Which mRNA Covid-19 Vaccine Works Better? Researchers Have Done A First Head-To-Head Comparison To Find Out

The researchers measured the effectiveness of the mRNA Covid-19 vaccines in terms of five Covid-19 related-outcomes: documented Covid-19, symptomatic disease, hospitalisation, ICU admission, and death

New Delhi: Researchers from the US Department of Veteran Affairs (VA), the Harvard TH Chan School of Public Health recently conducted the first head-to-head comparison of the effectiveness of the Pfizer-BioNTech and Moderna Covid-19 vaccines. They examined the electronic health records of veterans who had received these mRNA Covid-19 vaccines. The findings of the study were published on December 1, 2021, in the New England Journal of Medicine. 

Moderna Vaccine Observed To Offer An Increased Level Of Protection

The study said that both vaccines were highly effective in preventing Covid-19 outcomes such as documented infection, hospitalisation, and death. The researchers, however, stated in the study that the Moderna vaccine was observed to offer an increased level of protection. People who were vaccinated with the Moderna vaccine had a 21 per cent lower risk of documented infection, and a 41 per cent lower risk of hospitalisation, the peer-reviewed study said. 

Dr. J.P. Casas, one of the researchers of the study, said both vaccines are "incredibly effective", with only rare breakthrough cases, according to a statement by the Veterans Affairs Office of Research & Development. But regardless of the predominant strain, Moderna was observed to be "slightly more effective", he added. Earlier, the Alpha variant was the predominant variant, while the Delta variant is predominant at present. 

Vaccine Effectiveness Measured In Terms Of Five Covid-19-related Outcomes

The question of which of the two mRNA vaccines is more effective was previously unanswered, which the researchers addressed by designing a comparative effectiveness study. The researchers measured the effectiveness in terms of five Covid-19 related outcomes: documented Covid-19, symptomatic disease, hospitalisation, ICU admission, and death, the study said. In order to conduct the study, the scientists used data from the electronic health records of US veterans who received one of the two Covid-19 vaccines between early January 2021, and mid-may 2021. 

When the study was conducted, the Alpha variant was the predominant strain; hence, the study focused on this variant. As many as 2,19,482 recipients of the Pfizer vaccine were compared to the same number of recipients of the Moderna vaccine, according to the study. Based on a variety of clinical and demographic factors that could affect outcomes, the researchers matched the two groups, the study said.

Excess Cases of Documented Infection Per 1,000 people In Pfizer Vaccine Group

The study had a 24-week follow-up period, during which the researchers found the estimated risk of documented infection to be 4.52 events per 1,000 people in the Moderna vaccine group, and 5.75 events per 1,000 people in the Pfizer group, the study said. This means there was an excess of 1.23 cases of documented infection per 1,000 people in the Pfizer group, compared to the Moderna group. The Covid-19 related outcomes such as symptomatic Covid-19, hospitalisation, ICU admission, and death had an excess of 0.44, 0.55, 0.10, and 0.02 events per 1,000 people in the Pfizer group relative to the Moderna group, the researchers found. However, these differences were smaller, the authors noted in the study.

Moderna Vaccine Conferred A Lower Risk Of Covid-19 Infection

The researchers also conducted an additional phase of research, wherein they considered the Delta variant as the main strain. They observed that the Moderna vaccine conferred a lower risk of Covid-19 infection. In the Pfizer vaccine group, the excess risk of documented infection over 12 weeks was 6.54 events per 1,000 people, compared to the Moderna group, the study said. The researchers analysed a single Covid-19 outcome due to the shorter time frame available for the supplementary research. Since a smaller number of individuals were eligible for the analysis, the estimates were considered less precise, the study said.

Earlier, randomised trials had been conducted to compare the effectiveness of the mRNA vaccines against placebos, which had shown both vaccines to be very effective against symptomatic Covid-19 infection.

Dr. Barbra A. Dickerman, the lead author of the study, said either of the Moderna and Pfizer vaccines is recommended to individuals, according to the statement. She noted that estimated differences in effectiveness may be meaningful when considering the large population-scale at which the vaccines are deployed, despite the fact that they were small on an absolute scale. She added that the information may be helpful for larger decision-making bodies.

The researchers were able to identify even small differences in effectiveness of the two vaccines due to the large sample size covered by the expansive VA records system, the study said. The researchers used a methodology known as causal inference which could mirror randomised trials, which are the gold standard in health research. Causal inference is a type of data analysis that helps researchers draw firm conclusions about cause and effect.

Ensuring that the participants in the vaccine groups were comparable with respect to attributes that may predict the severity of infection or disease was a primary challenge, the authors noted in the study. Using the VA databases, the researchers precisely characterised recipients of each vaccine type and closely match them on the basis of age, sex, race, geographic location, and other attributes that may affect Covid-19-related outcomes, the study said. 

Further Evaluation Of The Vaccines' Comparative Effectiveness Needed

Dickerman said the fact that the two vaccine groups were extremely similar in terms of certain variables allowed the observational analysis to produce "exceptionally credible results" during a global emergency where answers are needed fast, according to the statement. The researchers are also conducting studies to find answers related to the comparative safety, versus effectiveness, of the Pfizer and Moderna vaccines. According to Dickerman, comparative safety is an "additional piece of the puzzle to support vaccine decision-making", the study said.

The authors noted in the study that further evaluation of the vaccines' comparative effectiveness and safety is needed. The authors concluded, "Given the high effectiveness and safety profile of both mRNA vaccines, either one is strongly recommended."