipients, and 26% of placebo recipients. Cohort 3 had low grade adverse events reported in 46% of low-dose recipients, 55% of high-dose recipients, and 23% of placebo recipients. While a few other adverse events were reported, fatigue, headache, muscle pain, injection-site pain and fever were the most common. Adverse events were less common in cohort 3 than cohort 1 and in recipients of a low-dose rather than a high-dose. Adverse events also decreased after a second vaccine dose.

Is it Effective: Antibody and T-Cell Response

    To understand the efficacy of a vaccine, it's important to understand how a vaccine works. Vaccines trigger the activation of two critical mechanisms: antibodies and T-cells. Antibodies prevent and reduce infections by binding to and destroying antigens like the coronavirus.  Meanwhile, T-cells reduce, control, and destroy infected cells. The presence of high levels of antibodies and T-cells are good indicators that a vaccine is efficacious and generating an immune response.

    By day 29 after the first vaccine dose, potent COVID-19 antibodies were detected in over 90% of all participants regardless of age or vaccine dose. By day 57, even higher antibody levels were detected in 100% of participants in Cohort 1. A second vaccine dosage, administered to cohort 1 on day 57, caused over a 2 fold increase in antibody levels. Antibody levels continued to remain stable until at least 71 days after the first vaccine dose in all participants of Cohort 1. The company plans to release further data regarding Cohort 3 later this month. 

    T cells are another component of the immune system whose presence can help determine the efficacy of the vaccine. The major roles of the T cell are to kill infected cells and activate other immune cells. One type of T cell measured in this trial was the CD4+Th1 cell. By day 15, Th1 was detected in 76% of low-dose recipients and 83% of high-dose recipients for cohort 1 and in 60% of low-dose recipients and 67% of high dose recipients in cohort 3. According to the published study, the results "indicated a vaccine induced Th1-skewed response", meaning that the vaccine was the cause of the detectable T-cell levels.
    

Summary

    The findings of the phase 1-2a trial report that the Johnson and Johnson vaccine produced high levels of antibody and T-cells while being associated with mild symptoms. This durable immune response is a promising outcome of the study and results indicate that the vaccine is safe and effective in both younger and older adults. The positive results from this trial supported the researchers decisions to proceed to larger phase 3 trials. However, keep in mind that the clinical trial conducted was a phase 1-2a trial and results for the vaccine efficacy in larger phase 3 trials are pending. (See Vaccine for COVID: What you need to know for more). While the findings from this trial are encouraging, it is important to wait on data from the phase 3 trial before making any conclusions. 

Sources

1. Sadoff, Jerald, et al. “Interim Results of a Phase 1–2a Trial of Ad26.COV2.S Covid-19 Vaccine: NEJM.” New England Journal of Medicine, 31 Dec. 2020, www.nejm.org/doi/10.1056/NEJMoa2034201. 

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