KAMIL KRZACZYNSKI / Contributor/Getty Images
  • A booster dose of J&J vaccine gave comparable protection to other vaccines, the company said.
  • The second shot was found to give 100% against severe disease, it said, citing a study.
  • The second shot was also 94% protective against symptomatic infection.
  • For more stories go to www.BusinessInsider.co.za.

Two doses of the Jonhson & Johnson Covid-19 vaccine provided an efficacy similar to that of the Moderna and Pfizer vaccines, the company said on Tuesday.

The company said in a press release, citing its own studies, that the booster provided:

  • 94% protection against symptomatic infection,
  • 100% protection against severe disease at least 14 days after the second shot.

The second dose was administered two months after the first dose, the company said.

The figures are based on a 30,000-patient study, called ENSEMBLE 2, in which a second dose was given to volunteers 56 days apart, STAT News reported.

Of those, 14 cases of moderate-to-severe Covid had received two doses, compared to 52 among those given placebo doses. Zero were severely or critically ill, the company said in a press release. 

The data has not been peer-reviewed or published in a peer-reviewed journal, The Wall Street Journal noted.

The shot was first presented as a single-dose vaccine, unlike the two-shot regimes for Pfizer and Moderna.

But a clinical study revealed that a single J&J dose was less effective than the other approved vaccines. 

The study put the vaccine's efficacy at 66% at preventing symptomatic disease. By comparison, clinical trials put the the two-dose Moderna and Pfizer efficacy against symptomatic disease at risk 94 and 95%, respectively, although it is difficult to compare trials with different protocols head to head. 

A recent CDC study confirmed the gap in efficacy between the shots. The study found that  the single-shot J&J vaccine still greatly reduced the risk of hospitalization from Covid-19 — by 71%.

But the two-dose Moderna and Pfizer further reduced the risk, by 93% and 88%, respectively.

US officials have approved only the single-dose approach for the J&J vaccine, and would need to take further steps to authorise second doses.

Get the best of our site emailed to you every weekday.

Go to the Business Insider front page for more stories.