Covid-19 Vaccine Resource Center (NEJM 2021.4.2)①

Frequently Asked Questions

・How do the Pfizer and Moderna Covid-19 vaccines work?

Two messenger RNA (mRNA) vaccines are currently available in the United States, one developed by Pfizer/BioNTech (BNT162b2) and the other by Moderna (mRNA-1273). In these vaccines, the mRNA carries instructions to make the SARS-CoV-2 "spike" protein -- the prickly projections on the surface of the virus, which is structured like those rubber balls that dogs love to chase or like the quills of a porcupine.

Once the vaccine is injected, the mRNA is taken up by the macrophages near the injection site and instructs those cells to make the spike protein. The spike protein then appears on the surface of the macrophages, inducing an immune response that mimics the way we fight off infections and protects us from natural infection with SARS-CoV-2. Enzymes in the body then degrade and dispose of the mRNA. No live virus is involved, and no genetic material enters the nucleus of the cells.

Although these are the first mRNA vaccines to be broadly tested and used in clinical practice, scientists have been working on mRNA vaccines for years. And despite this wonderful parody piece. opens in new tab saying that the technology is "obvious," in fact the breakthrough insight that put the mRNA inside a lipid coating to prevent it from degrading is quite brilliant -- and yes, this may be the first time the New England Journal of Medicine has referenced a piece in The Onion. (Last reviewed/updated on 14 Mar 2021)

・What do we know about each vaccine's efficacy?

Both mRNA vaccines are remarkably effective. In large clinical trials (Efficacy and Safety of the mRNA-1273 SARS-CoV-2 Vaccine by L.R. Baden et al., and Safety and Efficacy of the BNT162b2 mRNA Covid-19 Vaccine by F.P. Polack et al.) that enrolled tens of thousands of people, the vaccines lowered the chance of developing Covid-19 by around 95% as compared with placebo injections. As summarized quite accurately in this XKCD cartoon, sometimes data are so strong we don't even have to do a statistical analysis -- that's what happened with both of these clinical trials. The results were that good.

Although we consider data from randomized, placebo-controlled trials to be the strongest form of clinical evidence, additional details make the results even more compelling. First, the vaccines prevented not only any disease due to SARS-CoV-2, but -- quite importantly -- severe disease. Prevention of severe disease could convert Covid-19 from the global threat it is now into more of a nuisance, like the common cold. Second, the studies enrolled participants who were quite representative of the U.S. population -- age, sex, race, and ethnicity all broadly included. Third, while both vaccines are given as two doses, some protection became apparent just 10 to 14 days after the first dose.

The efficacy noted after the first dose has raised questions about whether we should be vaccinating twice as many people with one dose rather than giving people the full two-dose schedule. However, the 95% vaccine efficacy results come after the second dose, which boosts the immune response and is likely to make it more durable. For now, in the United States, the Centers for Disease Control and Prevention (CDC) and Food and Drug Administration (FDA) recommend proceeding with the two-dose schedule whenever possible.

Overall, these impressive results put the two mRNA vaccines up there with our most effective vaccines to date -- more like measles than influenza vaccines, at least in the short term. The protection is far better than anyone anticipated, which is why many of us specialists in infectious diseases, virology, immunology, and public health become downright giddy when asked to discuss the vaccine's efficacy.

An important caveat to the favorable efficacy results in the clinical trials is that the performance of the vaccines in clinical practice -- the effectiveness -- may be different. Although the study population in both studies includes people at high risk for Covid-19 complications, participants had to be clinically stable and sufficiently healthy to come in for their study visits. We do not yet know how effective the vaccines will be in a sicker population, such as the frail older people of advanced age living in nursing homes, or the severely immunocompromised. Population-based studies that include hundreds of thousands of people ultimately will give us a better sense of these "real world" data. (Last reviewed/updated on 24 Feb 2021)

Covid-19 ワクチンリソースセンター(NEJM)①




ワクチンが注射されると、mRNAは注射部位付近のマクロファージに取り込まれ、スパイクタンパクを作るように指示する。スパイクタンパク質はマクロファージの表面に現れ、人間が感染を撃退する方法を模倣した免疫反応を誘発し、SARS-CoV-2の自然感染から身を守る。その後、体内の酵素がmRNAを分解し、処分する。生きたウイルスは関与せず、遺伝物質が細胞の核に入ることもない。 これらは、広く試験され、臨床現場で使用された最初のmRNAワクチンであるが、科学者たちは何年も前からmRNAワクチンの研究を行ってきた。あるパロディ記事では、この技術は「当たり前」だと言っているが、実際には、mRNAを脂質でコーティングして劣化を防ぐという画期的な洞察は非常に素晴らしいものである。(最終更新日:2021年2月24日)


どちらのmRNAワクチンも非常に有効である。数万人を対象とした大規模な臨床試験(Efficacy and Safety of the mRNA-1273 SARS-CoV-2 Vaccine. by L.R. Baden et al.およびSafety and Efficacy of the BNT162b2 mRNA Covid-19 Vaccine. by F.P. Polack et al.)において、ワクチンはプラセボ注射と比較して、Covid-19の発症確率を約95%低下させた。XKCDの漫画に非常に正確に要約されているように、統計的な分析をする必要がないほど強力なデータが得られることがあるが、この2つの臨床試験ではそれが実現した。この2つの臨床試験結果はそれほど良かった。






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