Nine vaccines have proven effective in protecting people from developing the symptoms of Covid-19, the disease that can result from infection with the SARS-CoV-2 virus. However, it is not yet known to what extent inoculations prevent people from contracting 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?
Although vaccination offers people considerable insurance against falling ill with Covid, which is sometimes fatal, so far there is no guarantee that they will not be silently infected with SARS-CoV-2 and spread it, potentially making people who are not immune sick. . Those who are infected but never develop symptoms are responsible for 24% of transmission, a study estimated.
The more SARS-CoV-2 circulates, the more opportunities the virus has to mutate to increase its ability to spread, get sick and kill people and escape the immunity provided by existing vaccines or a previous infection. Variants of the virus have appeared that appear to be more dangerous. In addition, the use of vaccination to achieve so-called herd immunity, when an entire community is protected, although not all have been immunized, requires vaccines that prevent transmission.
2. Do vaccines not prevent infection and therefore transmission?
Some do and some don’t. The gold standard in vaccinology is to stop infection as well as disease – providing so-called sterilizing immunity. But it is not always achieved. The measles vaccine, for example, provides; hepatitis B does not.
Coronavirus pandemic: complete coverage
3. Should Covid vaccines prevent infection to stop transmission?
Not necessarily. To the extent that a vaccine prevents infection, it also prevents direct transmission. But you can do the last one without doing the first. Because SARS-CoV-2 spreads through 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 respiratory tract (the viral load) or the frequency with which a infected person coughing can decrease the likelihood of being passed on to other people.
4. Why don’t we know if Covid vaccines prevent infection and transmission?
Trials that test vaccines have not been set up to answer these questions first. Instead, they were designed to initially determine the most urgent question of whether vaccines would prevent people from getting sick and overburdening medical systems. To explore this issue, the researchers typically gave a group of volunteers the experimental vaccine and another group of equal size a placebo. After the total number of volunteers with confirmed Covid symptoms in the study reached a predefined level, the researchers compared the number in each group to determine whether those who received the vaccine did significantly better than those who received the placebo. For the inoculations that worked, vaccine groups had 50% to 95% fewer cases of disease, numbers known as vaccine efficacy rates.
5. Why not check for asymptomatic infections in volunteers as well?
This is a more complicated task, as the only way to find out about asymptomatic infections is to regularly test the volunteers, who can reach tens of thousands in an effectiveness test. Still, about two dozen studies involving vaccines proven to prevent disease are doing just that.
6. What did they find?
The results so far are preliminary. The most extensive data released concerns the vaccine made by AstraZeneca Plc. In a UK study, volunteers are screened for SARS-CoV-2 infections using weekly self-administered nose and throat swabs. 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 and also illnesses. Moderna Inc. previously reported similar results from people who received a single dose of their vaccine in November.
7. What other evidence do we have?
Data from Israel, which inoculated a larger percentage of its population than any other country, provides clues that the vaccine in use there, from Pfizer Inc. and BioNTech SE, may reduce transmission even if it does not protect against infection. After more than 75% of people aged 60 and over received a dose of the vaccine and only 25% of people aged 40 to 60, researchers at Israel’s largest coronavirus testing laboratory 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 smears. The researchers estimated that vaccination reduces the viral load 1.6 to 20 times in individuals who are infected despite the injection. Another study in Israel, tracking people who became infected after inoculation, found that the vaccine reduced their viral load four times. In addition, a study of the Modern Covid vaccine in monkeys has suggested that it will reduce, if not completely prevent, the transmission of the virus.
8. When will we know 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 blocks and mask orders. Completion of vaccine testing for asymptomatic infections will provide additional information. Two tests are expected to end 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 the injection from the Russian Research Institute Gamaleya, whose rate of effectiveness against symptoms was 92% in clinical trials, but is a small study. September is expected to bring about the conclusion of considerable testing of highly effective vaccines. The results of vaccines that have been shown to be most effective in disease prevention (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?
Although vaccination offers people considerable insurance against falling ill with Covid, which is sometimes fatal, so far there is no guarantee that they will not be silently infected with SARS-CoV-2 and spread it, potentially making people who are not immune sick. . Those who are infected but never develop symptoms are responsible for 24% of transmission, a study estimated.
The more SARS-CoV-2 circulates, the more opportunities the virus has to mutate to increase its ability to spread, get sick and kill people and escape the immunity provided by existing vaccines or a previous infection. Variants of the virus have appeared that appear to be more dangerous. In addition, the use of vaccination to achieve so-called herd immunity, when an entire community is protected, although not all have been immunized, requires vaccines that prevent transmission.
2. Do vaccines not prevent infection and therefore transmission?
Some do and some don’t. The gold standard in vaccinology is to stop infection as well as disease – providing so-called sterilizing immunity. But it is not always achieved. The measles vaccine, for example, provides; hepatitis B does not.
Coronavirus pandemic: complete coverage
3. Should Covid vaccines prevent infection to stop transmission?
Not necessarily. To the extent that a vaccine prevents infection, it also prevents direct transmission. But you can do the last one without doing the first. Because SARS-CoV-2 spreads through 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 respiratory tract (the viral load) or the frequency with which a infected person coughing can decrease the likelihood of being passed on to other people.
4. Why don’t we know if Covid vaccines prevent infection and transmission?
Trials that test vaccines have not been set up to answer these questions first. Instead, they were designed to initially determine the most urgent question of whether vaccines would prevent people from getting sick and overburdening medical systems. To explore this issue, the researchers typically gave a group of volunteers the experimental vaccine and another group of equal size a placebo. After the total number of volunteers with confirmed Covid symptoms in the study reached a predefined level, the researchers compared the number in each group to determine whether those who received the vaccine did significantly better than those who received the placebo. For the inoculations that worked, vaccine groups had 50% to 95% fewer cases of disease, numbers known as vaccine efficacy rates.
5. Why not check for asymptomatic infections in volunteers as well?
This is a more complicated task, as the only way to find out about asymptomatic infections is to regularly test the volunteers, who can reach tens of thousands in an effectiveness test. Still, about two dozen studies involving vaccines proven to prevent disease are doing just that.
6. What did they find?
The results so far are preliminary. The most extensive data released concerns the vaccine made by AstraZeneca Plc. In a UK study, volunteers are screened for SARS-CoV-2 infections using weekly self-administered nose and throat swabs. 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 and also illnesses. Moderna Inc. previously reported similar results from people who received a single dose of their vaccine in November.
7. What other evidence do we have?
Data from Israel, which inoculated a larger percentage of its population than any other country, provides clues that the vaccine in use there, from Pfizer Inc. and BioNTech SE, may reduce transmission even if it does not protect against infection. After more than 75% of people aged 60 and over received a dose of the vaccine and only 25% of people aged 40 to 60, researchers at Israel’s largest coronavirus testing laboratory 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 smears. The researchers estimated that vaccination reduces the viral load 1.6 to 20 times in individuals who are infected despite the injection. Another study in Israel, tracking people who became infected after inoculation, found that the vaccine reduced their viral load four times. In addition, a study of the Modern Covid vaccine in monkeys has suggested that it will reduce, if not completely prevent, the transmission of the virus.
8. When will we know 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 blocks and mask orders. Completion of vaccine testing for asymptomatic infections will provide additional information. Two tests are expected to end 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 the injection from the Russian Research Institute Gamaleya, whose rate of effectiveness against symptoms was 92% in clinical trials, but is a small study. September is expected to bring about the conclusion of considerable testing of highly effective vaccines. The results of vaccines that have been shown to be most effective in disease prevention (95%), from Moderna and Pfizer-BioNTech, are not expected until October 2022 and January 2023, respectively.