As we all know, vaccination is the most effective and economical measure to prevent infectious diseases.
Since the pandemic, numerous research institutions around the world have developed hundreds of new crown vaccines with various technical pathways, and more than 13.3 billion doses have been administered worldwide (the latest WHO data), and the global population has approached 2 doses per capita. Why has such widespread vaccination not only failed to eliminate the pandemic, but has helped control it much less than expected?
This did not surprise scientists.
As early as the early days of the pandemic, some knowledgeable scientists predicted that the new crown epidemic would not be eliminated and that the pandemic would transition into a local epidemic.
There are two main reasons for this:
First, because the new coronavirus is the most likely RNA virus to mutate, and new variants that continue to emerge will likely escape immunity induced by natural infection or vaccination;
Second, based on the understanding of other human coronaviruses, whether it is natural infection or immunity against the new crown induced by vaccination, it is difficult to maintain for a long time, and it will inevitably decay or even disappear over time, eventually making the once immunized become susceptible again; The constant replenishment of susceptible people through this cycle allows the virus to spread pronouncedly cyclically, known as endemic endemism.
Moreover, even if the virus does not mutate significantly, without considering the immune escape of the new variant, just because the "own power" of immunity weakening can make the epidemic endemic.
The reality of the development of the pandemic confirms this prediction of scientists.
Just yesterday, 5 May 2023, the WHO declared that the pandemic no longer constitutes a public health crisis of global concern, the pandemic has ended; But it also acknowledged that the virus will continue to spread widely.
In a recent study published in JAMA Network Open, researchers conducted a systematic review and meta-analysis using secondary data from 40 published studies screened from nearly 1,000 retrieved articles, showing that the efficacy of vaccine-induced immunity in preventing Omicron infection decays rapidly, and by 6 months; Relatively speaking, the decline in efficacy in preventing infection with the Delta strain is much slower.
Specifically, the researchers analyzed nearly 1,000 articles on the immune efficacy of the new crown vaccine that could be retrieved as of October 19, 2022, and selected 40 eligible studies on the immune efficacy of vaccines against the Omicron and Delta strains, and conducted a secondary meta-analysis of the original data.
The temporal stratification of vaccine efficacy was assessed at intervals of 1, 3, 6 and 9 months after the last dose of vaccination.
The results of the study showed:
Immune efficacy against symptomatic disease
Prevention of Omicron infection after completing any primary vaccination cycle (1 or 2 doses, depending on the vaccine) showed a significant decrease in immunity to symptomatic disease over time, from 52.8% at 1 month to 14.3% at 6 months, and further to only 8.9% at 9 months.
The efficacy of several common vaccines also differed slightly, with the efficacy of Moderna mRNA-1273 vaccine, Pfizer BNT162b2 vaccine, Esconley adenovirus vector vaccine ChAdOx1 nCoV-19 and Sinovac CoronaVac inactivated vaccination at 1 month 61.9%, 59.3%, 45.9% and 32.4%, respectively. At 9 months for the first three vaccinations and 6 months for Sinovac CoronaVac vaccination, the immune efficacy dropped below 5%.
In contrast, the reduction in immunity efficacy of several vaccines against symptomatic disease following Delta infection was much lower, at 79.6%, 58.5%, and 49.7% overall at 1, 6, and 9 months after primary vaccination.
Further evaluation revealed that the vaccine-induced half-life for preventing symptomatic disease of the Delta strain was 316 days, compared to 87 days for Omicron.
It is no wonder that the rate of reinfection in the population before the emergence of Omicron was very low, and after Omicron became commonplace.
Immune efficacy against symptomatic disease after Omicron infection can return to comparable levels shortly after primary vaccination with a booster dose, but subsequent immune decay similar to that after primary vaccination occurs.
Overall, the immunization efficacy was 60.4% at 1 month of booster dose, and decreased to only 13.3% at 9 months; The booster has an immune efficacy half-life of 111 days.
Immunological efficacy in preventing laboratory-confirmed infections
Immunization efficacy against Omicron infection after completing any primary vaccination cycle decreased from 44.4% at 1 month to 20.7% at 6 months and 13.4% at 9 months.
Similarly, the efficacy of the Delta strain against laboratory-confirmed infection was higher than that of Omicron, which was 80.5% at 1 month and 54.6% at 6 months after vaccination. It remained at 45.9% at nine months.
The half-life of immunity against laboratory-confirmed Delta strains is as high as 540 days, compared to only 143 days for Omicron.
Immunization efficacy for laboratory-confirmed Omicron infection with booster doses decreased to 36.0% at 6 months and 28.9% at 9 months.
Age groups with prophylactic laboratory confirmation of immunity to infection are stratified by the age group
Laboratory-confirmed immunity against Omicron infection did not differ significantly between younger and older groups, with 39.2% versus 38.7% at 1 month, 13.6% vs. 13.1% at 6 months, and 7.4% vs. 6.4% at 9 months compared with the under-18 age group, significantly lower than the efficacy against Delta.
In short, studies have shown that whether it is a primary vaccination or a booster dose, and no matter what type of vaccine, the immune efficacy of the new crown vaccine to prevent Omicron infection will rapidly decay over time, and by 6 months, the protective power will almost deteriorate and lose its protective power.
The WHO declared the pandemic over on May 5, and the pandemic will become a long-term health problem. Even without considering the problem of immune escape caused by new coronavirus mutations, the rapid decline of immune efficacy over time alone dooms vaccination to protect people from repeated infections, which means that the population immune barrier is more dependent on people's repeated infections.
In this way, for healthy people, the cost-benefit ratio of continuing vaccination in the future is not high enough, and the necessity of vaccination will naturally not be high. However, for vulnerable people with higher rates of severe disease and mortality after infection, regular vaccination like the flu vaccine is necessary.