Israel started offering third doses to over-60s the Pfizer/BioNTech vaccination in the summer. It was the first country in the world to offer booster shots to those who had been vaccinated for at least five months. After a Leumit Health Services study, which was an Israeli healthcare provider, revealed that people over 60 who were vaccinated for more than five years had three times the chance of contracting the disease than those who were vaccinated less than five months ago, Naftali Bennett, the prime minister, made the announcement. Israel started offering a third dose for everyone 12 years old and over who had been waiting this long. It is up to other countries whether they will follow Israel's example.
In the New England Journal of Medicine (NEJM), the first data evaluating early effects of the third dose program were published last week. It was found that over 1.1 million people aged 60 and older received their third dose of Delta virus vaccine, which is extremely contagious in Israel and around the world. They were 11.3 times less likely than before to contract the disease.
Third doses of the vaccine are very effective in preventing Delta infection, provided that they are administered to those who are willing to get vaccinated. Third doses reduce the risk of infection by reducing the person's susceptibility. This creates a barrier against the spread and onward transmission of the virus. This is crucial because increasing numbers of people get infected even though they have been vaccinated. However, the risk of serious illness, spread, and infection are greater for those who have not been vaccinated. They also have the same peak levels of virus as those who are not vaccinated, which contributes to the rapid spread of the virus.
The third dose stimulates the production of stronger and more broad-based neutralizing antibodies than those produced by the second dose. Booster jabs can be used as an immunological refresher and an immunological upgrade. This immune buffer is superior to the Sars-CoV-2 Delta variant and can be used to reduce the risk of infection. This buffer is expected to decrease the need to boost in the future as higher levels neutralising antibodies are predicted be to confer longer-lasting immunity.
While other countries have closely analyzed the Israeli data, they have been reluctant to accept universal third doses of vaccines for younger people due to two reasons. Second, the current vaccine programs outside Israel still protect against severe disease, hospitalisation, and death. Although this is an acceptable standard for evaluating vaccine safety, it is not the only one. Despite widespread vaccinations, the devastating impact of Delta variant infections on hospitalisations in many US locations demonstrates the limitations of this benchmark.
A reasonable alternative standard to assess vaccine impact is the prevention even of mild infections, in order to minimize transmission within communities. There are still many people who have not been vaccinated and are not adequately protected against infection or transmission. Large populations (e.g. young children) are not allowed to be vaccinated. This has allowed the spread of Delta infections.
The NEJM paper highlights the importance of reducing the number people infected by the virus among those who have been vaccinated at least three times. This dramatically reduces the risk of spreading the virus to others. This concept is being tested in Israel, with encouraging results. These programs must be implemented alongside efforts to immunise the most vulnerable people. Even with creative strategies and financial incentives, it has been hard to persuade unvaccinated people. There is still a large portion of the population that would be eager to receive third doses as soon they are available. Third-dose programs would be a direct benefit to this motivated group as well as their communities. Meanwhile, programmes to promote immunizations for unvaccinated persons continue.
The second concern is that programs like Israels can perpetuate inequalities. There is no doubt that more vaccines are needed in more areas. Third-dose programmes should be considered in countries that have been exposed to the virus and are currently experiencing Delta outbreaks. Although the initial clinical trials showed that two-dose vaccines were effective in providing short-term protection, newer data suggest that a primary series of immunizations should be followed by an additional dose several months later. This schedule is also used for the hepatitis B vaccine and other viral vaccines.
However, this does not mean that all other countries should be neglected. The potential need for three vaccine doses in order to reduce the global threat of Covid-19 should be a strong signal to invest immediately into sustainable immunisation programs worldwide. The infrastructure needed to support sustainable programs would have the side effect of increasing access to critical vaccines that are not yet available everywhere. For instance, only 75% of African infants receive the three doses of the Hepatitis B vaccine. It is not uncommon to make such large-scale, transformative infrastructure investments in public health. UNAids estimates more than 70% of HIV-infected people have access to sustainable antiretroviral medication.
Countries with a vaccine supply are facing a difficult winter. Data from other countries with different demographics and Covid-19 epidemics can be viewed suspiciously. It is difficult to compare the Israeli experience with countries that use different vaccine types and different timings of vaccination. They also have different socioeconomic conditions and Covid-19 burdens. However, the biology of SarsCoV-2 immunity is the same regardless of where you are located in Tel Aviv or Toronto. The Israeli pioneering work in making third doses mandatory provides a model for other countries. It also ensures that the global standard for vaccination is followed by everyone no matter where they are located.
