Why are counties having an extensive outbreak of COVID-19?
There are a number of reasons why countries have extensive outbreaks of COVID-19: presence of specific variants, proportion of non-immune population, degree of implementation of mitigation strategies among others. While the Israelis have an excellent healthcare system and have been successful at getting a sizable part of their population vaccinated, they still have a large % of the population that remains unvaccinated (37%), they had a period of time of exceptionally loose to no mitigation strategies, had opened borders just prior to their spike and have part of their population who are relatively non-compliant with mitigation strategies (and also have lower vaccine uptake frequently). Additionally, they have a higher population density, particularly in the cities. Taken together, these have contributed to the high rates of infection currently seen. Interestingly, for nearly every wave of the pandemic, Israel has had higher infection rates that many other countries (including the US). While the focus has been on antibody titers and the potential need for booster shots, there are other contributors to their current and prior outbreaks.
Vaccines Immune Responses.
Vaccines produce 2 types of immune responses – humoral (antibody) responses and cellular responses. The antibodies can protect against infection if the antibody is able to bind the virus well (a good match for the circulating strain or variant) and is at sufficient levels in the blood. If the virus changes or the levels drop too much, an infection (often called a breakthrough infection) can occur. We see this with the influenza vaccine when the virus changes and isn’t well matched in a particular year to the components of the vaccine.
The cellular response to vaccine generally is much longer lived and is generally retained even if the virus changes over time. The cellular responses clear the virus and are responsible for the virus clearing more quickly, patients having milder symptoms and reducing the frequency of severe infections, those that require hospitalization or cause death.
Based on current US data, the vaccines are still working exceptionally well. The vaccines reduce the risk of infection 5x compared to an unvaccinated person and result in > 10x lower rates of hospitalization and death in vaccinated patients compared to unvaccinated patients (https://www.cdc.gov/mmwr/volumes/70/wr/mm7037e1.htm?s_cid=mm7037e1_w).
Lastly, its important to remember vaccine are only a part of the measures we can use to control COVID-19 and keep individuals safe. When vaccine is added to mask use, social distancing and hand hygiene, risk declines even further. When cases are high, as they are now, it is critical that we use the full range of mitigation strategies to keep everyone safe.