Based on various measures, the Johnson & Johnson COVID-19 vaccine has been shown to be less effective than those based on mRNA technology. It has also been linked to some rare blood clotting complications that recently prompted the CDC to revise its approval of the vaccine. Nevertheless, the vaccine is easy to manufacture, transport and store, and there have been some indications that it provides longer-lasting protection than some alternatives. And there have also been indications that at least some of the efficacy differences came from its use as a single-dose vaccine.
With all vaccines now expected to include a booster significantly after the initial vaccine dose, we are beginning to get a sense of how the J&J vaccine performs in more than one dose. Early results indicated that a J&J vaccine boosted by an mRNA dose produces a large increase in protective antibodies. But a J & J / J & J combination did not seem to be so effective.
Recent research advances may indicate, however, that protection continues to increase over time, engaging non-antibody-producing immune cells, and providing some protection against the omicron variant.
Change over time
One of the manuscripts traces a very large clinical trial that involved giving South African healthcare workers a second dose of the J&J vaccine six to nine months after their first dose. The timing of the trial meant that many of the participants were boosted shortly before the rise in omicron infections in that country.
The team tracked test results in the participants and adjusted the data for complicating factors such as age and known risk factors. Based on the need for hospitalization, the booster was obviously effective, and its effectiveness increased over time. In the two weeks after the boost, the effectiveness of preventing hospitalization was 63 percent. After the two-week duration, however, this rose to 84 percent and remained there for at least two months afterwards.
This increase in efficacy occurred even though omicron displaced delta as the primary source of new infections in South Africa. So this seems to be consistent with other results indicating that boosters help provide a much higher level of protection than initial vaccination doses alone.
This protection comes despite the fact that the antibody levels produced by the J&J vaccine are lower than those seen in mRNA vaccinations. As a result, South African researchers suggest that their findings are “indicative that protection against serious illness may be due to cellular immunity and immune memory rather than neutralizing antibodies.” Which brings us to the second pre-print, which looked at the cellular immunity that the T cells of the immune system provide.
To a T
This is a much smaller study involving only 20 participants from the Boston area. But it looks far more in detail at the immune response. It also looks at individuals who received either one or two doses, but due to the small study population, there are not enough people in both groups to make a separate analysis of these populations.
In any case, antibodies show a moderate but prolonged response and reach their peak about two months after vaccination. Their levels on day 240 were still about double the levels seen one month after vaccination. Neutralization against the delta variant was also quite robust, down by less than a third compared to the response to early strains.
But the striking results came when the researchers looked at the T cells that help recognize and kill infected cells. In these individuals, there was essentially no difference at any time examined. Other types of T cells declined somewhat, but also remained robust for eight months. Again, these are preliminary results from a small study, but it appears to be consistent with other reports of prolonged immunity produced by the J&J vaccine.
We are still a long way from fully understanding the interaction between vaccine-based immunity and the different variants that are now circulating, as well as the differences that may arise from the different methods of developing immunity. But many people, both in the United States and abroad, have now received the J&J vaccine, and understanding whether they face increased risks over time will be crucial to dealing with the pandemic in the future.