Americans who received the single-dose Johnson & Johnson Covid vaccine were better protected against serious illness and hospitalization during the Omicron wave if they received a second dose of Pfizer-BioNTech or Moderna vaccines, instead of an additional injection of Johnson & Johnson, according to a new study released Tuesday by the Centers for Disease Control and Prevention.
The report did not offer a comparison with the protection afforded by two doses of mRNA vaccines and included relatively few Johnson & Johnson recipients, making the results difficult to interpret.
The findings broadly support the added benefit of a booster dose versus the Omicron variant, which is known to partially bypass immune defenses. Yet the report is somewhat at odds with other data collected by the CDC which suggests that a single dose of the Johnson & Johnson vaccine prevented infections with the Omicron variant at least as, if not better, than two doses of mRNA vaccines.
These data indicate that people who received a single dose of the Johnson & Johnson vaccine are slightly more at risk of death than those who received two doses of mRNA.
Separately, South African researchers found that two doses of the Johnson & Johnson vaccine offer protection against serious illness and hospitalization comparable to that seen with two doses of the Pfizer-BioNTech vaccine.
The CDC now recommends that all adults who have received one or two doses of the Johnson & Johnson vaccine receive a booster dose of an mRNA vaccine. On Tuesday, the Food and Drug Administration cleared a second booster vaccine for all adults aged 50 and over, even those who have already received three doses of mRNA (i.e. two for full vaccination plus a booster).
In the new study, the researchers analyzed data from 80,287 Covid-related visits to emergency wards or urgent care clinics and 25,244 hospitalizations in 10 states. The data has been counted since December. 16, 2021 to March 7, 2022, when the Omicron variant was the predominant version of the virus.
A single dose of the Johnson & Johnson vaccine was 24% effective in preventing emergency room and emergency care visits, compared with 54% after two doses of the vaccine.
The study found that the effectiveness of a single dose of the Johnson & Johnson vaccine combined with a booster injection of an mRNA vaccine was similar to the protection of three doses of mRNA. (This finding is consistent with findings from other studies on booster shots.)
Vaccine efficacy against hospitalization showed a similar trend: 31% for a single dose of Johnson & Johnson, 67% for two doses of the vaccine, 78% for a dose of Johnson & Johnson vaccine plus one dose of an mRNA vaccine, and 90% after three doses of an mRNA vaccine.
But the margins of error for these estimates overlapped, meaning the differences might not be significant.
The researchers noted that the study had other limitations. The data does not include, on average, data beyond two months after receiving the last dose. Other studies have suggested that mRNA vaccines dropped dramatically in efficacy against infections after an initial spike, while the Johnson & Johnson vaccine performed better over the long term.
The study included less data on Johnson & Johnson recipients than those who received mRNA vaccines, making comparisons less reliable. For example, the researchers recorded 164 hospitalizations among people who received two doses of the Johnson & Johnson vaccine, compared with nearly 8,000 among recipients of three doses of mRNA.
And the overall numbers were too small to analyze vaccine recipients based on age, gender, or the presence of other health conditions, which may have skewed the results.