Nine vaccines have been shown to be effective in protecting people from the symptoms of Covid-19, a disease that can result from infection with the SARS-CoV-2 virus. However, it is not yet known how well vaccines prevent people from getting an asymptomatic infection or transmitting the virus to others. Preliminary signs suggest that they are at least part of both.
Live updates: coronavirus pandemic
1. Why is this important?
While vaccination provides people with considerable insurance against Covid, which is sometimes fatal, there is so far no assurance that they will not be silently infected with and transmit SARS-CoV-2, potentially infecting people who are not immune. . Those who are infected but never develop symptoms are responsible for 24% of the transmission, according to an estimated study.
The more SARS-CoV-2 circulates, the more opportunities the virus has to move in ways that increase its ability to spread, make people sick and kill people, and avoid the immunity offered by existing vaccines or a past infection. Already, variants of the virus have appeared that seem to be more dangerous. Also, the use of vaccination to obtain so-called herd immunity, when an entire community is protected, although not everyone has been immunized, requires vaccines that prevent transmission.
2. Do vaccines stop infection and thus transmission?
Some do and some don’t. The gold standard in vaccinology is stopping infection as well as disease – providing so-called sterilizing immunity. But it is not always achieved. The measles vaccine, for example, offers it; the one for hepatitis B no.
Coronavirus pandemic: complete coverage
3. Do Covid vaccines need to prevent infection to stop transmission?
Not necessarily. To the extent that a vaccine prevents infection, it also prevents early transmission. But he can do the latter without doing the former. Because SARS-CoV-2 spreads through the respiratory particles in the throat and nose of an infected person, a vaccine that reduces the duration of infection, the amount of virus in the airway (viral load) or how often a infected person may cough decreases the likelihood that be passed on to others.
4. Why don’t we know if Covid vaccines prevent infection and transmission?
Vaccine testing studies were not designed to answer these questions first. Rather, they were designed to initially determine the more urgent issue of whether vaccines would prevent people from getting sick and overwhelming medical systems. To explore this question, researchers usually gave one group of volunteers the experimental vaccine and another group of equal size a placebo. After the total number of volunteers with Covid symptoms confirmed in the study reached a predetermined level, the investigators compared the number in each group to determine whether those who received the vaccine did significantly better than those who received placebo. For vaccinations that have worked, vaccine groups have had 50% to 95% fewer cases of the disease, which are called vaccine efficacy rates.
5. Why not check volunteers for asymptomatic infections?
This is a more complicated action, because the only way to find out about asymptomatic infections is to regularly test volunteers, who can be counted in the tens of thousands in an efficacy study. However, about two dozen studies involving vaccines that have been shown to prevent disease do just that.
6. What did they find?
The results so far are preliminary. The most extensive published data refer to the vaccine produced by AstraZeneca Plc. In a study in the UK, volunteers are screened for SARS-CoV-2 infections using self-administered weekly swabs for the nose and throat. According to the results of December 7, after a single dose, the group that received the vaccine had 67% fewer positive swabs than the placebo group, suggesting that the vaccine reduces infections as well as diseases. Earlier, Moderna Inc. reported similar results from people who received a single dose of the vaccine in November.
7. What other evidence do we have?
Data from Israel, which inoculated a higher percentage of its population than any other country, gives indications that the vaccine used there, from Pfizer Inc. and BioNTech SE, can reduce transmission even if it does not protect against infections. After more than 75% of people aged 60 or older received a dose of vaccine and only 25% of those aged 40 to 60 received it, researchers in the largest testing laboratory of the Israeli coronavirus analyzed their data. For those who tested positive for SARS-CoV-2, there was a noticeable difference between the two age groups in the average amount of virus found in the test swabs. The researchers estimated that vaccination reduces the viral load by 1.6 to 20 times in people who become infected despite the shot. Another study in Israel, following infected people after inoculation, found that the vaccine reduced its viral load fourfold. Also, a study of the Moderna Covid vaccine in monkeys suggested that it would reduce, if not completely prevent, the subsequent transmission of the virus.
8. When will we find out more?
As vaccination becomes more widespread, researchers should be able to discern the effect on infection and transmission patterns, although it may be difficult to distinguish the impact of inoculations from that of measures such as blocking and masking. Completion of vaccination tests to test for asymptomatic infections will provide additional information. Two trials are expected to be completed in April. However, one is from a vaccine from Sinovac Biotech Ltd. in China, which has a reported efficacy rate of up to 50% against symptomatic diseases. The other tests performed by the Russian Gamaleya Research Institute, whose effectiveness rate against symptoms was 92% in clinical trials, but it is a small study. September should bring the completion of significant studies of highly effective vaccines. The results for the photos that proved to be the most effective in preventing disease (95%), from Moderna and Pfizer-BioNTech, are not expected until October 2022 and January 2023, respectively.
Live updates: coronavirus pandemic
1. Why is this important?
While vaccination provides people with considerable insurance against Covid, which is sometimes fatal, there is so far no assurance that they will not be silently infected with and transmit SARS-CoV-2, potentially infecting people who are not immune. . Those who are infected but never develop symptoms are responsible for 24% of the transmission, according to an estimated study.
The more SARS-CoV-2 circulates, the more opportunities the virus has to move in ways that increase its ability to spread, make people sick and kill people, and avoid the immunity offered by existing vaccines or a past infection. Already, variants of the virus have appeared that seem to be more dangerous. Also, the use of vaccination to obtain so-called herd immunity, when an entire community is protected, although not everyone has been immunized, requires vaccines that prevent transmission.
2. Do vaccines stop infection and thus transmission?
Some do and some don’t. The gold standard in vaccinology is stopping infection as well as disease – providing so-called sterilizing immunity. But it is not always achieved. The measles vaccine, for example, offers it; the one for hepatitis B no.
Coronavirus pandemic: complete coverage
3. Do Covid vaccines need to prevent infection to stop transmission?
Not necessarily. To the extent that a vaccine prevents infection, it also prevents early transmission. But he can do the latter without doing the former. Because SARS-CoV-2 spreads through the respiratory particles in the throat and nose of an infected person, a vaccine that reduces the duration of infection, the amount of virus in the airway (viral load) or how often a infected person may cough decreases the likelihood that be passed on to others.
4. Why don’t we know if Covid vaccines prevent infection and transmission?
Vaccine testing studies were not designed to answer these questions first. Rather, they were designed to initially determine the more urgent issue of whether vaccines would prevent people from getting sick and overwhelming medical systems. To explore this question, researchers usually gave one group of volunteers the experimental vaccine and another group of equal size a placebo. After the total number of volunteers with Covid symptoms confirmed in the study reached a predetermined level, the investigators compared the number in each group to determine whether those who received the vaccine did significantly better than those who received placebo. For vaccinations that have worked, vaccine groups have had 50% to 95% fewer cases of the disease, which are called vaccine efficacy rates.
5. Why not check volunteers for asymptomatic infections?
This is a more complicated action, because the only way to find out about asymptomatic infections is to regularly test volunteers, who can be counted in the tens of thousands in an efficacy study. However, about two dozen studies involving vaccines that have been shown to prevent disease do just that.
6. What did they find?
The results so far are preliminary. The most extensive published data refer to the vaccine produced by AstraZeneca Plc. In a study in the UK, volunteers are screened for SARS-CoV-2 infections using self-administered weekly swabs for the nose and throat. According to the results of December 7, after a single dose, the group that received the vaccine had 67% fewer positive swabs than the placebo group, suggesting that the vaccine reduces infections as well as diseases. Earlier, Moderna Inc. reported similar results from people who received a single dose of the vaccine in November.
7. What other evidence do we have?
Data from Israel, which inoculated a higher percentage of its population than any other country, gives indications that the vaccine used there, from Pfizer Inc. and BioNTech SE, can reduce transmission even if it does not protect against infections. After more than 75% of people aged 60 or older received a dose of vaccine and only 25% of those aged 40 to 60 received it, researchers in the largest testing laboratory of the Israeli coronavirus analyzed their data. For those who tested positive for SARS-CoV-2, there was a noticeable difference between the two age groups in the average amount of virus found in the test swabs. The researchers estimated that vaccination reduces the viral load by 1.6 to 20 times in people who become infected despite the shot. Another study in Israel, following infected people after inoculation, found that the vaccine reduced its viral load fourfold. Also, a study of the Moderna Covid vaccine in monkeys suggested that it would reduce, if not completely prevent, the subsequent transmission of the virus.
8. When will we find out more?
As vaccination becomes more widespread, researchers should be able to discern the effect on infection and transmission patterns, although it may be difficult to distinguish the impact of inoculations from that of measures such as blocking and masking. Completion of vaccination tests to test for asymptomatic infections will provide additional information. Two trials are expected to be completed in April. However, one is from a vaccine from Sinovac Biotech Ltd. in China, which has a reported efficacy rate of up to 50% against symptomatic diseases. The other tests performed by the Russian Gamaleya Research Institute, whose effectiveness rate against symptoms was 92% in clinical trials, but it is a small study. September should bring the completion of significant studies of highly effective vaccines. The results for the photos that proved to be the most effective in preventing disease (95%), from Moderna and Pfizer-BioNTech, are not expected until October 2022 and January 2023, respectively.