At present, a large-scale vaccination of COVID-19 is carrying out around the world, bringing hope for alleviating the epidemic situation of COVID-19’s. However, due to the menacing invasion of various SARS-CoV-2 variants the protective effectiveness of vaccine has also been challenged.
Recently, the research team from Tel Aviv University in Israel conducted a survey of Israeli vaccinated people to assess the protective effectiveness of the mRNA vaccine BNT162b2. The results of the study were published in Nature under the title Evidence for increased breakthrough rates of SARS-CoV-2 variants of concern in BNT162b2-mRNA-vaccinated individuals. The study suggests that in a specific time window, the protective effectiveness of mRNA vaccine BNT162b2 against two newly-discovered SARS-CoV-2 variants decreased. Therefore, more stringent tracking of virus variation should be carried out and vaccination should be increased to prevent the spread.
Studies showed that in clinical trials, BNT162b2 is 95% effective in preventing COVID-19’s symptomatic diseases, and has shown the same high protective effect in the real environment in Israel. However, with the continuous increase of SARS-CoV-2 variants, there are more and more evidences that these variants may weaken the protective effect of COVID-19 vaccine. Therefore, it is urgent to test whether they can break the immune defense effect of COVID-19 vaccine on human body.
In this study, the researchers investigated the symptomatic or asymptomatic people who had been vaccinated but were still infected with SARS-CoV-2 in Israel’s Clalit Health Service Center, and divided the subjects into three groups. The first group was those who tested positive for PCR between 14 days after the first administration and 6 days after the second administration. The second group was PCR-test positive within 7 days after the second vaccination, and the last group was the control group, using the same number of unvaccinated people who were positive for PCR in the same period as the other two groups. Finally, 813 nasopharyngeal swab samples were collected and sequenced, including 149 pairs of Group 2-control group, 247 pairs of Group 1-control group, and other unsuccessfully sequenced samples.
After all the samples were sequenced, only two varieties of SARS-CoV-2, B.1.1.7 and B.1.351, appeared in the samples, of which B.1.1.7 was the main virus variety in Israel, while B.1.351 accounted for only 1.6% of all samples. The researchers hypothesized that B.1.1.7 might have mild vaccine resistance, while B.1.351 had higher vaccine resistance. The results showed that the proportion of B.1.351 infection in Group 2 was significantly higher than that in the control group without vaccination. About half of the cases in Group 2 were PCR-test positive 7-13 days after the second administration. About half of the cases were PCR-test positive within 14 days or more after the second administration. In the Group 1, the infection rate of B.1.1.7 was significantly higher than that of the control group.
These results show that there will be vaccine breakthrough infections in two specific time windows, and the proportion of variants will increase meanwhile. Given these results, the researchers said that current studies may show that the mRNA vaccine BNT162b2 is less effective in preventing B.1.1.7 variants in the first few weeks after the first vaccination. In addition, since some countries have chosen to increase the interval between the first and second administrations of mRNA vaccine BNT162b2 from the recommended three weeks to a longer time, it should be more rigorous to assess whether this delay will affect the immune defense effectiveness of populations receiving only the first dose against the new variants. But at the same time, because of the complexity of the time difference between the emergence of SARS-CoV-2 variants in Israel and the small number of samples, the results of this study need to be viewed more rationally and objectively.
At present, there are two mRNA vaccines available around the world, of which BNT162b2, jointly developed by BioNTech and Pfizer, has been included in the World Health Organization’s emergency use list, and the other mRNA-1273, developed by Moderna, has more than 90% effectiveness in clinical trials.