Vaccine protective power refers to the reduction in the risk of disease, serious illness or death in vaccinated people compared to unvaccinated people. A protection level of 0% means that the vaccine is completely ineffective and the risks mentioned above are the same as in the control group; conversely, 100% means that the vaccine is 100% effective and the risks are completely eliminated. The assessment of protection can be divided into two phases. In the Phase III clinical trial, the incidence of disease in thousands to tens of thousands of vaccinated subjects will be compared with that in non-vaccinated or placebo subjects, known as Vaccine Efficacy. Once the vaccine is available, the effectiveness of the vaccine will continue to be tracked after widespread administration on a large scale, known as Vaccine Effectiveness.

Results of the Phase III clinical trial analysis [1] of both the mRNA-1273 vaccine developed by Moderna, and Pfizer's BNT162b2 vaccine were published in the New England Journal of Medicine in late December 2020. The results showed that protection against symptomatic COVID-19 infection was 94.1% at 14 days after receiving a second dose of mRNA-1273 vaccine and 95% at 7 days after receiving a second dose of BNT162b2 vaccine.

The two mRNA vaccines have been licensed for emergency use and have been administered on a large scale in many countries around the world. Subsequent studies on the "real-world" protection of the Pfizer BNT162b2 vaccine have been conducted in a number of countries. In Israel [2], a total of nearly 1.2 million people were analysed and showed 92% protection against all infections, 94% protection against symptomatic infections, 87% protection against hospitalisation and 92% protection against severe illness 7 days after the second dose of the vaccine. In the UK, a study of 7.5 million elderly people aged 70 years or older [3] demonstrated 85% protection 14 days after the second dose of the vaccine. The US CDC also analysed the protective effect of vaccination in 3,950 high-risk working populations and showed [4] that protection against infection could reach 80% after two weeks of a single dose of Pfizer or Moderna vaccine, regardless of whether the infection was symptomatic, and could be increased to 90% after completing two doses.

An article published on 4 January this year on BMJ Opinion, a self-published online forum run by the British Medical Journal (BMJ) (which is not a formal scientific publication and on which any registered user can post comments), was titled, "Pfizer and Moderna vaccines are 95% effective - we need details and raw data," authored by Peter Doshi, Associate Professor at the University of Maryland School of Pharmacy. The article strongly questions the results of the protective power analysis obtained in the Phase III clinical trial of Pfizer's BNT162b2 vaccine. The authors concluded that the Pfizer data reported that 8 people in the vaccination arm and 162 in the placebo arm were infected with the novel coronavirus, 170 of whom were confirmed to be infected by PCR nucleic acid testing. A further 3410 people in the data showed clinical symptoms or imaging similar to COVID-19 discomfort, but had negative PCR results; 1594 in the vaccination group and 1816 in the placebo group. These individuals were classified as "suspected COVID-19 cases." The authors concluded that the possibility of COVID-19 in these individuals could not be ruled out. Therefore, if all 3410 people were included in the number of infections that occurred, the BNT162b2 vaccine would provide only 19% protection. If this figure is extended to exclude 'suspected cases' within 7 days of vaccination (as the antibodies had not yet been produced), then the vaccine protection would be 29.5%.

It can be seen that the above protection figure was obtained from the authors' logic that "although 3410 people had negative PCR results, they should all be counted as NICs because they had symptoms of discomfort." However, this is very unreasonable.

First of all, PCR is extremely sensitive in detecting nucleic acids, so it is possible to detect carriers of the virus at an early stage of infection. Therefore, it is common to see an asymptomatic infection with a positive PCR; it is very rare to see a patient with COVID-19 infection who is already symptomatic but has a negative PCR. If all 3410 suspected patients were treated as infected according to the authors, the PCR pseudo-negative rate in this clinical trial would be 95.2%, which is clearly unreasonable.

Secondly, Pfizer's BNT162b2 vaccine has undergone rigorous review and has received emergency authorisation for use in the US, UK and EU. In particular, the US FDA released a Briefing Document [5] to the public regarding the BNT162b2 vaccine data review committee, which documented how the reviewers thought about the data in question. The "suspected cases" mentioned by the authors are also documented in the Briefing Document. It is unlikely that national reviewers would agree to allow a vaccine to be licensed for emergency use if it had only 19%-29.5% protection, well below the 50% threshold required for emergency authorisation.

The article in the BMJ Opinion was published in early January this year, and the BNT162b2 vaccine has been undergoing large-scale post-vaccination efficacy studies in a number of countries to date, in addition to the clinical trial results published in December last year, to demonstrate the efficacy of the vaccine after vaccination. Of course, these two mRNA vaccines are new technologies and products unprecedented in the history of human vaccines, and as the authors point out, experts really need more detailed raw data before they can participate and examine the credibility of the data on a case-by-case basis to improve public confidence in the vaccines.

1. Baden et. al.. (2020) Efficacy and Safety of the mRNA-1273 SARS-CoV-2 Vaccine. N Engl J Med. 384:403-416；Polack et. al.. (2020) Safety and Efficacy of the BNT162b2 mRNA Covid-19 Vaccine. N Engl J Med. 383:2603-2615.
   ‍
2. Dagan et. al.. (2021) BNT162b2 mRNA Covid-19 Vaccine in a Nationwide Mass Vaccination Setting. N Engl J Med. 384:1412-1423. DOI: 10.1056/NEJMoa2101765
   ‍
3. ‍New data show vaccines reduce severe COVID-19 in older adults. (2021)
   ‍
4. ‍Interim Estimates of Vaccine Effectiveness of BNT162b2 and mRNA-1273 COVID-19 Vaccines in Preventing SARS-CoV-2 Infection Among Health Care Personnel, First Responders, and Other Essential and Frontline Workers — Eight U.S. Locations, December 2020–March 2021 (Morbidity and Mortality Weekly Report (MMWR)
   ‍
5. ‍FDA Briefing Document, Pfizer-BioNTech COVID-19 Vaccine - Vaccines and Related Biological Products Advisory Committee Meeting December 10, 2020

‍