九强新闻

Science View: Evaluate The Effect Of Vaccination

Published:2021-02-01

Source:[英文]九强生物

Vaccine is the most important weapon for us to deal with COVID-19 now. After the new crown vaccine is injected, the neutralization antibody level can be detected by competition method, and the effect of vaccine can be expressed to a certain extent. It is still to be determined how long and how high titer neutralization antibody can produce protective effect. However, whether it is effective or not, no matter how long neutralization antibody can be maintained, the aim of the vaccine is to reduce the probability of infection. In order to "prevent from being affected", it is necessary to strengthen the epidemic prevention measures such as wearing masks, washing hands frequently and keeping social distance.

For the evaluation of vaccine effect, the most direct method at present is to expose the vaccinated people and the placebo people (whether they have been vaccinated or not, only the experimental designer knows, but the operators and volunteers do not know) to the same environment, and then compare the infection rate of the two groups. If the infection rate of the vaccine group is much lower than that of the placebo group, and the statistical analysis results are different, then the vaccine has protective effect. The phase 3 clinical trials of Pfizer and Sinopharm are similar to this scheme, and they all show very obvious protective effect, far higher than the 50% protection rate initially set by the World Health Organization.

Besides the most direct method mentioned above, is there any other way to measure or characterize the effect of vaccine? Of course, there are, but other methods simulate the process of real virus infecting human body to a certain extent. Since it is simulation, there must be information distortion.



1. Neutralization Antibody
This method is to simulate the process of virus infection by cell culture in vitro. If neutralizing antibodies are produced after vaccination, the process of virus infecting cells is blocked. Because of the existence of live virus, this method must be carried out in the Biosafety Level 3 laboratory. The whole experiment process is also time-consuming and labor-consuming, which generally takes 5-7 days to get the results. At present, this method is usually used as the gold standard for the detection of neutralizing antibodies. Vaccine manufacturers also mainly use this method in the vaccine development stage.

Note that this is the gold standard for the detection of neutralizing antibodies, not the gold standard for the detection of vaccine efficacy. Because the vaccine also involves the effect of cellular immunity, and this method can only detect humoral immunity, that is, the effect of producing antibodies (including neutralizing antibodies). In addition, due to the existence of new coronavirus mutants, different mutants may have different experimental results (that is, the vaccine may not be effective for all mutants).

2.Pseudovirus Experiment
As the name suggests, pseudovirus is used here, that is to clone the specific sequence of new coronavirus (RBD, S protein, etc.) into other viruses with low pathogenicity or no pathogenicity, and then use the packaged pseudovirus to attack cells. The advantage of this method is that it does not need to use a three-level laboratory, and can use fluorescence or enzyme for quantitative analysis.

3.Antibody Test
This is a field that IVD manufacturers are striving to explore. There are various methodologies and different names. The detection platform includes rapid detection card, biochemistry and chemiluminescence, etc. The common problems are as follows:

Total antibody
After vaccination or natural infection with NCV, all antibodies against NCV produced by the body include both neutralizing and non neutralizing antibodies; It contains not only IgG, but also IgM and IgA; It contains not only antibodies against S protein (or RBD), but also antibodies against N protein or other proteins. But at present, there are few kits that can detect all the above antibodies. Most detection kits can only detect antibodies against S protein or N protein. Therefore, antibodies against non-s protein or non-n protein will be missed.

neutralizing antibody
That is to detect the antibody with neutralizing activity to the new coronavirus. Neutralizing antibody is a functional concept, which emphasizes the function of this kind of antibody, namely neutralizing activity. The gold standard, of course, is the neutralizing antibody test of the new coronavirus mentioned in the first article. However, some neutralizing antibody detection methods have been developed on the platform of rapid detection, biochemistry and luminescence. It mainly includes:

1) Antibodies against the RBD region are regarded as neutralizing antibodies. When the new coronavirus infects human cells, the RBD domain of S protein of the virus binds to ACE2 receptor of human cells. Therefore, some manufacturers think that the antibody that can bind to RBD region is neutralizing antibody. However, strictly speaking, although RBD is the most critical region to mediate virus infection, not all antibodies against RBD are necessarily neutralizing antibodies. In addition, not all neutralizing antibodies are targeted at the RBD region. Therefore, the reliability of this method is questionable;

2) ACE2 can bind to RBD, and neutralizing antibody can also bind to RBD. Therefore, neutralizing antibody can also be detected by competitive method. This method introduces competition, and simulates the process of antibody blocking the virus (here is the RBD domain on the virus) into the cell (here is the ACE2 receptor on human cells) to a certain extent, so it can ensure that the detected antibody must have neutralizing activity, but it will still miss the neutralizing antibody against the non RBD region.

Either way, the results of neutralizing antibody can be quantitative or qualitative. At present, it is not clear which titer of neutralizing antibody can give sufficient protection to human body, so that people will not be infected with new coronavirus.

IgM or (and) IgG
At present, there are also kits for detecting new crown IgG or IgM on the market. These two kits can monitor the immune status of the body after vaccination. IgM generally reaches the peak in 7-14 days after vaccination, and IgG generally reaches the peak in about one month. However, there is no direct relationship between these two antibodies and neutralizing antibodies (it is generally believed that neutralizing antibodies are mainly IgG, but neutralizing antibodies only account for a small part of IgG, and the detection results of IgG can not reflect the level of neutralizing antibodies), and the detection results of IgM and IgG can not be used to evaluate whether the vaccine is effective or not.



The main methods to detect the effect of new coronavirus vaccine in vitro are the above. After vaccination, if you want to test whether the vaccine is effective, of course, it is the new coronavirus neutralization antibody test as the gold standard. However, this method has low detection flux and is difficult to detect on a large scale. Considering the accessibility and cost, the results of neutralizing antibody detection by competitive method can indicate whether the vaccine can achieve the expected effect to a certain extent. However, it should also be noted that even the neutralizing antibody test of new coronavirus, as the gold standard, ignores half of human immunity cellular immunity. The main reason is that the effect of cellular immunity is relatively more difficult to evaluate and quantify.

Conclusion:
Vaccine is the most important weapon for us to deal with COVID-19 now. After the injection of new crown vaccine, the level of neutralizing antibody can be detected by competitive method to characterize whether the vaccine can produce effect to a certain extent. How long and how high titer of neutralizing antibody can produce protective effect remains to be determined. However, no matter whether it is effective or not, no matter how long the neutralizing antibody can last, the purpose of the vaccine is to reduce the risk of infection. In order to "prevent the disease before it happens", it is necessary to strengthen the anti epidemic measures such as wearing masks, washing hands frequently and keeping social distance.