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After recurrence data from 500,000 people in Israel who received the Pfizer vaccine, researchers suggest that a single dose provides adequate immunity after about 21 days, thus supporting your UK decision to delay the second dose to 12 weeks.
Pandemic of coronavirus disease 2019 (COVID-19) caused by the acute acute coronavirus 2 (SARS-CoV-2) respiratory syndrome has spread rapidly across the globe for over a year. Although countries have implemented a number of prevention strategies, things are still going up in many parts of the world. With the approval of many vaccines, however, it is hoped that the pandemic will be brought under gradual control.
To prevent the growing number of cases, in the UK, the Joint Committee on Vaccination and Vaccination recommended that a second dose of vaccine should be given 12 weeks after the first after a few days as in Phase III tests. The idea behind this was that giving the people at least twice a dose in a short time would help to reduce the number of cases and possibly reduce the severity of disease.
There is evidence to suggest that an increase in the gap between the Oxford AstraZeneca vaccine would not adversely affect the protection offered, but data are not yet available for the Pfizer vaccine.
However, a recent report looked at 500,000 people in Israel who received the Pfizer vaccine from the day after the first dose to day 24. They compared the number of infections in these people between days 13 and 24 with the those between days 1 and 12 and confirmed that the efficacy of the vaccine was only 51%. However, they also found that diseases began to decrease immediately after day 18. However, the study did not determine efficacy in this last period. This would have given a better estimate of the effectiveness of the vaccine if the second dose was given after 12 weeks.
A single dose of vaccine can still provide immunity
Therefore, a team of researchers from the University of East Anglia, UK, has updated this data to find out how effective a single dose of the Pfizer vaccine would be in a real situation. A paper was published in the medRxiv * a preprint server reports their results.
Using data from the previous study, the team analyzed vaccine efficacy between days 13 and 24 and modeled daily efficacy using Monte Carlo simulations.
The results of the model showed a total of 3,077 cases over the 24 days, close to the 3,098 cases reported. They found that the vaccine had no effect until day 14, but after that, the efficacy reached 91% to day 21 and then decreased.
Thus, the effect of vaccination in this population set gradually increased from day 14, peaking at around 90% at day 21. This indicates that the vaccine is very effective. after one dose, but only after about three weeks.
However, there was an increase in the number of cases in the first week after vaccination. This may be because people were less careful after receiving the dose. If so, the true efficacy of the vaccine may be higher even after the first dose.
Support for delaying the second dose
With regard to the analysis presented in the previous study, the authors note that, since they included data from days when the vaccine was ineffective, the analysis does not provide information on efficacy if the second dose has been delayed. In addition, their analysis may include mild cases as well, but most Phase III vaccine tests show that they are effective in reducing malignancy. disease rather than mild disease. Therefore, real efficacy in preventing serious disease and death may be better than the level calculated here.
Although the duration of protection after the first three weeks is not known, studies show antibody levels to the natural infectious decay of SARS-CoV-2 over time but remain stable over six months. Therefore, the protection is unlikely to decline until the second increase is increased at 12 weeks.
This analysis therefore reveals strong protection with the Pfizer vaccine starting 21 days after the first dose and supports UK policy of delaying the second dose of all vaccines.
* Important message
medRxiv publish preliminary scientific reports that are not peer-reviewed and, therefore, should not be seen as final, guiding health-related clinical practice / behavior, or be treated as information established.