COVID-19 Archive

Covid-19 Vaccine Resource Center(NEJM 2021.4.2)②

Frequently Asked Questions

・How long will the vaccines work? Are booster doses required?

Since the vaccines have been tested only since the summer of 2020, we do not have information about the durability of protection. Data from the phase 1 trial of the Moderna vaccine suggested that neutralizing antibodies persisted for nearly 4 months, with titers declining slightly over time. Given the absence of information on how long the vaccines will be protective, there is currently no specific recommendation for booster doses. However, both companies are developing vaccines that could be administered as boosters, and that also have coverage for emerging variants of SARS-CoV-2 less susceptible to vaccine inhibition. (Last reviewed/updated on 24 Feb 2021)

・Will the vaccines work against the emerging strains of SARS-CoV-2?

Currently there is limited information on how effective the mRNA vaccines will be against emerging strains of SARS-CoV-2. Both clinical trials preceded the identification of the major variants present now in multiple countries around the world. Studies suggest that the vaccines might be more protective against some of the variants than others, so no broad generalization about vaccine activity against variants is possible. An important limitation of these studies (which used samples from immunized or recovered people in the lab to assess neutralization) is that protection afforded by vaccination is more complex than simply measuring antibody responses. Molecular sequencing of the viruses from incident cases of Covid-19 that occur after vaccination will be important to help understand this important issue. Such cases should be reported to state health departments; the CDC plans to collect information about them, including sequencing if possible. In addition, information about these cases should be reported to the Vaccine Adverse Event Reporting System (VAERS).

In one study. opens in new tab, the Moderna vaccine's level of neutralizing antibody titers was six times lower with the B.1.351 variant than with earlier variants. Though the company says the titers still should be protective, they are developing a booster vaccine specifically to address this difference. Nonetheless, from a practical perspective, the discovery of these variants does not change the basic recommendations for vaccination. Specifically, right now it is not recommended that people wait for a new or changed vaccine in the hope that it will be more effective against emerging SARS-CoV-2 variants, though both Pfizer and Moderna are developing modifications to their existing vaccines designed specifically for broader activity against emerging strains. (Last reviewed/updated on 5 Mar 2021)

・Do the vaccines prevent transmission of the virus to others?

Many commentaries on the results of the original vaccine clinical trials cite a lack of information on asymptomatic infection as a limitation in our knowledge about the vaccines' effectiveness, specifically related to the spread of the disease. Indeed, this is a theoretical concern, since up to 40% of people who get infected with SARS-CoV-2 have no symptoms but may still transmit the virus to others.

However, emerging evidence now strongly suggests that mRNA vaccine recipients are less likely to transmit infection to others. In a large observational study conducted in Israel, those who had been vaccinated had a 90% reduction in the risk of asymptomatic infection compared with those not vaccinated. Furthermore, among those who do get infection after vaccination, it appears that viral loads are lower than in infected people who have not been immunized. opens in new tab. Lower viral loads most likely lead to reduced risk of transmission. These data serve as a reminder that many vaccines in wide use today powerfully protect against both disease and transmission -- so much so that infection control is one of the main motivators behind some vaccine policies.

Of note, while the vaccines do reduce the risk of transmission, we cannot say they eliminate it -- the protective effect will never be 100%. As a result, until case numbers are down and a higher proportion of the population has received their vaccines, we should continue to emphasize to our patients that vaccination does not allow us to stop other important measures to prevent the spread of Covid-19. Mask wearing in public, social distancing, and avoiding crowded indoor settings remain important strategies for now. (Last reviewed/updated on 24 Feb 2021)

Covid-19 ワクチンリソースセンター よくある質問(NEJM)②




現在のところ、新興株のSARS-CoV-2に対してmRNAワクチンがどの程度有効であるかについては、限られた情報しかない。どちらの臨床試験も、現在世界の複数の国で発生している主要な変異種が確認される前に行われた。研究によると、ワクチンはある種の変異種に対して他の変異種よりも防御力が高い可能性があるため、変異種に対するワクチンの活性を広く一般化することはできない。これらの研究(中和を評価するために、実験室で免疫を獲得した人や回復した人のサンプルを使用した)の重要な限界は、ワクチン接種による防御は、単に抗体反応を測定するよりも複雑であるということである。ワクチン接種後に発生したCovid-19の症例から得られたウイルスの分子配列を調べることは、この重要な問題を理解する上で重要である。このような症例は、州の保健局に報告されるべきである。CDCは、可能であれば配列決定も含めて、これらの症例に関する情報を収集する予定である。さらに、これらの症例に関する情報は、Vaccine Adverse Event Reporting System(VAERS)に報告されるべきである。







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