• Dr. Soumi Eachempati

What do all these vaccine trials mean?

Updated: Aug 12, 2021

This past week vaccine trial information packed the news cycle with blinding rapidity. No less than 4 major companies released important data on early studies for Covid-19 vaccine results. Company spokespeople and television commentators gushed about the merits (and less so the shortcomings) of each of these trials. Pundits everywhere claimed auspicious victory and the beginning of the end in the fight against the scourge of Covid-19.

Unfortunately, data trajectories and requirements are more complicated than that.

Vaccines have many characteristics that mandate attention. They need to be safe and function well in all age groups. That is a tall ask by itself. However, some would argue they need to be most effective in older populations and individuals with co-morbidities where the population has a higher chance of death with affliction of Covid-19. Consequently, most vaccine trials take 6-10 years. Some diseases, like SARS, a viral cousin of Covid-19, never receive a successful vaccine.

Successful vaccine production has an extremely high bar. For a vaccine to be a success, it has to stimulate immune cells that fight against Covid-19, preferably with a single dose. In Covid, scientists make a distinction between antibodies that simply bind to the spike protein portion of the virus and those that can plausibly prevent infection during examination. The latter called “neutralizing antibodies and are regarded as tantamount for an approvable vaccine. The best vaccines would also stimulate T-cell responses which would recognize and kill Covid-19 cells. The last qualification of a strong vaccine product would be that it could be scaled in manufacturing to produce billions of doses in a calendar year.(Like 2021.)

The four entities that reported data for the vaccine studies within the past 7 days included CanSino from Wuhan, Moderna, Pfizer/BioNTec, and the AstraZeneca/Oxford group. Each of them had their own stories and reason for optimism but since each reported early phase data, there was inarguably room for data improvement, larger series, and longer follow-up. Perhaps most notably, none of them actually showed (or will ever show prior to approval) that their product actually prevents death or illness from Covid-19.

The Moderna trial created an enormous amount of attention from news media and investors when it was released last week. The trial was published in the New England Journal of Medicine concurrent with its data release and investor call. This vaccine was studied in patients 18-55 years of age and required 2 doses 4 weeks apart for its effect. The vaccine did produce a neutralizing antibody response that exceeded the antibody level of individuals who had already been infected with Covid-19 and the data was called “promising” in the accompanying NEJM editorial. Also praised in the editorial was the process in which the trial compressed essentially 6 years of research into 6 months. The Phase 2 study for this product is starting imminently with older patients and Phase 3 is already scheduled. Concurrently, manufacturing is already starting. Things are moving faster for Covid-19 than any other disease in history.

The AstraZeneca/Oxford group also uses an adenovirus vector like the CanSino product. However, the AZN/Oxford agent uses a genetically modified chimp adenovirus so humans do not have a preexisting antibody response to this vector. The trial released in the British journal Lancet on 7-22-20 revealed that the vaccine did produce neutralizing antibodies in humans and also immune T-cells. While the results were generally positive, enthusiasm was dampened by the realization that the company was going to employ the two-dose strategy as well.

CanSino had reported Phase 1 data for their vaccine in May but this week reported its Phase 2 trial with a publication in the British journal Lancet. This group reported some success and will be used by the Chinese military as it enters Phase 3 trials. This product used a live attenuated adenovirus that delivered a genetic version of the Coronavirus spike protein to the host. In some patients, this stimulated the production of neutralizing antibodies and even a T-cell response. Unfortunately, many patients (almost half) had preexisting antibodies to the adenovirus vector and in these patients the antibody response was not nearly as strong especially in the older patients.

Pfizer and BioNTech performed concurrent trials in the US and Germany on their vaccine product. The US trial released data early in the month but the German trial results were released just this Monday along with the flurry of AstraZeneca and CanSino data during the workday. The Pfizer/BioNTech data here were again generally favorable and may have represented the best trial results of the companies mentioned. The product created neutralizing antibodies and also importantly functional T-cell responses.

The work of all these companies and their scientists is nothing short of incredible. Nonetheless, the challenges going forward need to be appreciated. Most of the products require two doses and have been only tested in healthy younger volunteers. While researchers are measuring neutralizing antibody and T-cell levels, they have no standard to understand what level is sufficient to be protective against Covid-19 infection or symptoms. The elderly and vulnerable populations with the highest risk of death to Covid-19 infection have not been even tested for safety. The studies also do not evaluate whether the vaccine can prevent individuals from being potentially contagious to unvaccinated individuals, as the virus may not be fully killed in an individual after infection. This consideration is important when the need to vaccinate all the necessary individuals occurs over many months.